Underground coal gasification

Gordon R Couch CCC/151 July 2009 Copyright © IEA Clean Coal Centre ISBN 978-92-9029-471-9

Abstract

The report describes progress with the development of underground coal gasification (UCG), which has the potential to increase the world’s resource of useable coal. The technologies involving the drilling of injection and production wells into the coal seam are described, together with the methods for linking the wells. With advances in methods for directional drilling in-seam, new techniques for UCG have proved to be possible. The test and trial work carried out in the former USSR, in China, Europe and the USA up to 2000 is described, along with current efforts to commercialise the technology. With the power of modern computers, the modelling of various aspects of the process has become possible, and current work should facilitate the validation of some of these models. Geological and hydrogeological issues are discussed, as the single most important decision that will determine the technical and economic performance of UCG is site selection. The report covers environmental issues, including carbon management, and discusses the options for the use of the syngas formed. The recent pilot-scale tests in Australia, Canada, China and South Africa are reviewed, together with other current proposals for further trials in a wide range of countries including India, Russia, the UK and the USA. Acronyms and abbreviations

ASPEN Advanced System for Process Engineering ASU air separation unit BHEL Bharat Heavy Electricals Ltd (India) bit bituminous BP British Petroleum CAER Centre of Applied Energy Research (University of Kentucky, USA) CBM coal bed methane CCS carbon capture and storage CEPL Carbon Energy Pty Ltd COS carbonyl sulphide CRIP controlled retraction injection point CSIRO Commonwealth Scientific and Industrial Research Organisation (Australia) CTL coal to liquids CUMTB China University of Mining and Technology, Beijing CV calorific value (heating value) DOE Department of Energy (USA) DTI Department of Trade and Industry (UK) EIA environmental impact assessment EOR enhanced oil recovery EPA Environmental Protection Agency ␧UCG Ergo Exergy proprietary technology ␧UCG™ FCL forward combustion linking FSU former Soviet Union GAIL Gas Authority of India HUGE Hydrogen oriented underground coal gasification for Europe HV high volatile IGCC integrated gasification combined cycle IIT Indian Institute of Technology (Mumbai) IP intellectual property IPCC International Panel on Climate Change IPPC Integrated Pollution Prevention and Control Regulations LHV lower heating value LLL Lawrence Livermore Laboratory (the predecessor of the LLNL) LLNL Lawrence Livermore National Laboratory LTLSTS long tunnel large section two stage (or LLTS) LV low volatile LVW linked vertical well MOU memorandum of understanding MV medium volatile MWD measurement while drilling n/a not available NCC National Coal Council (USA) NEDO New Energy and Industrial Technology Development Organisation (Japan) NTPC National Thermal Power Corporation (in India) OCGT open cycle gas turbine ONGC Oil and Natural Gas Corporation (in India) PDU process development unit PEDL petroleum exploration and development licence PPC Pollution Prevention and Control Regulations R&D research and development RCL reverse combustion linking SDB steeply dipping bed SNG substitute natural gas STL syngas to liquids subbit subbituminous (coal) TDR time domain reflectometer TEB triethylborane UCG underground coal gasification UGCp Underground Coal Gasification Partnership (UK) USBM United States Bureau of Mines USSR Union of Soviet Socialist Republics (up to 1991) VWs vertical wells WGS water gas shift (reaction) Widco Washington Irrigation and Development Company 2D/3D two/three dimensional

2 IEA Clean Coal Centre Units bbl/d barrels per day (of liquids products) ºC degrees Centigrade d day ha hectare kg kilogramme km kilometre m metre mm millimetre MJ/kg megajoules per cetre cubed MJ/m3 megajoules per metre cubed MPa mega pascal (pressure) MWe megawatts (electrical) Mya million years ago PJ petajoule t tonne y year

Conversion 1 Btu/ft3= 0.037 MJ/m3

Underground coal gasification 3 4 IEA Clean Coal Centre Contents

Acronyms and abbreviations...... 2

Contents...... 5

List of figures ...... 7

List of tables ...... 9

1 Introduction ...... 11

2 UCG potential ...... 13 2.1 Coal reserves and resources...... 13 2.2 Coal properties...... 14 2.3 Coal seam properties affecting UCG...... 16 2.3.1 Coal rank ...... 16 2.3.2 Seam depth and inclination ...... 17 2.3.3 Seam thickness ...... 18 2.3.4 Coal permeability ...... 18 2.3.5 Seam structure ...... 18 2.3.6 Associated geological and hydrogeological conditions ...... 19 2.3.7 Surface requirements ...... 19 2.4 Coalbed methane ...... 21

3 UCG technologies ...... 22 3.1 UCG chemistry ...... 24 3.2 UCG methods ...... 27 3.2.1 Using LVWs with hydrofracturing ...... 28 3.2.2 Using LVWs with in-seam boreholes...... 30 3.2.3 Using the CRIP configuration ...... 30 3.2.4 In steeply dipping seams ...... 30 3.2.5 Using man-made excavations...... 31 3.2.6 Advanced technologies...... 31 3.3 Establishing underground linkages ...... 35 3.3.1 Hydrofracturing and reverse combustion ...... 35 3.3.2 Directional drilling ...... 37 3.4 Igniting the gasifier ...... 41 3.5 Monitoring ...... 42 3.6 Well design and operation ...... 43 3.7 Operating with a CRIP ...... 43 3.8 Shutting down a UCG reactor ...... 44 3.9 Summary and discussion ...... 45

4 The main trials ...... 48 4.1 In the USSR ...... 49 4.2 In Europe ...... 53 4.3 In the USA ...... 57 4.4 In China ...... 62 4.5 The outcome from the trials ...... 64

5 Prospective developments ...... 66 5.1 Australia...... 67 5.1.1 Linc Energy ...... 67 5.1.2 Carbon Energy ...... 69 5.1.3 Cougar Energy ...... 71 5.1.4 Altera Resources...... 72 5.1.5 Liberty Resources...... 72 5.1.6 Metro Coal ...... 72 5.2 Brazil ...... 72 5.3 Canada ...... 72 5.4 China ...... 73 5.5 EU HUGE project ...... 74 5.6 India ...... 74 5.7 Ireland ...... 76 5.8 Japan ...... 76

Underground coal gasification 5 5.9 Kazakhstan...... 76 5.10 New Zealand ...... 76 5.11 Poland ...... 77 5.12 Russia ...... 77 5.13 Slovakia ...... 79 5.14 Slovenia ...... 79 5.15 South Africa ...... 80 5.15.1 Eskom’s development at Majuba ...... 80 5.15.2 Sasol pilot trial at Secunda...... 82 5.16 UK ...... 84 5.17 USA ...... 86 5.17.1 Wyoming...... 86 5.17.2 Indiana ...... 86 5.18 Vietnam ...... 87 5.19 Discussion and summary ...... 87 5.19.1 Factors affecting the control of the reactor ...... 88 5.19.2 The use of laboratory simulations ...... 88 5.19.3 Resource utilisation efficiency ...... 88

6 Geological and environmental impacts...... 90 6.1 Exploration requirements...... 91 6.2 Site selection constraints ...... 91 6.2.1 Geological and hydrological assessments ...... 94 6.3 Environmental impacts ...... 96 6.4 Monitoring possibilities ...... 97 6.4.1 Monitoring wells ...... 97 6.4.2 Managing ground deformation...... 97 6.5 Regulatory frameworks ...... 98

7 Modelling ...... 101

8 Syngas use...... 105

9 Carbon management ...... 108

10 Key requirements during the next five years ...... 111 10.1 Undertaking demonstration-scale projects ...... 111 10.1.1 UCG economics ...... 112 10.2 Establishing a science and technology roadmap ...... 114 10.3 Regulatory harmonisation ...... 115 10.4 Improving the public perception of UCG ...... 115 10.5 Meeting the skills shortage ...... 116

11 Conclusions ...... 117

12 References ...... 121

6 IEA Clean Coal Centre List of figures

Figure 1 Pie charts showing the world’s energy reserves and resources (GasTech, 2007a) ...... 14

Figure 2 Energy recovery comparison (Mallett, 2008) ...... 14

Figure 3 The impacts of UCG on the strata above the seam (Mallett, 2008) ...... 19

Figure 4 Schematic of the processes involved in UCG (Ökten and Didari, 1994; Chaiken and Martin, 1992; Beath and others, 2004)...... 24

Figure 5 The development of an UCG cavity/reactor (Perkins, 2005) ...... 25

Figure 6 The generic methods for UCG using drilled wells, as used in the US DOE trials (modified from Beath and Su, 2003; Davis, 2009)...... 29

Figure 7 Methods involving man-made excavations and conventional underground mining (Ökten and Didari, 1994; Beath and Su, 2003)...... 32

Figure 8 Texyn ‘Santa Barbara’ mining system (Tillman, 2008)...... 33

Figure 9 The super daisy shaft concept (Palarski, 2007)...... 34

Figure 10 The sequence of events in a UCG process using reverse combustion linking (Krantz and Gunn, 1982)...... 36

Figure 11 Schematic views of reverse and forward combustion linking (Blinderman and others, 2008b) ...... 37

Figure 12 Directional drilling, the challenges underground with alternative trajectories (Jackson, 2003; DTI, 2005) ...... 38

Figure 13 Downhole drilling assemblies (DTI, 2005) ...... 41

Figure 14 The progressive formation of new cavities as the CRIP is moved away from the production well (modified from Beath, 2004) ...... 45

Figure 15 Coal seam thickness and depth for the various field trials of UCG (Perkins, 2005; Beath and Davis, 2006) ...... 49

Figure 16 The linkage between holes at Podmoskovnaya (Gregg and others, 1976) . 52

Figure 17 The basis of the linear CRIP method. A schematic of an in-seam injection well and of a production well (Sury and others, 2004a) ...... 55

Figure 18 The Spanish linear CRIP test, and the way the cavities develop (Beath and Davis, 2006) ...... 56

Figure 19 Schematic view of the large block experimental configuration (Burton and others, 2006) ...... 60

Figure 20 Long tunnel large section in-seam gasification layout (Liang and Shimada, 2008) ...... 62

Figure 21 Map showing the location of UCG activities, past and present (Friedmann, 2008) ...... 66

Figure 22 The Bloodwood Creek layout with parallel-holes CRIP for the 100-day trial (Mark and Mallett, 2008)...... 70

Figure 23 Schematics of the new Russian technology for UCG (Zorya and others, 2009) ...... 78

Figure 24 Diagram of the Secunda UCG process showing the well matrix together with an elevation (Brand, 2008) ...... 83

Underground coal gasification 7 Figure 25 Map of UK prospect areas for UCG (DTI, 2004) ...... 85

Figure 26 Goafing behaviour: a) for a cavity larger than 100 m; b) for a cavity small enough not to break the dolerite sill on the surface (Brand, 2008). . 95

Figure 27 An integrated UCG simulation (Kolar, 2008) ...... 102

Figure 28 UCG syngas composition from various trials (Mark, 2008)...... 106

Figure 29 Tomorrow’s syngas to products business (Puri, 2006) ...... 107

Figure 30 Plans for UCG expansion to commercial scale using parallel CRIP (Mallett, 2007) ...... 113

8 IEA Clean Coal Centre List of tables

Table 1 Methane content in coals with increasing depth (Sloss 2005) ...... 20

Table 2 Summary of past experience with UCG in the USSR (Beath and others, 2004) ...... 50

Table 3 Summary of experience with UCG in Europe (Beath and others, 2004; Burton and others, 2006) ...... 53

Table 4 Outline details of the principal trials in the USA (Davis, 2009)...... 58

Table 5 Rawlins US DOE test results (Singleton and Pilcher, 2007) ...... 60

Table 6 Summary of experience with UCG in China (Beath and others, 2004; Feng Chen, 2008)...... 63

Table 7 The consortium partners for the HUGE project (Palarski, 2007) ...... 74

Table 8 Comparison of the resource utilisation efficiency of conventional mining and use with UCG (modified from Beath, 2006) ...... 89

Table 9 UCG site selection criteria ...... 93

Table 10 Goaf heights (Brand, 2008) ...... 95

Table 11 Typical UCG models which have been developed (modified from Kolar, 2008) ...... 103

Underground coal gasification 9 10 IEA Clean Coal Centre 1 Introduction

The concept of underground coal gasification (UCG) is simple. It involves reacting (burning) coal in situ/in-seam, using a mixture of air/oxygen, possibly with some steam, to produce a syngas. The steam may come from water which leaks into the underground cavity, from water already in the coal seam or from steam deliberately injected. Some coal combustion takes place generating enough heat to support the process reactions. Then gasification takes place at the elevated temperatures with a stoichiometric shortage of oxygen involving the partial oxidation of coal, so the principal gases formed are hydrogen and carbon monoxide. However, there are many other products, including carbon dioxide; hydrocarbons such as methane; tars; and compounds such as hydrogen sulphide and carbonyl sulphide (COS) arising from impurities in the coal. The product mix can vary widely depending on a number of factors. If the oxidant is air, there will be significant amounts of nitrogen present. The syngas produced is cleaned, and can be used to produce electric power or as a chemicals/liquid fuels feedstock. If air is used as the oxidant, the syngas has a heating value which is about one-eighth that of natural gas while if oxygen injection is used then it is about one quarter to one third.

UCG offers the potential for using the energy stored in coal in an economic and environmentally sensitive way, particularly from deposits which are unmineable by conventional methods. If UCG were to be successfully developed and widely deployed, then the world’s coal reserves might be revised upwards by a substantial amount. This is discussed in Chapter 2. Site selection of the places where UCG could be carried out is critical to any development since the geology must be appropriate.

The main method of achieving UCG involves a minimum of two boreholes (or wells) drilled into the coal seam some distance apart, and connected by a link/channel through which gases can flow. These holes may be vertical, or they can be inclined boreholes, partly drilled through the coal seam. One of the holes, referred to as the injection borehole, is used to supply the gasifying agent (air, oxygen enriched air, or oxygen, possibly with added steam). The other is the production borehole (or well) through which the product gases are carried to the surface for treatment and use. With some production patterns the function of these wells is interchangeable, and from time to time, the supply/injection well becomes the production well, and vice versa. This may be to achieve the linkage between them, or to smooth out the pattern of gasification in the (constantly changing) underground gasification chamber. Commercial-scale operations using UCG would involve multiple boreholes/wells to produce sufficient quantities of syngas, based around the two wells concept described above.

In spite of the fact that the techniques have been tested and developed over a period of more than fifty years, the author found that the technology is not well explained or discussed in the literature. This is mainly because: G much of the older work took place in the USSR and consequently there are both reporting and translation limitations. In addition the perception of ‘commercial’ operations was completely different from that prevailing now and there were few sensitivities relating to environmental impacts. At best, some of the Soviet work could correctly be described as being on an industrial scale; G the largest consistent test programme was that undertaken by the US DOE between 1973 and 1989. Many of the original reports are no longer available. Most information is therefore from second and third hand publications written by authors who were not part of the original project teams, introducing inevitable distortions; G publications about the results from current pilot projects are sketchy, and are limited by the fact that developers regard some of the knowledge as proprietary. Most seem to be unwilling to share their knowledge and experience, and with a fledgling technology such as UCG which is poorly understood by both developers and regulators, this could seriously affect its application.

During the past twenty years there have been significant advances in the techniques used for directional drilling and in particular for in-seam drilling in coal. This has been associated with the drilling needed by the oil and gas industries, and with that used for recovering coal bed methane (CBM). The UCG methods and well linkage techniques, including a discussion of in-seam drilling are covered in Chapter 3. Chapter 4 contains an account of the main trials carried out in various parts of the world, including the UCG work undertaken in China in abandoned mines to recover some of the coal/energy left behind. This involves a somewhat different approach from the ‘two boreholes’ method, and one approach used in China is based on man-made tunnels which form the gasification chamber.

Chapter 5 describes the ongoing efforts to establish the conditions for commercial development. As the reactor conditions are quite variable, it would almost certainly be necessary to operate a number of underground gasification ‘reactors’ in parallel in order to supply a consistent feed of syngas to a commercial operation. Then the syngas products can be combined to ensure adequate uniformity in terms of both quantity and composition.

Because the reactions take place underground and out of sight, control of key process parameters, such

Underground coal gasification 11 as temperature, is difficult. The coal seam and surrounding rock form a huge heat sink with the reactions taking place largely in one part of the seam at a given time, spread along the whole of the link between the two wells.

Only a limited number of parameters can be either controlled or measured, and it can even be difficult to determine where the reaction is taking place and what temperatures are reached. As a result, modelling has a substantial part to play in studying what is happening and this is discussed in Chapter 6. Modelling is also used in overall project assessment work and in designing the necessary surface facilities. Chapters 8 and 9 look at syngas use and carbon management respectively.

In this report, the potential for UCG use is discussed, with an outline of the main technologies which can be applied, and a description of the outcome of test work. The penultimate chapter, before the conclusions, looks at the key requirements during the next five years for the successful deployment of UCG on a commercial scale. Small-scale in-seam trials are an essential preliminary step, following the necessary exploration to identify potentially suitable sites, but commercial-scale applications are considerably more challenging and there is, as yet, virtually no relevant experience to build on.

12 IEA Clean Coal Centre 2 UCG potential

UCG is being looked at particularly for utilising unmineable coal deposits and deeper seams which are not included in the proved reserves figures. The amount of work carried out in deep seams is very limited. It can potentially be used in steeply dipping seams, and in coal deposits where the ash content is so high that it precludes conventional extraction. Nobody is currently looking at UCG in preference to conventional mining where the coal can be extracted economically using well proven methods, but if the technology becomes established during the next ten years or so, that situation might change.

Early studies suggest that the use of UCG could potentially increase world’s coal reserves by as much as 600 Gt (World Energy Council, 2007), which represents a 70% increase. As discussed in this report, UCG is not easy to carry out without environmental impacts, and the inability to manage these acceptably would reduce the amount of coal which can be utilised by this method. However, even an increase of 60 Gt (based on a conservative assumption that just 10% of the potential can be realised) would provide a significant amount of additional energy.

In today’s world, carbon management and the control of CO2 emissions are likely to become subjects which may determine the future of individual UCG developments. Carbon management is discussed in Chapter 9.

2.1 Coal reserves and resources

There is an important distinction between the ‘reserves’ and the ‘resources’ of all the fossil fuels. For coal, the geological resource is the total endowment of coal in a particular area, and while there are several uncertainties, some geologists believe that the world total is reasonably well known and assessed.

The ‘proved reserves’ are defined as ‘the amount of the coal which would be economically recoverable using current technology’. Then in addition, there are ‘probable’ reserves and then ‘possible’ reserves. Some commentators use the terms proved, indicated and inferred reserves/resources; others describe the ‘coal in place’ together with estimated additional amounts. Added together, the three amounts (proved, probable/indicated and possible/inferred) are the total potential resource of a fossil fuel. The figures for economically recoverable reserves are open to adjustment, in that as the relative price level increases, more of the resource becomes economically recoverable and thus becomes a proved reserve. This adjustment is not, however, made on a regular or consistent basis. The reserves figures commonly quoted by key information providers such as BP (2007) and the World Energy Council (2007) remain much the same from year to year even though coal prices and therefore what can be economically mined, may change significantly. The world’s proved reserves, which are the amount of coal assessed as being economically recoverable using current conventional mining technology, were estimated to be just under 850 Gt at the end of 2005 (World Energy Council, 2007). The equivalent figure in the BP Statistical Review of World Energy (BP, 2007) was 900 Gt. The total resource which would include thin seams, deep seams and those which are steeply dipping, could be anywhere between five and ten times this amount.

Coal deposits located at or near the surface can be extracted by open pit methods at depths down to 100 or 200 m. Underground mining of the deeper seams is possible at depths down to a little over 1000 m, although it gets increasingly expensive to ventilate and cool the deeper mines. Extraction costs increase at greater depths, and are proportionately higher for mining thinner seams.

The accuracy of the reserves/resources figure for any country or coal basin depends on the amount of detailed exploration undertaken, and this is highly variable. For the reserves amount, much depends on people’s assessment of what is economic. It is complicated by the fact that in spite of efforts to standardise, different countries (and multi-national companies) use different methods and conventions. Some data are regarded as commercially sensitive and are therefore not published by the companies involved.

Similar considerations apply to the world’s reserves and resources of the other fossil fuels, oil and natural gas. The relation between the established reserves of the main fossil fuels and of the total resources, is illustrated in Figure 1 where the predominance of coal is absolutely clear.

In terms of energy content, the world’s coal resources are vast, and are almost certainly much greater than those of the other fossil fuels, oil and gas. However, only a fraction of the energy can be recovered by conventional mining, some is recoverable in the form of CBM extraction, and considerably more would be recoverable if UCG is developed into a commercial-scale process. The order of magnitude of the different approaches is illustrated in Figure 2 which shows the potential energy recovery in a particular location, from CBM, by using conventional highly mechanised mining (where this is possible) and from UCG. The amounts of energy recoverable in practice will depend on a variety of different

Underground coal gasification 13 a) Reserves (economically recoverable) factors, many of which are discussed in this report. If the coal can be extracted economically by conventional mining methods, this may well be the preferred option in a particular location.

~ 900 Gt The assessment in Figure 2 is based on a typical coal 19% of coal deposit in the Surat basin in Queensland, Australia. The average seam thickness there is 7 m. The deposit is in an area comprising some 12 km2 and lies almost horizontally. Not all deposits can be mined conventionally, and any comparison is ‘coal deposit specific’, nonetheless the 17% diagram illustrates the potential for energy recovery using UCG and provides a indication of the orders of magnitude 64% involved.

2.2 Coal properties

The main reason for including a discussion about coal b) Resources formation in this study is to highlight the differences between the coals and their geological setting in different 2.2% 2.3% countries and areas. The coal properties and the adsorbed ~ 18 Tt gases in its pore structure will directly affect UCG of coal behaviour. Because some 85% of the coal mined globally is used inside the country of origin, different classification systems have been developed in coal-producing countries. For example quite different systems are used in Australia, China, Germany, Russia, the UK and the USA (see Couch, 2006). Similarly, many coal experts have developed an in- depth knowledge and understanding of their own coals and of their geological settings, but have relatively limited knowledge of the coals which occur in other places. Where coal is mined, geoscience expertise (comprising geology, hydrogeology and rock mechanics) is focused on its impact on conventional mine design, construction and operation. The behaviour of an UCG reactor/cavity and the effects of UCG on rock behaviour and water movement will be quite different, but it should be noted that the same skill set is required, albeit with a broader and more closely 95.5% related perspective (Van der Riet, 2009).

Oil Natural gas Coal Coal formation Coal is a combustible sedimentary rock containing both organic and mineral matter. The organic matter is derived Figure 1 Pie charts showing the world’s energy from vegetable material accumulated under conditions reserves and resources (GasTech, which have prevented complete decay. Subsequent burial 2007a) has formed a complex mixture of chemical compounds containing carbon, hydrogen and oxygen together with 1400 coal smaller amounts of nitrogen, sulphur and trace elements. The mineral matter consists chiefly of clay minerals, hydrogen 1200 mineral forms of sulphur (mostly pyrite) and smaller CO amounts of other minerals. Moisture is also an important 1000 methane constituent.

800 Variations in the physical and chemical characteristics of coal result from differences in: 600 G the original plant material from which coal is derived; Energy, PJ Energy, G the amount of decay that occurred before eventual 400 burial; G the amount of contamination by inorganic material 200 during deposition; G the temperature and pressure conditions that existed 0 during its geological history. The primary control on UCG underground coal seam the variations in coal properties is the burial historyof mining gas the original peat, which results in differences of coal rank, controlled by differences in the geological Figure 2 Energy recovery comparison (Mallett, conditions of temperature and, to a lesser degree, 2008) pressure during coalification. Time is not necessarily a determining factor. Increasing rank results in

14 IEA Clean Coal Centre progressive and irreversible changes in the chemical and physical properties of the coal, in the generalised sequence of:

peat r lignite r subbituminous coal r bituminous coal r semi-anthracite r anthracite.

Differences in the kinds of plant material and its biochemical alteration before burial affect the coal properties. The degraded plant components of coal are known as macerals which are analgous to minerals in rocks. The macerals form associations called lithotypes. Differences in the range of impurities present determine the grade of the coal (Sherwood, 2009).

Coal deposits have been formed in almost every geological period since the Carboniferous, 350–270 Mya (million years ago), and some even started during the Devonian, up to 400 Mya. Coal rank is only partly dependent on its age. The highest/higher ranks of coal have undergone the most coalification. This is a progressive process (based on bacterial decay encouraged by the application of heat and pressure) that turned decayed plant material into the various ranks of coal. The first stage in the progression from peat to lignite mainly involves decay while the remaining stages are thermal. The major by-products from coalification are methane, carbon dioxide, and water. Hence the presence of CBM, and of liquid water both of which can be held in the pore structure.

The effect of coalification is to progressively increase the content of carbon. It is a dehydrogenation process with a reaction rate slower by many orders of magnitude than that of carbonisation. The degree of coalification increases progressively and can be defined by means of the measured C/H ratio and of the residual contents of oxygen, sulphur and nitrogen. Among the properties which change with rank and which will affect UCG are the moisture content (which is generally highest in low rank coals) and permeability. Broadly the low rank coals tend to be more permeable with a looser pore structure, and this will affect their behaviour significantly during in situ gasification. Low rank coals are also, generally, more reactive and will have more organically bound impurities.

The post-Carboniferous coals are found mainly in the southern hemisphere; in the western USA and in parts of Europe. The world’s major coalfields are described and discussed in an IEA Clean Coal Centre report by Walker (2000). If UCG is developed on a commercial scale it is likely to prove possible to extract substantial amounts of coal which are unmineable by conventional means, and that may include coal which lies more than 1000 m deep, and some which lies under the sea (on a continental shelf).

Coals of all ranks from lignite to anthracite can be gasified in surface gasifiers, although different conditions may be used and the range of syngas products can be markedly different. In addition, there are significant technical challenges in feeding coal (which is a solid) into a vessel at high pressure, and in subsequently depressurising and cleaning the products.

While the tests on UCG have included coals of different ranks, many have been of short duration and the overall results have been inconclusive. It appears that subbituminous and high volatile bituminous coals may be easier to gasify underground than the higher rank ones. It seems likely that this is associated with their inherent permeability and, because they tend to shrink when heated, the linkage between the injection and production well is more readily enhanced. The inherent moisture content of these coals is also high, so that the product syngas may have a higher water content, but less steam injection may be needed. It has been suggested that in lower rank coals some of the impurities might act as catalysts and improve the kinetics of the gasification (Burton and others, 2006). Development work relating to the possibilities of gasifying higher rank bituminous coals and also lower rank lignites is ongoing.

Variability The geological setting of different coal deposits is highly variable with seams at different depths, inclination, seam thickness, and involving different interactions with adjacent structures and formations. This includes the permeability and strength of rock formations in various layers both above and below the coal seams. It also includes the hydrogeology of the formations, as some water around a target seam is desirable, but the contamination of aquifers should be avoided. It is these geological factors that are likely to present the major challenges to UCG development and there are not yet enough validated geologic assessments to provide a secure basis for ensuring satisfactory conditions for undertaking UCG.

The coals themselves are also highly variable, and as a crude illustration, the coals currently used in different parts of the world, the range of properties/characteristics can be expressed as follows: G a LHV (lower heating value) from 5 MJ/kg to 30 MJ/kg; G ash content can go from 1% to 50% or even higher, although many standards do not define such material as coal; G similarly, moisture content can vary from 5% to 65%; G sulphur content can range from virtually nothing to as much as 10%; G the age of a given deposit can be from 350 My to as little as 2 My, and the temperatures and pressures experienced will depend on many factors, meaning that the degree of coalification is highly variable.

Underground coal gasification 15 The relevance of this to UCG is that trials and tests have so far only looked at a relatively narrow range of coals and geological settings, and the results obtained have been quite scattered, site-specific, and in many cases inconclusive in terms of whether large-scale development would be practical. This will be discussed further in Chapters 4 and 5.

Some people seem to have too readily generalised from the claim ‘this is what happened here in this particular context’ to ‘this is what happens in coal’ without recognising coal’s variability, and the massive differences in the geology and hydrology of different deposits.

Coal seam properties Coal properties are heavily dependent on the geological history of the seam in terms of the temperatures and pressures it has experienced and its age. If it came into contact with volcanic activity it may have seen very high temperatures and there may be intrusions of volcanic rock in parts of the seam. There may have been deposition into the layers from marine sources or from particles carried by the wind. Seams can have highly irregular interfaces with adjacent rock formations, and may contain large dirt bands of non-combustible material.

Coal is composed of distinct organic entities called macerals, and lesser amounts of inorganic minerals. Some impurities such as Ca, Na, N and S are attached to the organic coal structure of the coal. Others have been deposited as discrete mineral particles carried by rivers or from the sea or which may have been wind-blown. The macerals and minerals occur in distinct associations called lithotypes, and a coal seam can consist of a number of lithotype layers.

2.3 Coal seam properties affecting UCG

While the coal seam properties are important, as can be seen from the list below, it is the geological setting which determines the potential application of UCG, and this is discussed further in Section 2.3.6.

Key features which affect the use of UCG are: G the geological structures both above and below the coal seam. Particularly the properties of the roof materials above the seam, and of the hydrogeology of the area. If there is an impermeable seal between the coal seam and the surface, then the environmental implications are very different compared with those for a roof consisting of permeable shales or sandstones; G the amount of water available long-term to provide a seal around the reactor cavities to minimise the risk of gas escape, where this is necessary; G the deposit/seam depth, thickness and inclination; G seam continuity and its physical strength; G the nature of the coal (and in particular its rank and reactivity, together with its ash, moisture, sulphur and methane contents); G the permeability of the seams, based on the pore structure and the presence of cleats (or cracks). In addition, the presence of fracture planes or shear zones in or near the seam is of significance as these might provide leakage paths for the syngas formed; G an UCG activity expects some goafing (collapse) of the immediate overlying strata into the cavities created during gasification, and planning this forms part of the process. The extent and nature of subsidence through to the surface depends on the nature of the overlying strata and varies from site to site; G most of the ash in the coal remains underground and acts as a buffer to reduce subsidence developments on the surface. UCG requires a largely temporary infrastructure of wellheads and pipelines on the surface. A power generation unit and/or chemicals production facility to clean and use the syngas would occupy a relatively small area, but would be there for the life of the project, which might be 20 to 30 years. Carrying out UCG will be much easier under land which is undeveloped and where a small amount of subsidence is likely to be acceptable. It may also prove to be possible to recover energy from coal resources under the sea.

2.3.1 Coal rank Almost any coal apart from the swelling/caking coals can be gasified underground, but some will be easier to utilise than others. Coals which swell on heating and can be suitable for coke production are likely to be unsuitable for UCG as the linkages between the injection and production wells can be more readily blocked off. Coal rank will affect permeability and reactivity, and for some methods of UCG this will affect the operability of a reactor. It might be noted that anthracites are commonly associated with a relatively high geological risk (with high fault densities and the prevalence of igneous intrusions) while lignites and brown coals are often associated with poorly-cemented sands at relatively shallow depths and corresponding high hydrogeological risk (Rippon, 2009). Trials in higher rank coals including anthracites have been relatively few, as have trials in thick brown coal/lignite seams.

16 IEA Clean Coal Centre Considerably more work would be required to establish the conditions for an UCG operation in such coals.

2.3.2 Seam depth and inclination A feature affecting the use of UCG and its application is the deposit/seam depth. This affects: G the hydrostatic pressure in the seam and hence the operating range for the pressure in the underground reactor cavity; G the likelihood of causing significant subsidence at the surface. UCG carried out at greater depths will tend to cause less subsidence.

In many circumstances it is thought to be necessary to operate at below the hydrostatic pressure to ensure that water flows into the reactor chamber rather than out of it. This is to reduce the chances of water contamination, although at greater depths this may be less of an issue since many of the aquifers are already saline and not used as potable water. In shallow seams where the hydrostatic pressure is minimal, even transient increases in the reactor chamber pressure are likely to result in increased gas leakage. In deeper seams the hydrostatic pressure will be considerably higher and it should be easier to maintain relatively steady conditions. In some seams, particularly some deep seams in northern Europe, there may be an impermeable rock covering, possibly accompanied by a limited water supply, and here the rock layer may provide a shield which prevents gas losses. It is one of many aspects of UCG which are not explained clearly in the literature.

The hydrostatic pressure increases with depth at about 0.01 MPa/m for fresh water and 0.012 MPa/m for a saturated saline aquifer. This means that at 100 m depth the hydrostatic pressure is some 1 MPa, and at 1000 m depth it increases to a little over 10 MPa. These differences have a significant effect on the permissible operating conditions and thus on the composition and condition of the syngas formed.

In addition to changes in hydrostatic pressure with depth, the strata will increase in temperature, although this effect has much less impact. The temperature gradient varies in different places, but in Queensland, Australia, values of just over 2ºC/100 m are quoted, so that the strata at 1000 m deep will be some 20–25ºC hotter than that at 50 m deep.

Seam inclination (or dip) will have a considerable impact on UCG behaviour. It is discussed in more detail in Section 3.2.4. Positive results were reported from work in steeply dipping seams in the USSR (see Section 4.1) in terms of the increased heating value of the product syngas, but maintaining overall process control and preventing the escape of contaminants over a period, presents a significant challenge. Steeply dipping seams are often associated with disturbed geology which results in more challenging drilling conditions and in less predictable groundwater flows. As the hydrostatic pressure varies up and down the reactor it also presents greater process control problems than in a seam which is close to being horizontal.

In near horizontal seams where virtually all the current development work is taking place, it is important to start the reactor cavity at the lowest point in the seam to be extracted. The path taken by the cavity is then consistently updip, and as the reactions tend to propagate upwards rather than downwards this provides for a more natural progression.

The practicalities associated with an economic development mean that initially UCG is likely to proceed in seams that are broadly deep enough and with an appropriate water seal to eliminate the risk of gas leakage, but shallow enough to facilitate economic drilling. Most current developments are looking at seams deeper than 200 m which would minimise the risk of uncontrolled gas losses and of shallow aquifer contamination provided the reactor operating pressure can be appropriately controlled at a level below that of the prevailing hydrostatic pressure. Some commentators suggest that the minimum depth for effective UCG should be nearer 300 m, and in ground where there are no known seam discontinuities, but these judgements are of necessity site and coalfield specific. Others recommend that UCG should be used at depths greater than 500 m.

Walters (2009) comments that at shallower depths of <500 m, control of the gasification process presents a challenge. Gasification at depths >1 km can and will present engineering challenges, but the gasification should be more controllable.

The minimum depth appropriate for UCG will vary considerably both between and within coalfields, reflecting many technical factors, and also local regulatory regimes. Geological variables will include the permeability of the overburden and the presence of aquifers. Other technical variables will include design of the UCG operation itself, and any particular features requiring protection on the surface (Rippon, 2009). A key concern is the amount of imposed strain on the strata above resulting from the extraction of coal from an UCG reactor cavity, and possibly from the high temperatures involved which may affect the properties of the rock above.

Underground coal gasification 17 The need for a water seal may vary in different strata and seam depth. Most of the current group of pilot tests only cover the depth range from about 150 to 300 m, although one is at 1400 m.

In terms of the costs of UCG, the exploitation of deeper seams involves higher drilling costs, although any nearby aquifers are more likely to contain saline (non-potable) water thus reducing any risk of unacceptable contamination. Any aquifer contamination should be avoided since even if it flows slowly, its eventual path may well interact with others. Also, potable water is sometimes extracted from deep aquifers and, for example in Australia, it is taken from boreholes which can be up to 2 km deep (Beath, 2009). Another, unquantified, cost factor is that operations in shallower seams may require additional effort to keep the reaction zone hydraulically secure (to prevent contaminant escape) both during UCG operations and when a reactor is shut down (Rippon, 2009).

A major consideration when considering the desirability of working in deeper seams relates to the longer-term prospects for carbon capture and storage (CCS). At depths below about 800 m the hydrostatic/cavity operating pressure can be such that the CO2 formed can be subsequently captured as a supercritical fluid, thus facilitating its long-term storage in geological strata without additional compression costs. This is discussed further in Chapter 9.

Compared with conventional mining, UCG can probably be more readily used in coal seams that are faulted or steeply dipping. It might also be used where there are irregular intrusions into a seam which would make mining difficult. With UCG it should be possible to identify parts of the seam which can be economically exploited where conventional mining would be either uneconomic or even virtually impossible. However, there are limitations with the possible use of UCG in disturbed ground with increased risk of gas leakage and greater difficulty in controlling the movement of the reactor cavity. Activities in steeply dipping seams might be on a smaller scale compared with those in near horizontal seams.

2.3.3 Seam thickness Current developments seem to be mainly in seams around 5 to 10 m thick where there are substantial quantities of coal to be gasified but where cavity collapse would probably not result in unacceptable ground movement and subsidence.

If UCG is used in thick seams of >20 m it would seem that there is a greater risk of unexpected cavity collapse as it is not easy to forecast where the reactions will take place, and how they will move horizontally. A great deal more work is required to assess UCG applications in thick seams.

UCG has been proposed for use in thin seams less than 2 m thick, but while a syngas can be produced, there will be many questions relating to the potential economics of such an operation. The heat losses through the roof can be considerable, leading to low thermal efficiency and lower product gas quality. However, some groups are looking at the possibilities for exploiting seams which are only around 2 m thick, and these are described in Chapter 5 (see Sections 5.16 and 5.17.2).

2.3.4 Coal permeability The cleats/cracks in coal are associated with the geological stresses exerted on the seam when it has been subject to massive ground movement and may even have become folded over during the process. Stresses can result in the formation of tight closely-spaced fractures within the coal seam whose presence is of significance during UCG, and in relation to the release (and recovery) of CBM. In general, the higher rank coals and those in deeper seams have low/lower permeabilities. This will have an impact on the appropriate technology for making the necessary underground linkages to facilitate controlled UCG as well as on groundwater influx rates, and the distribution of water in the seam section being gasified.

2.3.5 Seam structure One of the characteristics of coal deposits is there is frequently a series of seams at different depths resulting from peat depositions which were maybe many thousands (tens and even hundreds of thousands) of years apart. These seams will be of varying thickness and quality, and in most sequences, only two or three seams might be mineable by conventional methods. If the top/shallowest seam is mined first, then lower seams are generally left undisturbed, for possible future extraction. Also of relevance is the fact that some coal seams contain significant amounts of methane gas, adsorbed in the pore structure. In some situations, the methane can be economically extracted for use as a fuel, and if UCG is considered in a particular coal deposit, the sequencing of the use of different technologies needs to be considered.

Some seams lie in horizontal or only gently inclined strata, while others have been folded over by geological action and lie at a steep angle. Coal-bearing successions can include many separate seams (coal horizons in geological terminology), with sometimes more than thirty horizons in the complete

18 IEA Clean Coal Centre sequence. Of these, it is common for only a few to be mineable by conventional methods. Seam thickness can vary from just a few centimetres up to amounts of more than 100 m. In the deeper bituminous coal deposits, the extracted seams commonly have a thickness of between 1 m and 4 m. There are substantial deposits at depths below 1000 m which cannot generally be extracted by conventional mining methods as the temperatures and pressures in the seam would be too high. If UCG could be established as a viable method for recovering the energy from such seams then the potential is enormous.

While the Soviets reported some success in gasifying steeply dipping seams (see Section 3.2.4), there are significant challenges in applying the methods used on a larger scale. Promgaz is still pursuing the possibilities in Russia (see Section 5.12).

2.3.6 Associated geological and hydrogeological conditions The various layers situated both above and below the coal will have a direct influence on whether UCG is possible in a particular location. This will include the roof materials above the seam, and other layers right up to the surface. The rock formation below the seam will be affected by the reactor temperatures as the heat may cause cracking. In relation to the layers underneath, it is well known from conventional longwall mining that strains can be introduced into the strata under the seam for a distance up to 50 m (Rippon, 2009).

The hydrogeology of the area involved is of crucial importance, and there should be sufficient water to provide a seal around the reactor which would prevent gas leakage where there is no impermeable rock formation above the seam to contain any leaking gas. The quality of the surrounding (and nearby) water is an issue, in that it is preferable that this is already of poor quality since this will reduce any sensitivity to potential contamination.

Choosing appropriate places for development involves not only understanding the geology and hydrogeology but also appreciating the potential effects of the presence of a moving reactor in the coal seam with reaction temperatures above 1000ºC. There will be a pattern of the collapse of the roof into the cavity, with resultant movement and cracking in the strata both above and below, depending on its properties and strength. The various effects are illustrated in Figure 3 including the effect on water flow, in an example of UCG in a relatively shallow seam. Modelling the changes can provide the basis for environmental management assessments.

subsidence and groundwater is modelled surface water table continuous deformation zone

water inflow

gasification chamber caved zone zone fractured gas pressure < water pressure coal seam

water flow into the cavity flushes chemicals in & they are removed with the syngas

Figure 3 The impacts of UCG on the strata above the seam (Mallett, 2008)

2.3.7 Surface requirements UCG activities can result in surface subsidence, and this effect may restrict the number of places where it will be practical to carry it out. Subsidence is generally a very gradual process, typically only involving a

Underground coal gasification 19 few centimetres in a year, and is dependent on the depth and thickness of the coal seam, on the amount of coal extracted, and on the nature of the overlying strata.

In conventional mining it is common practice to leave certain parts of the seam undisturbed so as to prevent damage to surface buildings and installations. A pillar of coal (sometimes quite a large pillar) will be left in place around the base of a mine shaft and other pillars will be left to prevent or minimise subsidence damage to surface buildings and to installations like railway lines. Pillars may also be left in order to prevent rivers and canals from subsiding. UCG can, in principle, be controlled and managed to achieve similar effects.

UCG will generally best be undertaken where the land (on the surface) is fairly open, undeveloped and of relatively low value. Using some UCG methods, the landscape will be punctured by a whole network of boreholes which are moved progressively across the surface as gasification of the underground seam proceeds. Other methods using inclined and in-seam boreholes should be less intrusive in terms of the pipework infrastructure, but subsidence effects will be much the same. All developments will require the provision of surface installations to supply the feed gases (including possibly oxygen and steam), to facilitate ignition of the underground seam, and to clean and use the syngas produced (either for power generation or chemicals/liquid fuels production). Developments will also require appropriate administration and laboratory buildings.

Table 1 Methane content in coals with increasing depth (Sloss 2005)

Depth interval, m Mean methane content, m3/t Range Number of assays

100 0.02 0.00-0.17 35

200 0.29 0.00-3.80 184

300 0.67 0.00-7.81 396

400 1.07 0.00-18.67 467

500 0.99 0.00-18.19 582

600 1.35 0.00-21.24 677

700 1.99 0.00-15.59 680

800 2.45 0.00-16.65 725

900 3.16 0.00-19.31 783

1000 3.73 0.00-18.13 894

1100 4.68 0.00-17.79 718

1200 5.19 0.00-17.82 664

1300 5.46 0.01-17.37 504

1400 5.17 0.01-13.67 413

1500 4.89 0.00-12.95 335

1600 5.57 0.30-15.33 162

1700 5.78 0.02-12.39 97

1800 6.60 0.07–16.05 85

1900 6.52 1.80-13.56 34

2000 7.09 2.68–13.34 24

2100 4.57 0.60-9.42 10

2200 3.97 3.04–5.36 5

2300 2.81 2.32-3.31 2

20 IEA Clean Coal Centre 2.4 Coalbed methane

Seams are highly variable in the amount of methane they may contain. During conventional mining, the methane released can be a safety hazard, and the control of mine ventilation using large amounts of air to prevent explosions, is a major consideration. Methane emissions also arise from old and abandoned mines. CBM recovery is discussed in another IEA Clean Coal Centre report Coalbed methane emissions – capture and utilisation (Sloss, 2005).

Some seams have enough methane to be economically recoverable independent of whether the coal itself will be mined conventionally, for example where the deposit is dipping or disturbed. CBM recovery has been carried out successfully on a considerable scale in both Australia and the USA, and is being actively considered or applied on a smaller scale in a number of other countries. The main method used is via vertical wells and the use of hydrofracturing to establish paths in the coal to facilitate methane release when the water is pumped out.

The success of a CBM project depends principally on the accessibility of the methane. The highest concentrations of methane are generally found in deeper coal seams, see Table 1. The release of methane gas from coal in order to allow its collection occurs only when the pressure is sufficiently reduced by removing ground water from porous, fractured coal formations. In an effort to increase the quantity of methane gas removed from coal seams, fluids are forced into the formation through a well at very high pressures to hydraulically fracture the coal seams. Sand particles in the hydraulic fluid prop up the widened and newly created fractures in the coal allowing more methane gas to escape after much of the hydraulic fluid and ground water have been pumped out of the wells. The in-seam drilling techniques established to facilitate CBM recovery can be useful for some UCG applications.

The possible sequence of energy recovery from coal seams has become the subject of dispute, linked to licencing arrangements, particularly in locations in Queensland, Australia (see Section 5.1.1). At this stage, CBM extraction in Australia and the USA is a considerably more mature technology than UCG, although much less energy is potentially recovered. The dispute which has arisen highlights the need for a consistent regulatory basis for the extraction of both energy and water from underground sources (see Section 6.5). It is likely to become increasingly important to avoid ‘sterilising’ a seam by extracting CBM in such a way that subsequent UCG becomes virtually impossible.

Underground coal gasification 21 3 UCG technologies

UCG requires a multi-disciplinary integration of knowledge from exploration, geology, hydrogeology, drilling, and of the chemistry and thermodynamics of gasification reactions in a cavity in a coal seam (DTI, 2004).

Historically and in most countries, there has commonly been relatively little contact and technical understanding between those who mine coal and others who use it. Even at an academic level, there are relatively few experts who can cut across the boundaries between the geologists and mining engineers responsible for coal extraction, and the chemical, process and combustion engineers largely responsible for its handling and use. As an example of the gap in technical understanding, the engineering community is generally not sufficiently familiar with geologic systems to know how to contain the syngas underground consistently. The current pilot UCG projects (see Chapter 5) are helping to bridge the gaps and cut across the boundaries, but the scale of this activity is still small and the results and experience gained have not, generally, been reported and discussed.

While UCG is simple in concept, it is complex in its application and execution. This is not, in the view of the author, reflected in much of the available literature.

As described in Chapter 2, the application of UCG requires an understanding of the geological setting of different coal deposits, their variability, and how they lie in different strata. Coal deposits are far more variable than those of the other fossil fuels, gas and oil, and this has a major impact on the ease of exploitation.

A number of techniques have been established to facilitate UCG, and four main methods are providing the basis for current industry developments. In addition there has been work in China to recover energy from abandoned mines and using man-made underground tunnels. There are a number of technical overviews of the status of UCG technologies, which include: G Review of the feasibility of underground coal gasification in the UK (DTI, 2004) prepared by the UK DTI; G Underground coal gasification: evaluating environmental barriers (Beath and others, 2004) written for the CSIRO, Australia; G Best practices in underground coal gasification. Draft (Burton and others, 2006) which is currently being updated by the LLNL, Livermore, CA, USA; G The urgency of sustainable coal (Nelson and others, 2008) published by the US National Coal Council (NCC).

In this chapter, the principles which lie behind the technology are discussed, while the experience gained from work in the USSR, USA, China and in Europe up to the 1990s is assessed in Chapter 4. Current developments in Australia, Canada, Russia, Europe, China and the USA, and proposals for the use of UCG in a variety of countries, are discussed in Chapter 5. Since there was some activity at the end of the 1990s, it is difficult to create a precise cut-off point, but generally work undertaken before 2000 is discussed in Chapter 4, while that since, much of which is ongoing and with a view to commercial development, is discussed in Chapter 5.

Controlling the reaction and producing a syngas with consistent quality and quantity with minimal environmental impact can be difficult to achieve.

There are key differences between surface and underground gasification: G on the surface the reactions are contained in a fixed vessel where the temperature and pressure can be measured and controlled with considerable precision, as can the feed of coal and oxidants. Under these conditions the quantity and composition of the products can be reasonably accurately predicted and controlled. There can, however, be some challenges in feeding coal as a solid into a pressurised vessel, and this may require the use of a lock hopper or feeding the coal as a paste. In addition, the behaviour of the ash can cause problems; whereas, G underground, the shape and location of the reaction zone will be continually and progressively changing and it is not possible to measure or control the operating conditions in the same way. The feed materials are all gases, as are the principal products, and the solid coal and char form the ‘boundaries’ of the underground reactor. During UCG there will be burn-out in the coal seam, with caving and thermal deformation in the surrounding rock formations. The reaction zone will be moving into different parts of the deposit, and this movement will not be precisely predictable and controllable. Some of the gaseous products may escape from the reactor zone into the strata, and the influx of water may or may not be controllable.

22 IEA Clean Coal Centre Historical overview The early history of UCG was slow and inauspicious. Sir William Siemens, a German scientist, is credited with the first suggestion to gasify coal underground in 1868. At about the same time, in Russia, Dmitriy Mendeleyev, suggested the idea of controlling and directing spontaneous underground coal fires, including the idea of drilling injection and production wells (Olness and Gregg, 1977). The first patent recorded for UCG was issued in 1909 in the UK to an American, A G Betts.

In about 1910, a special committee of Britain’s leading scientists was formed to investigate ‘national energy resources’. They made several proposals, involving: G the development of forests; G the use of solar energy; G using the earth’s internal heat, and/or the earth’s rotational energy; G the disintegration of elements; G the underground gasification of coal.

A member of this committee, the English chemist Sir William Ramsey, became very interested in underground gasification, and decided to pursue Betts’ method using a single borehole. In 1912, Ramsey lectured at the opening of an International Smoke Abatement Exhibition in London in which he explored and explained some of the potential virtues of in situ coal gasification such as: G clean air; G reduced transportation costs; G independence from the coal miners’ unions (England was in the middle of a coal miner’s strike at the time); G the use of gas turbines instead of steam turbines, which he believed to be twice as energy efficient.

Ramsey described his proposed gasification experiment in some detail. A bore hole would be ‘put down to the coal’ and air and steam passed through to make water gas where the coal was located, instead of raising it to the surface, to make the same gas. Ramsey’s ideas were widely circulated in the popular press, although he died before being able to pursue them and run practical test work. Lenin, living in exile in western Europe during this period, read reports of Ramsey’s speech and was intrigued by the humanitarian and social aspects of underground gasification. He was impressed by the potential for both inexpensive power and improved working conditions that might result from freeing the miners from the strenuous, backbreaking underground labour. On 4 May 1913, in Pravda, Lenin published a glowing account of Ramsey’s technique entitled One of the great triumphs of technology. The Soviet UCG programme was later championed by Joseph Stalin for the same reasons that had motivated Lenin.

In about 1928, Kirichenko started actively planning the first Soviet UCG experiments. He published an article in Ugol (Coal) in 1930, describing in technical detail his proposed method for in situ coal gasification. The work of implementing this method began at Lisichansk in 1932 (Olness and Gregg, 1977).

Details of the technical aspects of the Soviet programme are discussed in Chapter 4 and as most of the work was undertaken before the break-up of the Soviet Union, there are several references to the USSR. The programme was significantly downsized and lost its momentum in the 1960s, when large reserves of natural gas and oil were discovered in Russia. By 1996 (in the post Soviet era), when the last Russian UCG plant was shut down, the UCG plants in Russia and other countries of the FSU had only consumed some 15–17 Mt of coal. The plant at Angren, now in Uzbekistan, is still in operation. The total Soviet effort has far exceeded the combined efforts of those of other countries both in terms of numbers of tests and of the amount of coal gasified (Burton and others, 2006). Test work and trials in both Europe and in the USA have explored a wider range of conditions than were tried in the Soviet Union, and some sophisticated models have been developed.

Between the years 1944 to 1959, a shortage in energy resulted in new interest for UCG in Western European coal mining countries. Tests were carried out in Czechoslovakia, France (in Morocco), Italy, and Poland (Curl, 1979). The boreholes method was tested in the United Kingdom, on the sites of Newman Spinney and Bayton (1949-50). A few years later, a first attempt was made to develop a commercial pilot plant: the P5 Trial in Newman Spinney (1958-59). During the 1960s, all European work was stopped, principally due to an abundance of energy and to low oil prices.

European work restarted during the 1980s, with trials in Belgium and France, and culminated in the UCG test at El Tremedal in Spain which was undertaken jointly by Spain, the UK and Belgium, and supported by the European Commission. Two short tests there took place in 1997. There has been considerable interest in Europe in the gasification of deep seams with higher rank (bituminous) coals, compared with much other work which has been using coals of lower rank which are more naturally permeable.

In the USA, an UCG programme was initiated in 1972, which built upon Russian experience, as well as trying out new techniques. More than thirty field tests were carried out (Burton and others, 2006), and at the end of the programme in 1989, the technology was thought to be ready for commercial

Underground coal gasification 23 demonstration. Unfortunately, in terms of development, because the price of natural gas in the 1990s was low, no commercial demonstrations took place, and the skills developed have become diluted since most of the people involved in the US programme have either moved on to other jobs, or have retired. Almost all of the original reports written are out of print and unavailable. Most of accessible information is from second, third and even fourth hand publications, usually by authors who were not part of the original project teams. In many cases the information provided is distorted and possibly biased, which is a common problem with the recovery of technical information which has passed through several hands (Davis, 2009).

The largest on-going programme is being conducted by China, and includes at least sixteen trials, mainly in abandoned mines and/or developing their long tunnel two-stage technology based on man-made gasification chambers (discussed in Sections 4.4 and 5.4), although their most recent trial involves the two-borehole method.

There are active sites where pilot tests are currently being undertaken in Australia, Canada, China and South Africa, see Chapter 5. Feasibility studies and assessments are under way in a range of countries with several more planned pilots.

3.1 UCG chemistry

During gasification, the in-seam coal is heated by hot gases to a very high temperature and is consumed

gas exit air entry

temperature 200 - 550°C 550 - 900°C > 900°C

oxidation zone

reducing zone

drying and pyrolysis zone

pyrolysis reduction oxidation

coal CH + H O C + H O CO + H C + O CO 4 2 2 2 2 2

CO + CO CO + C 2 CO C + 1/ O CO 2 2 2 2

H + C CO + H O CO + H CO = 1/ O CO 2 2 2 2 2 2 2 hydrocarbons CO + 2H CH Coal + O CO + CO + H O 2 4 2 2 2

Figure 4 Schematic of the processes involved in UCG (Ökten and Didari, 1994; Chaiken and Martin, 1992; Beath and others, 2004)

24 IEA Clean Coal Centre Step 1: Drill wells and establish permeable link by oxidation reactions. Then in a region where the oxygen injection well production well content is depleted, the gasification reactions take place. A surface flame front is initiated within the passage linking the injection and production wells, and as the gases pass through the various reactions approach equlibrium conditions before they leave via the production well at level of water table temperatures which will probably be between 200ºC and 400ºC. Figure 4 is a schematic showing the various over-burden reactions taking place using the basic Russian coal seam methodology, with linked vertical wells (LVWs). There is a similar sequence of reactions when using any of the UCG configurations described later in the chapter. Figure 5 shows the changes in conditions through the gasification cavity right through to the final clean-up of under burden the remaining space when the useful coal has been reacted.

As the coal is heated (throughout the length of the combustion/gasification cavity and the linkage routes), the Step 2: Gasification of coal seam coal starts to lose the moisture held in the pore structure, injection well production well and then undergoes pyrolysis at temperatures above surface 400ºC, during which hydrogen-rich volatile matter is released, together with tars, phenols and hydrocarbon gases. Simultaneously, at higher temperatures, the char is gasified, releasing gases, tar vapours and solid residues. Details of the different processes of gasification, the over-burden reactions taking place and the chemistry involved can be found in the IEA Coal Research report Understanding coal gasification, Kristiansen (1996). The dominant coal seam gasification reactions are those of partial oxidation of the char which produces a syngas consisting mainly of hydrogen and carbon monoxide. Under some conditions the formation of methane is of considerable significance. under burden At the same time various impurities in the coal which may either be organically bound or in the form of discrete particles held in the matrix will also be reacting. Many coals have a significant pore structure with adsorbed gases Step 3: Cavity is flushed with steam and water and in particular methane, and this will be released and will contribute to the reactions taking place along the injection well production well reactor zones. As the product gas moves through the surface chamber and along the linkage channels to the production well and its temperature changes, there will be many gas phase reactions taking place.

over-burden The basic reactions can be generalised as: water floods cavity G C + O2 r CO2 (+ heat) G C + CO2 (+ heat) a 2CO coal seam G C + H2O (+heat) a H2 + CO G C + H2 a CH4 (+ heat)

In addition, during pyrolysis: under burden coal r char + tar + H2O + volatile gases

and the water gas shift (WGS) reaction changes the CO/H2 balance, depending on the conditions of temperature and Figure 5 The development of an UCG pressure, and on how much water vapour is present: cavity/reactor (Perkins, 2005)

CO + H2O a CO2 + H2

The heat needed to promote the formation of the H2+CO syngas comes principally from the oxidation of carbon to form CO2 (ie from combustion). At lower temperatures and pressures, carbon oxidation reactions dominate, leading to a high CO2 content in the product gases and a low heating value syngas. Such conditions are typical of shallower UCG operations. Pressure increases the proportion of the coal which is pyrolysed to form methane, thus increasing the heating value of the product gas (Creedy and others, 2004). Under underground conditions, once ignition has been achieved and a combustion zone established, the gas formed continues on its path to the production well and inevitably loses heat to its surroundings. This will be both in the form of sensible heat transferred into the coal seam and rock formation, and from the evaporation of any water present in the coal or which leaks into the chamber. The gas will also change in composition as the products of pyrolysis are added en route and its

Underground coal gasification 25 temperature falls, affecting the equlibrium of some of the reactions taking place.

Minerals which are naturally present in the coal may preferentially catalyse some of the reactions taking place. The WGS reaction (CO + H2O a CO2 + H2) can reduce the heating value of the product gas by replacing a CO molecule with a H2 one and a H2O one with CO2. The H2O can be readily condensed out when the gas is treated on the surface, whereas the CO2 is not so easily removed. Much depends on the intended use of the syngas, and whether it is to be used primarily for power production or whether it is for liquid fuels production where a higher proportion of H2 may be advantageous. For the downstream production of chemicals and liquid fuels, the gasifier needs to produce a syngas with a heating value broadly in the range 10.5–16 MJ/m3. The syngas could also be used as the fuel gas for an IGCC unit or for producing a substitute natural gas (SNG). On a smaller scale it can be used as a supplementary fuel in an existing coal-fired boiler.

The conditions are dependent on: G the rank of the coal involved and the seam thickness and depth; G the properties of the mineral matter and other impurities present; G the temperatures achieved underground, together with the reaction chamber pressure; G the size and shape of the connecting links, the shape of the developing cavity, and the distance to the production well; G the nature of the injection gas, and on whether it is air or oxygen-enriched air and on whether it carries any steam with it; G the UCG reaction zone is commonly surrounded by a water seal, and with a sufficient supply, water will flow into the reaction cavity where it will become steam. This applies generally to shallower UCG, while in deeper seams there may not be sufficient water, and the seal is provided by impermeable layers of rock above the seam.

Once the reaction has been established, the product gas composition can be modified to an extent by changing the feed rate and/or composition of the injection gas, and the pressure in the combustion zone. To ensure an inflow of water, the cavity pressure needs to be maintained at a level below the hydrostatic pressure. The syngas composition will change with time, depending on how long the reactor cavity has been on stream, and generally older reactors produce a poorer grade of product gas (Ahner, 2009). In most situations the aim will be to establish relatively stable conditions so that there will be consistency for periods of several days from an individual production channel. It can also be changed by blending the products from other reactors which have different syngas compositions.

Coal properties are important, and coal rank can be significant in terms of permeability, reactivity, water content and structural strength. In addition, if there is a high ash content there is likely to be a proportionately smaller surface area of char available to be gasified to CO. A primary property of concern is whether the coal swells or shrinks on heating. If it swells it could block the passages linking the injection and production wells. The ideal coals for UCG shrink and fall apart when heated, and this includes most of the lower rank coals. These will not block the necessary channels through the seam, and the breakup into smaller particles can provide a large surface area for the various reactions to take place. While there have been tests with higher rank bituminous coals, and even with anthracites, most have been for only short periods. Some Soviet work was undertaken in bituminous coals.

The coal seam depth will have a considerable effect on which technologies and techniques are used for establishing the connections between the injection and production wells. The proposed use of the syngas will determine whether air-blown or oxygen enriched systems are used.

The practicalities of UCG are dependent on the overall geology of a coal deposit, including the seam depth, inclination, and thickness. It depends crucially on the detailed geology of the overlying strata, and in particular the nature and strength of the rock formations above and possibly immediately below the seam, and the presence of aquifers. During UCG there can be substantial local thermal impacts which will affect the various layers near the reaction chamber which moves through the seam as the reaction proceeds. As gasification proceeds, an underground cavity is formed. The possible influx of water into the reaction chamber and gas leakage into the surrounding rock (which may be permeable) are factors which will affect the efficacy and applicability of UCG in particular strata. Water entering the cavity is likely to form steam and participate in the gasification process. Water use may lead to a drop in the local water table, but over time, when the gasification is complete, the water table should return to a level close to that existing prior to gasification (Perkins, 2005).

Reactor/process conditions Process parameters such as the operating pressure, gas outlet temperature and the overall flow rates are governed by the coal and rock properties, and by the nature and size of the linkage between the wells. Since these vary with time, the composition, temperature and pressure of the product gas needs to be constantly monitored since by observing changes it may be possible to deduce what is happening underground. The operating pressure is likely to be determined by the seam depth (see Section 2.3.2). One of the most important determinants of the design of an UCG facility is whether air is used as the primary oxidant, or enriched oxygen. The composition of the product syngas will vary substantially, and

26 IEA Clean Coal Centre the choice will affect flow rates and all equipment sizing. The intended use of the syngas will play a large role in determining the choice made although most set-ups will be designed to operate using air both on start-up and at various intermediate stages of the operation of the gasifier.

In the reactor cavity, the only oxygen source is that which is injected, and the burning/gasification direction always tends to move towards that source. This mechanism can determine how some linkages are made, and how the reactor behaves. In addition, heat always rises, and the two mechanisms can be used, both to understand and to control, what happens underground (Van der Riet, 2009). Because heat rises, in order to maximise energy recovery, reactions should normally be initiated low down in the seam, and where in-seam holes are used, they should be drilled as near as possible to the base of the seam. For the same reason, UCG should always be carried out ‘updip’ starting wherever possible at the lowest part of the seam to be exploited, even if the inclination/dip is small.

The operating pressure is a key parameter. The optimal pressure in shallower seams is probably the value at which the water inflow into the cavity is controlled at an acceptable level. This means that the reactions are confined within the coal seam and that the gasification products do not escape into the surrounding strata. In deeper coal seams, pressure balance considerations require higher pressures to control the influx of water. If the coal in deep seams is covered by an impermeable membrane of hard rock, then a reasonable balance between water influx and gas losses may be achieved. It may be necessary to supply supplementary water or steam. However, deep seams with high overburden permeability pose a potential problem in that the required pressure may be accompanied by unacceptable gas losses.

Both temperature and pressure affect the chemistry of gasification, and therefore the composition of the product syngas. For above ground gasification, the ideal temperature is probably in the 1000–1200ºC range, but it may not be possible to achieve this for much or any of the residence time underground because of the gas flow patterns, or because of local water influx.

In the reaction pattern illustrated in Figure 4, the high temperature zone is initially near the bottom of the injection well, although during the life of the coal seam section it will move along towards the syngas product exit well. Thus initially, there will be a higher proportion of unreacted pyrolysis products in the syngas, including tars and phenols. As the main gasification chamber gets nearer to the production well, the exit gas temperature will tend to increase, and the gas composition will change. This can be adjusted to some extent by changing the composition and/or quantity of the injected gas.

Once gasification operations in a section of the coal seam are finished the area needs to be returned to something like its original state in terms of the environment. This can be achieved by flushing it through with steam and/or water to remove any pollutants from the coal seam to prevent them from diffusing into surrounding aquifers. The ‘Clean Cavern’ concept for the end of a UCG trial has only been tested on a few occasions.

3.2 UCG methods

The basic UCG concept uses two boreholes, one for the injection of oxidants and the other for the removal of the product gas, see Figure 4 which shows one commonly used UCG layout. The oxidants react with the coal in a series of pyrolysis and gasification reactions to form carbon monoxide, hydrogen, methane, carbon dioxide and a variety of minor constituents. The transport of the gases between the inlet and outlet boreholes and their temperature and pressure controls the reactions. As shown in Figure 5, there are three stages in the life of an underground reactor. In the first, the permeable linkages are established between the wells. In the second the coal seam is gasified, and in the third the cavity is shut down and flushed through with steam and water, removing many of the more toxic by-products which might otherwise remain.

Younger coals such as lignite and brown coals may have sufficient permeability to enable a satisfactory connection between wells to be created over short distances (20 to 50 m), but most older coals are too compact or variable to rely on the natural fissures as pathways for UCG and the linkage has to be artificially ‘encouraged’.

UCG development has largely been concerned with: G designing underground pilot tests in appropriate strata, and in interpreting the results; G establishing methods to enhance the connection between the wells/boreholes in the coal with the intention of increasing the distance between adjacent holes, and/or reducing the time taken to establish the links (which can be several days, or even weeks); G for some of the methods, establishing the techniques for drilling accurate in-seam boreholes; G establishing methods for igniting the coal in the underground reactor; G controlling the process and the product syngas quality, and establishing monitoring methods; G ensuring a satisfactory level of resource recovery from the coal seam for a given configuration; G scaling up to commercial-sized operations, and reducing all the associated costs, particularly those of drilling.

Underground coal gasification 27 It has also been concerned with establishing the geological conditions in which it is environmentally safe to carry out the process, and the answers here will be different in different locations and coalfields. Attempts to generalise the criteria can be misleading. What is needed is a case by case assessment.

It is difficult/impossible to simulate many of the UCG conditions in a laboratory so pilot tests have to be carried out in the coal seams where large-scale exploitation is being considered. The use of laboratory simulations is discussed in Section 5.19.2 and they can be helpful when trying to understand the results from underground operations.

Pilot trials underground are expensive, as is the necessary prior exploration, and the results are not always easy to assess (DTI, 2004). The current position is that some successful trials have been carried out, notably at Majuba in South Africa, Chinchilla and Bloodwood Creek in Australia, and at Gonggou in China. The next stage in each case is to scale-up the operation to an intermediate demonstration-scale stage before expansion to commercial scale. This will take several years to achieve.

The mid-1990s onward has seen a resurgence of interest in UCG throughout the coal-producing world, and recent trials have established that viable solutions to the in-seam connection problem can be achieved in some places. Recent increases in the value of energy will have helped to promote the prospects for UCG.

Broadly, four generic methods for carrying out UCG using drilled boreholes/wells have evolved. They are: G vertical wells linked by hydrofracturing and/or reverse combustion; G vertical wells linked by an in-seam borehole; G using a Controlled Retraction Injection Point (CRIP) to move the place where the oxidant is introduced; G in steeply dipping seams.

The vertical sections of the wells are normally cased and sealed so that they do not interfere with the aquifers above the target seam and there is no gas exit path around the well on the outside. The discussion below uses material taken from Beath and Su (2003) and Beath and others (2004), and the methods are illustrated in Figure 6. These methods were all used in the trials which took place in the USA in the 1970s and 80s, and are discussed in Section 4.3.

It should be noted that the dimensions shown in Figure 6 particularly for well spacing, are only indicative and illustrative. The actual distances can vary substantially depending on the method of linkage, and the coal seam geology and permeability. The cost of syngas production is strongly influenced by the number of wells that are needed to extract a given amount of coal so increasing the well spacing is a significant driver when developing a UCG prospect.

In addition, ways of extracting energy from abandoned mines, and using man-made underground tunnels, have been developed in China which are discussed in Section 3.2.5. Some of the early work in both China and the USSR, looked at ways of developing UCG from existing mine workings.

3.2.1 Using LVWs with hydrofracturing This technique has been widely used and relies on two vertical wells, linked underground by using either high pressure air or water and/or by reverse combustion, to open up an internal pathway in the coal seam to facilitate gas flow between the wells. This is based on technology developed originally in the USSR, which has been used at Chinchilla in Australia and Majuba in South Africa. Vertical drilling is a commonly used and well proven drilling option in virtually all coal producing areas. It offers the possibility of using larger holes than in-seam drilling, allowing higher flow rates and therefore higher production rates then in-seam drilling. The techniques described in this section provide the basis for the ␧UCG technology used by Ergo Exergy Technologies Inc. Reverse combustion and hydrofracturing are discussed below in the paragraphs entitled Establishing underground linkages in Section 3.3.

In a typical arrangement, see Figure 6a, the basic link is between two holes, one for injection the oxidant (with air, oxygen-enriched air and/or steam) and the other for carrying the product syngas to the surface for treatment and use. The area in the coal seam affected by hydrofracturing is shown in Figure 6b, although in practice the shape of the fractured area may be highly irregular, depending on the particular weaknesses in the vicinity of the hole. For demonstration- or production-scale operations, a series of holes are used which are drilled in parallel rows, and this is discussed further in Section 3.3.1.

The technique is thought by some to be best suited to use in relatively shallow seams, probably in those <300 m deep. Typically the spacing between the holes is 20–30 m, although the first Linc Energy test at Chinchilla reportedly used distances of up to 60 m. The spacing will be dependent on the coal seam properties, and the ease or otherwise of establishing the necessary linkages. Seam discontinuities, dirt bands and faults can make the formation of predictable links more difficult. Hydrofracturing can produce unwanted passages or links for example along the boundaries between the seam and its surrounding strata.

28 IEA Clean Coal Centre a) Vertical wells b) The effects of hydrofracturing

high pressure 5-20 m applied here

linked by hydrofracturing and/or reverse combustion

plan view

c) Vertical wells d) Linear CRIP

no flow ~40 m >100 m

linked by an in-seam borehole

CRIP

e) Parallel CRIP f) In steeply dipping seams

>100 m ignition well

CRIP

Figure 6 The generic methods for UCG using drilled wells, as used in the US DOE trials (modified from Beath and Su, 2003; Davis, 2009)

The method has been thoroughly tried and tested over many years, mainly in the USSR, but with somewhat varied outcomes, and its application to any new UCG prospect is subject to a considerable degree of trial and error. It is the basis of the ␧UCG technology used by Ergo Exergy but since this is regarded as proprietary, few details have been published. Such technologies have a suite of options and a scientific strategy to select the correct one, although this involves successive trialling (Van der Riet, 2009). Extensive exploration and pilot testing will be required to assess the potential behaviour of the coal at a new site and the ease of making linkages between the holes. Before a commercial-scale operation can be costed and set up with any confidence a great deal of work is necessary including

Underground coal gasification 29 extended in-seam trials. The Majuba trials in South Africa using this technology are described in Section 5.15.1, and there are other developments such as that at Kingaroy in Australia.

3.2.2 Using LVWs with in-seam boreholes Advances in directional drilling have provided the basis for the construction of correctly positioned in- seam boreholes and are discussed in Section 3.3.2. The principle involved is shown in Figure 6c where the in-seam hole provides the physical link between vertical holes. It is potentially a much more certain and predictable method than using hydrofracturing and/or reverse combustion, provided that the holes can be drilled accurately so that they intersect and are adequately structurally stable. Links formed by in- seam boreholes are being used in a number of current and planned developments, including those by Promgaz in Russia, Linc Energy in Australia and Sasol in South Africa (see Chapter 5).

3.2.3 Using the CRIP configuration The third generic method uses a moveable injection point to determine the location of the underground reaction. The injection point is where the oxidant first comes into contact with the coal. The CRIP is determined/located by progressively burning away sections of a borehole liner. One method of doing this uses a burner on the end of a coiled tubing assembly which passes from the surface down the entire length of the injection borehole (see Section 4.3 and the write-up on Rocky Mountain 1). As the liner burns away, fresh/unreacted coal surfaces are exposed to oxidation and gasification.

The coiled tubing carries a fuel/air mix based on methane or propane which can be ignited by using a shot of silane or of triethylborane (TEB), both of which are extremely active polyphoric compounds. The ignition might be achieved by using an electrical spark, with appropriately designed equipment. The burner is located so as to burn through the required section of steel liner. When this has been done, the fuel supply is cut off, and the burner is retracted away from the high temperature zone where the coal is burning, in order to prevent erosion and other damage to the burner tip. When it is necessary to burn through a further section of liner, the burner is pushed forward to the required spot, fuel is supplied, and it is reignited. It stays in place only in order to burn through the further section of liner. When this is completed, it is again retracted away from the high temperature zone. This method was used at the El Tremedal trial in Spain, and at Rocky Mountain 1 in the USA (see Chapter 4). To facilitate burning away a section of the liner, the burner will probably be mounted on a circular support to place it somewhere near the centre of the hole, and the assembly will be designed to slide backwards and forwards fairly easily. Under some conditions where coal combustion near the injection point produces sufficiently high temperatures, some of the liner may burn away spontaneously, meaning that the use of the auxiliary burner may not always be necessary.

The CRIP was pioneered in the USA by the Lawrence Livermore Laboratory during trials in the 1980s. Its use has two potential advantages over other methods, as it can provide much greater control over where the gasification reaction takes place, and it will probably prove to improve resource recovery. It involves the drilling of far fewer wells from the surface.

There are two variants using this technique, see Figure 6d, known as linear CRIP, and 6e, known as parallel CRIP. There are some common features. In both, the injection well is an in-seam borehole which is lined with a thin steel casing to provide both mechanical stability in the hole and control of where the reactions are taking place. The oxidants (air or an oxygen/steam mix) are supplied from the surface through this lined hole and start to react with the coal where the lining ends. The mechanisms are discussed further in Section 3.7. Linear CRIP operation involves forming a series of reactors as in a batch process, while with parallel CRIP operation the reactor grows along/across the coal ‘face’ in a continuous fashion, until a whole panel of coal is used up.

3.2.4 In steeply dipping seams For gasifying a dipping seam (with >50º dip), angled injection and production wells can be used. The method was reported to have been used successfully in the USSR and was trialled in the USA (see Chapter 4). While steeply dipping seams are generally not possible to mine by conventional methods making them attractive for UCG, the geology of such seams is often complex, with unpredictable stress patterns, faults and gas leakage paths in the strata around.

The injection well should feed into the lower part of the seam while the production well should be in the lower third of the seam. It is advantageous to have the angled injection well penetrate the footwall (lower surface) of the seam to ensure that the injection point remains at the bottom. This is illustrated in Figure 6F. However as the reaction proceeds upwards, ash and char will fall into the initial cavity. A pool of slag will form at the bottom, promoting reaction of the char and increasing the efficiency of the gasification process. When compared with a near-horizontal seam where roof material may fall on the floor and remain unreacted as the reactions tend to move upwards, in a steeply dipping seam the char formed can fall into the molten slag and maintain the high temperature at the injection point. The high temperature zone remains at the base of the reactor. A coal ‘face’ is generated by the drying and

30 IEA Clean Coal Centre pyrolysis of the coal above. The cavity then moves up the seam towards the production well, while the main reaction zone stays in the molten slag at the base (Davis, 2009). Directionally drilled linkages between the wells would almost certainly be the most effective arrangement for its application on a larger scale (see Section 5.12).

Disadvantages to this technique are the specific seam characteristics required which limits the amount of accessible coal, and as the seam dips the hydrostatic head varies, increasing with the depth of the coal being used. This makes it more difficult to establish a water seal around the cavity and to prevent gas losses. The technique has been tested both in the USSR, and during the US DOE programme at Rawlins and later at Carbon County (see Section 4.3). It is described and discussed further in Chapters 4 and 5.

3.2.5 Using man-made excavations Some methods for UCG are based around conventional mining procedures, with shafts, drifts and roadways. There are several variations of these procedures, which have been used in China and the USSR. Some early European trials also used sites involving existing mines. The site is usually developed from mine workings using man-made galleries and links while areas of the mine are sealed off to prevent gas leakage. The different methods are illustrated in Figure 7, but are not now being actively developed, apart from the Chinese ‘long tunnel large section’ system discussed further in Section 4.4.

The chamber gasification technique is an extension of conventional mining where gasifiers replace working coal faces (Ökten and Didari, 1994). In China it is referred to as undersurface gasification (Creedy and others, 2003). The gasifiers consist of either shortwalls, longwalls or room-and-pillar systems. The gasifier chambers are sealed off before being brought into operation, while the mine roadways provide the access route for the pipes carrying both injection air and the product syngas. Operations take place at relatively low pressures, to minimise the risk of leakage. The syngas product commonly has a heat value from 4–6 MJ/m3 resulting from the use of air as the oxidant and the low reactor pressures. The techniques can be used to recover some of the remaining coal from a partly exhausted mine. Underground access is maintained at all stages of the operation.

In one procedure, the permeable links in a gasification chamber are created using explosives (see Figure 7a). In another method, linking holes are drilled underground across a coal seam from one roadway to another (see Figure 7b). The gasifiers are controlled independently from underground to ensure optimum performance. In yet another method used in the 1930s by Kirichenko in the USSR, the chambers were filled with crushed coal to facilitate good contact with the oxidant (air) in chambers which were surrounded by a masonry wall and sealed with tamped clay (Olness and Gregg, 1977).

A Soviet development, generally applied in steeply dipping seams, is called the stream method see Figure 7c. The injection and production holes were drilled into and along the coal seam and connected at the bottom by a mined roadway. The flame was initiated in the connecting channel and gradually spread along its entire length. The flow had to be reversed from time to time so as to get a roughly horizontal burn (Gregg and others, 1976). As the burn developed upwards, more coal fell into the reaction zone. Further panels were prepared for use once an area became exhausted. Using the stream method, the Soviets encountered significant flow distribution problems associated with roof collapse, and at some periods, severe gas leakage through cracks created by subsidence. The method has been developed to be used with drilled in-seam holes and in horizontal seams, both in Russia (see Section 5.12) and at Bloodwood Creek in Australia with the use of parallel-CRIP (see Section 5.1.2).

In China, considerable use has been and is being made of the long tunnel, large section, two-stage (LLTS) method, where the gasifier is constructed using mining methods, but is subsequently controlled from the surface ( see Figure 7d). The layout is similar to a conventional longwall mining district but with injection and production wells drilled at the gateroad ends. The gasifier roadway can be some 200 m long with a cross-section of 3–4 m2. LLTS methods seem to have commonly been applied to dipping seams. The work in China is discussed further in Sections 4.4 and 5.4.

3.2.6 Advanced technologies Three technologies are being promoted which might be best described as ‘futuristic’. They are untried and unproven, but have been publicised at recent conferences in various papers, or on their company website.

Texyn proposals An American company Texyn described their ‘Santa Barbara’ mining system in a presentation to the 2008 Pittsburgh Coal Conference (Tillman, 2008). It involves using a physical gasifier at great depth which injects steam into the coal seam. The principle is illustrated in Figure 8, and the aim is to exploit the vast coal resources in the USA which are more than 1000 m deep. These do not register in the proved recoverable reserves figures.

It is claimed that the system which injects guidable jets of steam will be able to gasify seams between

Underground coal gasification 31 a) Chamber method b) Horizontal boreholes between roadways

stopping coal pillar syngas exit SECTION injection syngas

horizontal borehole

air entry pipe blasted coal stopping entry coal seam exit

c) ‘Stream’ method for steeply dipping seams

boreholes PLAN air syngas overburden coal

horizontal boreholes

stopping

coal coal seam gallery drifts air and rubble entry surface boreholes exit

d) Long tunnel, large section two-stage method (see also Figure 20)

Figure 7 Methods involving man-made excavations and conventional underground mining (Ökten and Didari, 1994; Beath and Su, 2003)

3 and 30 m thick. It is said to be analogous to longwall mining, and it is intended that the ‘point and shoot’ steam jets will have the capability of shaping the cavity. The injection point will be progressively withdrawn, as with the conventional CRIP described in Section 3.2.3.

Because it is operating at great depth, it will be at high pressure (up to ten times that of a shallow UCG operation), and may even be able to operate at just above the hydrostatic pressure. Any nearby aquifers will be saline. The operating temperature may be as high as 1500ºC, and the intention is for the syngas to

32 IEA Clean Coal Centre injection well, 340l/m production well

potable aquifier

brine formation 1000 to 2700 m caprock layer brine formation caprock layer

caprock layer

gasifier

Plan view

pyrolysis zone production well char zone

guidable gasifier steam 30m production cavity ‘jets’

Figure 8 Texyn ‘Santa Barbara’ mining system (Tillman, 2008)

have a high CO and H2 content as CO2 and CH4 should be minimised under these conditions. Because of the high operating pressure, the CO2 present in the syngas should be separable and in the right state for storage, also at considerable depth. The Texyn plan envisages a pilot field test in 2010 with the aim of following this with a demonstration-scale project before commercialisation.

The super daisy shaft In a write-up on Polish activities in UCG, Palarski (2007) describes the ‘super daisy shaft’ concept. It is discussed in more detail by Moncarz (2008) where a pilot plant which would be built at Rybnik is described. The super daisy shaft is derived from oil industry practice, and is a ‘blind hole’ system with the steam and oxygen coming down the jet stingers, and the products coming back through the strata and up the shaft. They presumably ‘bore’ through the coal seam by creating voids as the oxygen and steam react with the coal. The shaft and layout are illustrated in Figure 9. It is claimed that it will potentially be able to recover syngas from an underground area as large as 15 km2. The shaft is 5.0 m in diameter with some 300–400 jet stingers and the technique has previously been used to recover heavy crudes. Its potential application for UCG is currently somewhat speculative.

In the ‘blindhole’ technique, having a multiple of single wells which provide the function of both the injection and production wells, the oxidant is injected through small tubes while the product is withdrawn through what may be described as its casing. The technique has been tested in the USSR, the UK and in China, mainly from already mined tunnels. It is obviously vulnerable to the possibility of the oxidant bypassing the reactive coal, which could result in a potentially dangerous mix of oxygen and combustible gases in the product syngas.

Underground coal gasification 33 A A

Section A – A

Figure 9 The super daisy shaft concept (Palarski, 2007)

Luca Technologies Luca Technologies, Golden, CO, USA, are investigating the ongoing biogenic production of methane in a number of large coalfields. The production is the result of indigenous populations of microorganisms which metabolise the large hydrocarbon molecules in coal into smaller hydrocarbons, principally

34 IEA Clean Coal Centre methane. The company describes these naturally occurring methane factories as ‘Geobioreactors’.

The company is undertaking a programme to understand and manipulate these microorganisms in order to ultimately maximise methane production in existing geobioreactors, and hopefully stimulate its production in currently non-reactive hydrocarbon deposits. The Powder River Basin basin deposits provide an appropriate initial target for the work. The traditional CBM extraction techniques entail pumping groundwater out of the coal bed, but this can allow the influx of air which is toxic to the methane-producing microorganisms. Thus Luca are looking at identifying active geobioreactors and measuring the rates at which methane is being produced together with mechanisms for enhancing production. The mechanism could be described as in situ gasification using a microorganism based process. If successful, it could either compete with, or possibly complement the UCG developments discussed in this report (Luca Technologies, 2009).

3.3 Establishing underground linkages

There are a number of ways of establishing underground linkages between the injection and production wells of a UCG operation. These include using: G the natural permeability of the coal and existing cleats and cracks (which may be enhanced by the application of hydraulic pressure, a procedure called hydrofracturing); G what are called ‘reverse combustion’ procedures, described below in more detail; G directional drilling in the coal seam which can either provide the main link between vertical wells and/or the basis for using the CRIP technique to control where the main underground reaction is taking place.

Other methods that have been suggested and tested to open up the necessary linkages in the coal seam are: G electro-carbonisation, where electrodes are placed at the bottom of both the injection and production wells. When these are subjected to a high intensity current, the coal heats up and carbonises, thus developing fissures; G the use of underground explosives for some of the cavern applications.

Directional drilling has been tested in Europe, the USA and in Australia (Singh, 2006) and active development is continuing, but more experience is needed in different coal seams. Directional drilling is discussed further in Section 3.3.2.

3.3.1 Hydrofracturing and reverse combustion The hydrofracturing and reverse combustion methods used in many of the USSR operations have the advantage that they can be considerably less expensive than in-seam drilling. However, the link may take unpredictable paths as it follows fractures and other routes which already exist in the coal seam.

At Chinchilla, the first trial took place using the ␧UCG technology with vertical wells linked by hydraulic fracturing and using reverse combustion (see Section 5.1.1). The second trial is thought to have used a directionally drilled hole in the coal seam as the primary link between the vertical injection well(s) and vertical production well(s).

At this stage of development, there is clearly an element of ‘trial and error’ in any testing which takes place. This is particularly true of using pressurised air or water fracturing to establish in-seam links, as it is difficult to predict where the fractures will go in a given coal seam. Once testing has been carried out and some experience gained, the element of unpredictability in a particular seam should be greatly reduced although seams do not necessarily have uniform characteristics over a large area. Both the hydrofracturing and reverse combustion methods can take many days (and possibly weeks) to achieve a satisfactory linkage.

Hydraulic fracturing Hydraulic fracturing has been widely used in UCG operations both in the USSR and more recently by the derived ␧UCG technology of Ergo Exergy. It has been used at Majuba in South Africa, see Section 5.15.1.

Hydraulic fracturing has been used in oil and natural gas production for many years. After a well is drilled into reservoir rock that contains oil, or natural gas, every effort is made to maximise the production of oil and gas. In hydraulic fracturing in this context, a fluid (usually water containing special high-viscosity fluid additives) is injected under high pressure. The pressure exceeds the rock strength and the fluid opens or enlarges fractures in the rock. These larger, man-made fractures start at the injection well and extend into the reservoir rock. Hydraulic fracturing allows the oil or natural gas to move more freely from the rock pores to a production well so that it can be brought to the surface.

In UCG, in order to break open and use the natural cracks and cleats in the coal, either water or air are

Underground coal gasification 35 used. Pressure applied down the injection well will tend to break open the cleats in a roughly circular area around the bottom of the well. When the fluid gets through to the production well, the water or air will flow through, showing that a passageway has been established. At this stage the pressure can be reduced, and the flow of oxidant started so that the reaction can be started.

The mechanisms involved are complex, since under stress (pressure) the cleats tend to close. Thus permeability is highly stress dependent. Generally the water present in coal is held in the cleats while any methane is held in the pore structure. When the seam is disturbed by the introduction of a borehole, the stresses change locally. When coal is mined underground the stresses are released, as is much of the adsorbed gas. Under UCG conditions, there are changes during the process of establishing the link between wells, and then when gasification is established, there are major changes in the coal as stresses are released and both the coal and surrounding rock are heated. As the link is established, the air (or water) pressure can be reduced as the low resistance path between the two wells is established.

Reverse combustion Reverse combustion linking (RCL) has been a widely used method for establishing a low resistance path from one well to another. It has been used in the past in work in the USSR, and is currently an integral part of the ␧UCG technology developed by Ergo Exergy Technologies (Blinderman and others, 2008a). It was first used at Podmoskovnaya (Russia) in 1941, and subsequently at Yuzhno-Abinsk (Russia), Lisichansk (Ukraine) and Angren (Uzbekistan) among other places. More recently it has been used at Chinchilla in Australia and Majuba in South Africa.

The procedure adopted is commonly as follows (see Figure 10): G an oxidant is injected into one of the two wells (well 2) under high pressure, and the coal seam is ignited at its base; G combustion of the coal near well 2 proceeds towards well 1 and the high pressure causes hydrofracturing, thus opening a linkage path; G the role of the wells is reversed, and the high pressure oxidant is injected into well 1 when there is a sufficiently clear link between the wells, the air/oxidant pressure can be reduced and the gasification of the seam can proceed; G the creation of a low resistance link between the two wells results in a significant drop in the pressure difference between them, indicating the successful completion of the linking process.

air air syngas (high pressure) (high pressure) syngas well 1 well 2

down hole electric heater

a) Wells drilled into seam b) Coal ignition c) Combustion front proceeds to air source

air air air (low pressure) syngas (high volume) syngas (high volume) syngas

d) Linkage complete when e) Combustion front proceeds f) Combustion front eventually combustion zone reaches in the same direction as reaches production well injection well injected air

Figure 10 The sequence of events in a UCG process using reverse combustion linking (Krantz and Gunn, 1982)

36 IEA Clean Coal Centre RCL is the opposite of Forward Combustion Linking a) reverse (FCL) where the coal is ignited at the base of the injection well and the fire propagates towards the production well air syngas (Blinderman and others, 2008b). The two methods are shown in Figure 11. It has been observed that links made between the wells made by FCL have a pear-like shape, as in the diagram, while those made by RCL are predominantly tube-like channels. The linking speed is overburden considerably lower when using FCL.

The RCL process was used in the first trial at Chinchilla in coal Australia (see Section 9.1.1). Nine process wells were ash flame successfully connected, with the spacing varying between 15 m and 60 m. Linking speeds between 0.9 and 11.3 underburden ignition m/day were experienced in essentially the same geological conditions and similar coal quality. This wide range suggests that the speed is highly sensitive to certain injection and production parameters and/or may be due to local variations in the cracks present in an apparently b) forward uniform coal seam. air syngas Both RCL and FCL involve the passage of air and product gas through the porous passages in the coal. They therefore involve coal devolatilisation, and chemical reactions in the gas phase as well as the combustion reaction between the oxygen present and the carbon in the overburden coal. Processes such as this, involving the passage and reaction of gases going through porous media are generically referred to as filtration combustion. In flame coal comparing the two techniques, it was concluded that in ash RCL combustion temperature is a critical factor affecting the flame propagation, but heat losses to the surroundings ignition underburden are less important than for FCL.

Although RCL has considerable operational advantages Figure 11 Schematic views of reverse and forward over FCL for establishing the necessary linkages, FCL can combustion linking (Blinderman and usefully be used for widening the hydraulic links between others, 2008b) wells which exist naturally or have been established using hydrofracturing (Blinderman and others, 2008b).

3.3.2 Directional drilling The most reliable way of establishing the link between wells is probably by using in-seam drilling and this is either planned or being done at a number of current developments (see Chapter 5). This can (in principle) achieve a pathway along the bottom of a coal seam. In-seam drilling was established at the Rocky Mountain 1 test in the USA in 1986/87 and more recently at Bloodwood Creek in Australia (see Chapters 4 and 5).

Drilling into coal seams from roadways and galleries is an integral part of modern underground mining, and is used extensively for exploration, the setting of explosive charges and the drainage of gas and water. The underground equipment is typically lightweight, easily mounted in roadways or at mining faces, and is capable of drilling unguided holes up to 200 m or more. The latest in-mine drilling equipment has an optional steering capability (DTI, 2005).

In the UK, in-seam drilling from underground roadways has been used for many years in existing mines: G to locate faults; G map seam gradient changes; G to drain water/gas before mining.

Drilling in-seam Drilling in-seam boreholes from the surface for UCG or for CBM production needs somewhat different skills and technology and is much less well developed than drilling from underground roadways. It requires the borehole to go down from the surface wellhead, and then to steer along a curved path into the seam, and possibly to follow a route in the seam for several hundred metres. A generic well design is shown in Figure 12, together with various alternative trajectories. Since coal properties vary widely, and the strata through which the drill is passing will have variable hardness, this presents a number of challenges. The interface between the coal seam and the roof and floor strata may also involve irregularities.

Underground coal gasification 37 a) Boreholes intersection

deviated injection well, vertical production well, surface section drilled completed at seam level vertical, then steered into to assist interception and along seam precise borehole intersection target seam depth ~ 600-1000 m

in-seam leg ~400 m

b) In-seam trajectories

planned trajectory

faulted seam

rolling seam

seam breakout

Figure 12 Directional drilling, the challenges underground with alternative trajectories (Jackson, 2003; DTI, 2005)

There is limited world-wide experience of drilling in-seam from the surface and this means that in many places it would be necessary to develop the skills, and that initially the costs could be high. Much of the existing experience is associated with CBM recovery, particularly in Australia and the USA, and in such places there can be an immediate application of the appropriate skills to UCG.

38 IEA Clean Coal Centre Guided drilling technologies have been used successfully for many years in the oil and gas industries but under rather different conditions from those encountered in a coal seam. Advances in down-hole measurement and communications technology, together with the location of guidance sensors directly behind the drill bit, have resulted in the development of a new generation of guided drills. These are capable of providing greater accuracy, higher drilling speeds and cleaner hole completions than earlier equipment could achieve.

Drilling a hole to maintain a line just above the base of a coal seam (which is a likely requirement) involves different constraints from those encountered in oil and gas drilling. The method selected will depend on the surrounding geological formations, their hardness, and the ease with which the hole can be lined and sealed. Surface to in-seam boreholes have been developed for methane recovery, but without the constraint that they need to get close to the base of the seam. If the drill breaks out of the seam going downwards it is more difficult to get it back on track than if it breaks out from the top of the seam, so drilling along a line near the base of a coal seam presents a technical challenge.

Despite more than ten years research and development into drilling and logging techniques, no generally applicable and reliable techniques have been established for the construction of in-seam wells (Jackson, 2003). The best results have been achieved with reverse circulation coring. This uses a solid bit (usually with a tri-cone) to produce a hole and to deliver rock/coal chips back for subsequent analysis. It is considerably faster and less costly than diamond drilling. However, if the pressure in the hole is not the same as that in the formation, there is the risk of collapse, which would trap the drill rods. Clay bands may become hydrated by the drilling fluid, and can swell, also trapping the rods.

Internationally, in-seam drilling has been used routinely by Sasol in South Africa to identify the location of dolerite dykes which disrupt production. This has used downhole motors with positional logging and mud-pulse telemetry. Some 350 km of in-seam holes had been drilled over a period of four years in coal which is some 200 m deep (Jackson, 2003). In both Australia and the USA it has been used in coals from 200–1300 m deep to explore the seams and drain CBM. There have been more than twenty projects with in-seam lengths of >1000 m.

The well design needs entry at a pre-determined location, and at an angle of incidence into the seam which allows the bit to remain in the seam. Unforseen faulting or gradient changes, or variability in the level of the seam floor can result in the drill head leaving the coal seam. This can be time-consuming and costly.

There are three main methods of maintaining the trajectory of an in-seam hole, and in order of increasing sophistication, are: G to use seam exits to determine the coal seam boundaries. At each exit the breakout is cemented and a new direction is established to follow the coal; G to establish the geometrical position of the coal seam by detailed exploration and steer by pre- programmed geometrical coordinates for the planned trajectory; G to use geological sensors adjacent to the drill bit to detect and follow the coal seam boundary.

Most in-seam drilling to date has relied on seam exits although the UCG wells for the Spanish trial at El Tremedal were drilled geometrically. Drilling using geological sensors is a method that has only been available since 2000. There is considerable experience of in-seam drilling for CBM recovery in both Australia and South Africa.

Compared with the situation when drilling for the exploitation of gas or oil, drilling in the vicinity of coal seams poses a range of additional technical challenges, namely: G coal seams are frequently much weaker than the strata surrounding most oil and gas reservoirs, and the mechanical stability of long in-seam holes is therefore an issue; G the precision requirements of drilling in a narrow seam are more onerous than those for most hydrocarbon projects, although the depth and operating pressure will be lower; G downhole casing equipment will be exposed to an aggressive chemical and thermal environment in UCG applications.

In-seam drilling needs to be preceded by extensive exploration, including a series of boreholes down to the deepest coal seam. The wells should be cored through the coal measures, and logged throughout.

In addition, seismic surveys should be carried out. 2D seismic has, at best, a resolution of around five metres at the depths under consideration, and several lines are required to eliminate errors and improve the correlations for topography and faulting. In 3D seismic, multiple linear arrays of geophones are located over the area and the source lines shot at right angles. It can produce a continuous geophysical image which can improve the resolution by a factor of three (to less than two metres) in areas where it works well. The advantages of 3D seismic have to be offset against the increased cost involved. An innovation in seismic surveying which might be useful for the assessment of seam continuity and the detection of small faults is borehole-to-borehole seismic. However, detonations in a well that has been drilled for injection or for the product gas in UCG can cause degradation and damage

Underground coal gasification 39 to the well which could limit its further use.

The same directional drilling equipment will be used for the build-up (vertical and curved) sections as for the in-seam drilling. However, the coal drilling will almost certainly involve a different drilling bit and modifications to the downhole motor settings and the geo-sensors. A change of fluid and of drilling conditions may also be required. Drilling in coal is a relatively rapid process compared with drilling in rock.

A wide range of drilling fluids with different mud contents are available designed to meet the operating and geological conditions in different strata. Water-based fluids are preferred on environmental grounds. Getting down to the coal seam depth is a conventional drilling operation, and the choice of mud weight and lubricity, as well as the reactivity and stability of the formations is part of standard drilling practice.

The entry point to the coal seam needs special consideration to avoid significant fluid losses. In addition, dirt bands above the seam can be reactive, leading to swelling and trapping of the drill string. Additives can be specified to minimise the problems of coal entry. Water is also the preferred fluid for drilling in-seam, and additives are avoided where possible because they can block the coal pores and prevent gas dissolution. The pressure balance at the drill bit is critical for borehole stability, and some additional mud weight may be unavoidable.

Steerable drilling assemblies are of two types: G rotary; G downhole motor with a bent sub-assembly.

A typical downhole assembly is shown in Figure 13, together with an illustration of the principles of both rotary and downhole motor steering. The top diagram shows an assembly using orientated gamma ray sensing located behind the drill bit which can detect the boundary between the coal and adjacent strata. The surrounding rock commonly has a higher gamma ray level than the coal. In the middle diagram, the schematic shows the rotary steering. Mud pumped down the drilling pipe rotates a turbine which in turn spins the drill bit. The mud carries back the material which is cut/excavated by the drill bit. If the drilling axis is slightly offset from the line of the drill pipe the borehole will curve in the direction of the offset. The bottom diagram shows the way in which the steerable assembly transmits power to the drill bit via the drill pipe. Positional sensors are linked to rams just behind the bit which continuously force the well in the required direction.

Rotary steerable assemblies are widely used in the oil and gas industries. Some have sophisticated computers providing closed loop control of the steering. Communication with the surface uses continuous electromagnetic telemetry as well as traditional mud pulses. Additional sensors measuring gamma rays in the rock or resistivity can be incorporated (as shown in Figure 13). They are designed for drilling lateral holes into oil and gas reservoirs over considerable lengths and at great depth. The offset angle which allows control of the steering normally has to be manually set at the surface by retracting the drill string.

For in-seam coal drilling, the downhole motor method with positional rams appears to have considerable advantages in terms of cost and effectiveness. It was used in the Spanish UCG trial. More experience is needed to ensure that drilling can maintain a hole in the required position in a coal seam without break- outs.

Other methods, such as coiled tube drilling which has been used by offshore oilfields in the UK, can be considered. This might provide a method of constructing in-seam branches, but consideration of its use in coal seams is at an early stage (DTI, 2005). The technology was used in the Spanish UCG trial to inject the oxidant (see Section 4.2).

The commercial development of UCG will probably require not only in-seam drilling but also the construction of multi-channel branches from vertical wells which only directional drilling can provide (DTI, 2005). So far, the test work undertaken has involved only single holes, and has been carried out on a fairly small scale, so the major contractors have limited experience of in-seam drilling.

One of the features of UCG is that the well configuration requires that the in-seam injection borehole intersects with a second well, in order to transport the syngas formed to the surface. A linkage between the wells is essential, and a physical intersection would make the linkage without other interventions. Homing devices have been developed for oil and gas exploration. Well-to-well ranging tools can be used to detect a nearby well through magnetic interference. In active homing systems a strong magnetic field is generated in one well which can be detected in the other. The maximum range is dependent on the conductivity and anisotropy (the directional properties) of the formation, and the mud used. Typically these devices can detect a casing string at a distance of about 30 metres. Intersects in a coal seam may be easier to achieve than those in the surrounding rock as the seam serves to focus the magnetic signal.

Proprietary systems for UCG intersections include:

40 IEA Clean Coal Centre telemetry package transmitting to surface

downhole motor drill bit

focused gamma inside collar

Rotary steerable drilling assemblies transmit power to the bit via the drill pipe. Positional sensors are linked to rams behind the bit which continuously force the well in the required direction

Figure 13 Downhole drilling assemblies (DTI, 2005)

G single wire magnetic ranging where a current is passed through a wire in the target well creating a magnetic field. This is picked up by the ‘measurement while drilling’ (MWD) system in the well being drilled. The MWD system is located near the drill bit to determine its position relative to the drilling table on the surface; G the generation of an alternating magnetic field by the downhole motor during in-seam drilling which is detected by transducers in the target well. A range of up to 60 m is claimed.

Intersections between wells, which is what is required for UCG will need precise knowledge of the separating distance between the two wells. The in-seam well must stop short in order to avoid destabilising or damaging casing of the target well.

3.4 Igniting the gasifier

This is a subject on which there is limited information which is probably partly because it is difficult to control and predict, and partly because some may regard the ignition method as proprietary knowledge.

Underground coal gasification 41 There is also a strong element of trial and error attached to the procedure as much depends on the exact conditions and geometry in the hole where ignition is being attempted as well as the condition of the coal and the amount of debris present. It is necessary to raise the surface temperature of the coal to the level where combustion can take place, generating enough heat for the reactions to become sustainable.

Gasifier ignition procedures are not particularly well discussed in the literature, and the information is fragmented. It is clear that seam ignition can sometimes take a considerable time, although provided seam permeability has been established, it seems that once started, the reactions can be satisfactorily maintained for many months, and even years. In the design currently being trialled at Bloodwood Creek in Australia, it is the intention that it will be some five years before the coal panel ignited in 2008 is exhausted. At Majuba in South Africa the UCG process is reported to have been running since January 2007 from the original ignition (Van der Riet, 2009).

Various methods have been tried. These include: G the use of pyrophoric compounds such as silane (SiH4 the silicon analogue of methane), triethylborane (TEB), and even sodium and magnesium. Flamable liquids such as diesel may be added; G methane or propane gas; G electrical ignition devices; G dropping hot coke down the hole; G spontaneous combustion of the coal with the injection of oxygen enriched air under pressure.

The following account of one of the trials at Thulin in Belgium (see Section 4.2) in a deep anthracite seam during the 1980s is instructive. From the outset, gasification took place by self-ignition in oxygen enriched air under high pressure. The enriched air was kept under 10 MPa pressure in the hole for twelve days to induce spontaneous ignition in the coal. The injected flow was then increased, and the oxygen enrichment decreased. During the first month the gas produced contained a large amount of methane, and resistance to gaseous flow through the char formed increased. The injection pressure had to be steadily increased to 28 MPa, while the cocurrent gasification process in the gallery link developed into a process of countercurrent filtration gasification. Two other gasification agents were tried out, namely air, and a mixture of oxygen and foamy water (Dufaux and others, 1990; Chandelle and others, 1989).

At the Rocky Mountain 1 test (see Section 4.3), one of the last in the US DOE programme, the igniter system was flushed through with nitrogen at a pressure of 0.15 MPa above the downhole pressure. Then: G the air injection flowrate was established through the well casing to establish a system back pressure; G with the igniter isolated, the low pressure silane bottle as filled to the pressure required to deliver 1.5 tube volumes of silane at downhole pressure; G the silane was then injected into the well, and the igniter tip thermocouples closely monitored; G methane was then supplied by slowly opening the supply valve; G when the methane reached the end of the igniter tubing an increase in the thermocouple readings was seen, and the CH4 flow increased; G the methane gas flow was maintained until the thermocouples became very hot and the product gas analysis indicated that good combustion was being achieved, with no residual oxygen present (US DOE, 1989).

It is reported that various methods of igniting the injection air underground have been tried, including magnesium (as used in flares), and phosphorus, but there is no public information about what method has finally been established.

3.5 Monitoring

In their review, Burton and others (2006) highlighted the fact that the monitoring of UCG is in its infancy. There remains substantial potential for improving the monitoring and possibly the control of the underground reactor processes. The current pilot projects in Australia and South Africa, and other imminent projects like the one in Wyoming in the USA, could benefit substantially from comprehensive monitoring aimed at improving the understanding of the in situ gas formation and reactions, and of aqueous movement near the reactor zone. This will become increasingly important as the pilots expand to demonstration-scale as discussed in Chapter 5.

So far, the monitoring of UCG trials has been quite limited. Usually it has involved placing thermocouples in monitoring wells above shallow burns. There have also been some attempts to test elecromagnetic induction tools. At both Chinchilla and Bloodwood Creek in Australia, the burn area has been surrounded by around twenty wells which monitor the groundwater pressure and composition. At Bloodwood Creek these were located alongside the burn area on either side and at three different heights, above, level with the burn, and underneath it.

42 IEA Clean Coal Centre The only parameters which can be monitored are the gas composition, pressure and temperature going into the injection well, and the same information about the syngas produced. No UCG project has been monitored in a way which would give any detailed process control information or to show the evolution of the in situ reactor. Inferences can be drawn when, for example, oxygen slips through and is detected in the syngas or when the injection gas composition is deliberately changed.

The possibilities of developing a monitoring capability, possibly integrated with the development and validation of the various models being developed, are discussed in Chapter 6.

3.6 Well design and operation

UCG involves the drilling of a substantial number of wells and in-seam holes. UCG operating conditions require that the injection and production wells can withstand the thermal and mechanical stresses associated with UCG. Under some operating conditions their roles are reversed, so that either well may take the hot product gases. The wells cut through widely differing kinds of strata from hard rock to permeable sandstones and clays. They may cross underground aquifers. The linings need to be capable of withstanding corrosion from oxidation reactions, and from the gasification products, including both sulphur and chlorine-based by-products. If the UCG infrastructure is subsequently used for CCS operations, then the well materials must also be able to withstand the corrosion associated with CO2 (Burton and others, 2006).

Well integrity is essential in order to protect the groundwaters and to provide some control of the combustion processes. The construction materials and lining used need to be able to withstand the elevated temperatures involved and be resistant to corrosion from a variety of constituents on the gases. Some of these may arise from impurities in the coal. The testing of the mechanical integrity of the wells being used is recommended both at the start of a project and at regular intervals during UCG operations (Burton and others, 2006).

Wells are usually cased with carbon or high-strength stainless steel. They are normally cemented above the level of the reaction zone to facilitate the controlled introduction of the oxidant (air or oxygen- enriched air, possibly with steam), and to prevent the loss of product gases into the overlying strata. The well lining should also reduce the influx of water from surrounding strata. The wells need to withstand the operating pressure used and to retain their integrity when the ground around them moves. Where hydrofracturing is carried out, the wells need to be able to cope with the pressures used. Wells should be sited to avoid locations where rock deformation and movement could affect the casing integrity. The possibility of subsequent ground movement and subsidence needs to be considered.

The pressure at which the oxidant gases are injected into the seam is a key to controlling the combustion/gasification processes and to preventing the uncontrolled loss of gases and contaminants from the reaction cavity. Maintaining an appropriate flow rate is also important, as is the gas composition of the oxidant (consisting of air or oxygen enriched air, possibly with some steam). If the temperatures in the reaction cavity are maintained at a sufficiently high level, many of the organic contaminants will be broken down.

Cavity growth around the wells themselves is quite difficult to control, and this is something that can easily affect well integrity, possibly because of collapse of the adjacent roof material which is likely to affect the gas flow patterns. It will become easier to predict and control as more operating experience is gained. The effects will be quite different in the case of the use of vertical wells with enhanced seam permeability established by hydrofracturing or reverse combustion and the use of long in-seam holes with a CRIP. The in-seam holes carrying the oxidant will almost certainly need to be lined, either with a steel which will burn away at the temperatures generated at the CRIP, or possibly, in some formations, using a plastic sleeve. The integrity of both the injection and production wells/boreholes needs to be maintained so that the CRIP can be progressively moved.

3.7 Operating with a CRIP

CRIP operation is based on the fact that the injection point for the oxidants into the reaction cavity is at the end of a lined in-seam borehole, and the lining is progressively burned away, thus moving/retracting its location. This was described briefly in Section 3.2.3.

In what is known as ‘linear CRIP’, the injection well for supplying the oxidant, is an in-seam borehole (as described above), while the production well taking away the syngas, is a vertical hole drilled to intercept it. In linear CRIP, ignition is initiated at a point near the production well. Once the coal nearer the production well becomes exhausted, the CRIP is moved along the seam in step-wise movements, as the liner is burned away using a burner near the centre of the borehole. A new gasification cavity is initiated after each movement and thus fairly close control can be achieved. Gasification is carried out in a succession of cavities and thus it can be described as a batch process. It operates in a forward

Underground coal gasification 43 combustion format, and the product syngas passes through the ‘spent’ cavities and over an increasing distance as the CRIP is withdrawn, before reaching the vertical production well. The method was trialled at Centralia in the USA and in the Spanish test at El Tremedal (see Chapter 4);

In the second arrangement known as ‘parallel CRIP’ two in-seam holes are drilled in parallel in the lower part of the seam, and then turned near the end to meet at a point, maybe as much as 500–700 m from where they started. Where they intercept, a vertical well is drilled, which is used to facilitate the ignition of the underground gasification reactions. The seam is ignited at the base of the vertical well and the air flow established from the injection well to the vertical well, drawing the fire to the end of the liner. When operating, one of the in-seam holes is the injection well, and is lined (as already described). The CRIP movements are dependent on the burning away of the liner, which can be carried out as described above for linear CRIP, using a burner, or the liner may burn/retract as part of the process if the temperature at the injection point is high enough. This might be controllably achieved by either increasing the oxygen content of the oxidant in the injection well, temporarily increasing the flow rate, or possibly by increasing the oxidant’s temperature. This is not something that has been discussed in the published literature at the time of writing. The other in-seam hole is the production well, carrying the syngas product to the surface, and this needs to be stable enough to carry the hot syngas which will trigger some pyrolysis in the coal forming the well ‘wall/sides’ as the coal heats up.

Once the seam is burning sustainably the product gas flow is directed up the production well. The vertical well is sealed and used only to monitor reactor temperatures and pressures.

The parallel holes can be several hundred metres long, and the gasification proceeds across what might be described as a coal ‘face’. As the CRIP is moved progressively, the gas flow moves steadily away from where the ignition well is sited, and streams across the ‘face’ bypassing the cavity formed earlier in the cycle. This operational mode is known as ‘streaming’ gasification, and is the same as that employed earlier in the USSR (see Section 4.1). This method was used at Rocky Mountain 1, in the USA, and is currently being trialled on a larger scale at Bloodwood Creek in Australia (see Section 5.1.2), where the 30 m wide coal panel being gasified could last for up to five years before it is exhausted. It thus involves a higher start-up cost that the other CRIP arrangement, with two long in-seam holes, but once started should involve a lower operating cost, and produce gas more efficiently.

In-seam drilling is sufficiently well established in some countries that holes up to 1.5 km long can be drilled. The expertise is generally available in countries where coal seam methane is recovered as this is dependent on in-seam drilling, albeit with a different objective.

With linear CRIP a series of cavities is formed, as illustrated in Figure 14 where the upper part of the diagram illustrates the pattern which develops during a test using a single hole while the lower part illustrates the effects which would result if the method were used on a commercial scale using in-seam holes. A number of parallel CRIP ‘faces’ would produce cavities with a different and more regular shape. Coal seam pillars could be left (as shown) to reduce the amount of surface subsidence. The technique is discussed further in Chapter 4, while parallel CRIP is discussed in Section 5.1.2.

3.8 Shutting down a UCG reactor

When an UCG operation is to be closed down, appropriate shut-down procedures are essential to prevent the uncontrolled escape of toxic by-products and the subsequent contamination of underground aquifers. In recent work, particularly that at Rocky Mountain in the USA, and at Chinchilla in Australia, the concept of leaving a ‘clean cavern’ has been developed and tested, although experience with the technique is very limited, and will remain so until further work is done on the current pilots (see Chapter 5).

The procedure involves flushing through the cavern with steam at the end of its life, and carrying off many if not most of the possible contaminants present for treatment on the surface. In addition, the water which will flood the cavity when the pressure is removed can be pumped out as necessary on a planned basis and cleaned up if that is necessary. Both during operation and after shut-down, water quality will be monitored to check: G its pH (alkalinity); specific conductance; turbidity and temperature; G the amount of total dissolved solids (TDS); total organic carbon (TOC) and amount of suspended solids (USGS, 2008); G concentrations of possible toxic contaminants such as phenols, cyanide and boron.

If it does not meet required standards at a particular location, the water in the cavity can be pumped out again and treated, possibly with gaps of several months, or even years between such operations. This kind of procedure will become a routine part of the risk management strategy as more UCG operations are undertaken.

44 IEA Clean Coal Centre Linear CRIP reactor for initial trial

production well injection gases

cavities

Multi-channel linear CRIP reactors for commercial-scale operation

Figure 14 The progressive formation of new cavities as the CRIP is moved away from the production well (modified from Beath, 2004)

3.9 Summary and discussion

The techniques most likely to be applied in new UCG tests are variants of: G the vertical wells method used extensively in the USSR, and more recently at Majuba in South Africa as the Ergo Exergy ␧UCG technology, in conjunction with hydrofracturing, electrolinking and/or the application of reverse combustion to establish the necessary links; G the vertical wells method with in-seam drilling to establish the links; G the CRIP configuration in an in-seam injection well in conjunction with a vertical production well; G the CRIP method applied in two parallel wells with a vertical ignition well, making use of the ‘stream method’ in a near horizontal seam, as used recently at Bloodwood Creek in Australia; G a combination angled footwall/underseam entry injection wells and in-seam production wells carrying the syngas would typically be used for a steeply dipping seam (see Figure 6f); or G a Chinese development used with man-made mined tunnels called the long tunnel, large section and two stage method.

The vertical wells method is relatively simple in operation. A number of holes are drilled and cased at regular intervals in a grid formation. These may typically be between 20 m and 30 m apart, depending on the ease or otherwise of establishing the underground linkages. Linc Energy reportedly used distances up to 50 m without difficulties, but the gap is dependent on coal seam permeability and moisture content.

Underground coal gasification 45 Gasification proceeds by the injection of oxidant gas into one row of holes while product syngas is extracted from the next parallel row of holes. When oxygen is detected in the product gas a new row of product gas holes further away is commissioned in order to expose new coal to gasification. Variations in the selection of product and feed holes within the grid can be used to adapt to changes within the gasifier chamber(s) caused by blockages (due to roof collapse) or variability in reaction rates in different parts of the block. This variability can be due to variations in the seam or, more likely, by differences in the surface area of coal and char which is exposed locally.

The vertical wells approach is probably more appropriate for relatively shallow coal seams, <300 m deep, as the grid of regularly spaced wells becomes increasingly costly at greater depth. However, one current trial is at 1400 m deep, see Section 5.3. Vertical wells can be readily used with either air or oxygen as the oxidant, and the choice will depend on the eventual products to be produced from the syngas, and whether the presence of diluent nitrogen is a disadvantage. When air is used as the oxidant, the syngas will have a reduced heating value, but the (substantial) cost of building and operating an air separation unit (ASU) is avoided.

By comparison, the CRIP-type method is likely to be more applicable in deeper seams as the higher cost of the wells is compensated for by the reduction in the number of wells needed. The configuration with the vertical production well near which the reaction is started, has an inherent problem, in that the product well is located in the low point of the reactor. Water and debris are likely to collect in the vicinity, possibly blocking the flow of product syngas through the reactor cavity (Davis, 2009).

In an alternative configuration, two parallel in-seam holes may be used. These may be some 20–30 m apart, although in appropriate circumstances, this distance may be increased. One hole is used as the injection well, and is lined with a burnable material as described above. The injection point is retracted either by inserting a burner to melt a pipe section, or continuously by the destruction of the liner by the burning of the coal. The parallel CRIP develops a reaction zone along the coal ‘face’ which moves steadily away from where the ignition well is located, with the product gas flow bypassing the dead- volume of the spent reactor cavity. This is discussed further in Section 5.1.2.

The CRIP method is more dependent on the long-term integrity of individual holes, and casing failure has been a fairly common fault during UCG tests in the past. It is also limited by the pipe size it is possible to drill in-seam and the greater length of (accurate) in-seam drilling required. The gasification rate may be limited by the permissible diameter of the product well as the volume of the product gases is considerably greater than that of the injected gas.

With both vertical wells and the CRIP method it is typically desirable to delineate an area of coal and to gasify it as completely as possible leaving only small pillars of coal in between the blocks to isolate the different cavities during operation (Beath and others, 2004). Only with some prolonged operating experience will it be possible to confirm the practicality of doing this on a large scale.

In a steeply dipping seam, a footwall entry injection pipe (under the seam) is used while the product pipe is an inclined in-seam borehole. The injection well should end in the lower part of the seam while the product well should be in the lower part of the seam. Once the coal is ignited, a cavity will form at the base of the injection well, and will grow upwards while the dry pyrolysed coal falls to the bottom of the reactor cavity. A pool of molten slag can collect at the injection point and is the site of the primary oxidation of the fine coal char, and the generation of the high temperatures that drive the process (Davis, 2009). The technique is highly site specific, and if it is required to extract energy from deeper parts of the seam, drilling costs will increase, but it may also be possible to operate at a higher pressures. However, the configuration is prone to gas losses along the bedding planes of the seam up to the coal outcrop.

There are about a dozen sites which use the Chinese LTLSTS method. They typically use 2 m square underground tunnels with around 200–300 m long sides and ‘face’. The wells to the surface are around 1.5 m diameter and can be used both to carry the injection gas, and also the syngas product in addition to providing access. The product gas is of relatively low grade.

Gasification can be performed in two stages, with two distinctly different product gas mixtures.

Oxidant selection As with surface coal gasification, UCG can use either air or oxygen as the main feed gas. In surface gasifiers there has been a trend to use oxygen because the size of the gasifier can be reduced with considerable savings in capital cost in spite of the requirement for an ASU. With UCG the use of oxygen will depend largely on what the syngas is going to be used for, and whether or not CCS is required.

For large-scale facilities with well fields covering a big area, it has been suggested that oxygen may be justified based on the cost of transport to a central collecting station, of the diluted (lower heating value) air-blown syngas. For electricity generation the presence of nitrogen may be valuable for use in a gas turbine because of its mass. Its presence will be a cost factor if carbon capture is required after the

46 IEA Clean Coal Centre combustor. Oxygen-blown syngas product is likely to need dilution before entering the combustor so as to reduce the combustion temperature to that of the operating limit of the gas turbine.

There will be differences in the design of air and oxygen-based UCG systems as the metal components of an oxygen system must be of higher grades, but pipe diameters can be smaller, thus reducing drilling costs, particularly of directionally drilled in-seam holes. Operationally, oxygen-blown systems typically run at higher temperatures, so the higher hydrocarbons are likely to form simpler compounds, and the tar content of the product gas will be lower.

Operating methods The methods used not only affect operational performance but also the environmental performance of a site. Obviously the feed rates and composition of the injected gas into the gasifier will impact the gas production rate, gas quality and the coal consumption rate. What is affected includes the gas velocities, the temperature variations underground in different parts of the chamber and the chamber shape as well as any progressive collapse of the roof into the cavity which has been formed.

What has clearly emerged for the trials is that the operating pressure underground is an important variable. Excessive pressures have been linked to the contamination of surrounding groundwater with organic by-products of the process as well as reduced process efficiencies due to the loss of product gases.

Current best practice operating conditions that have been generally adopted include: G ensuring that the gasifier operating pressure does not exceed the hydrostatic head at the coal seam, thereby restricting any losses; G the ‘clean cavern’ concept when the gasifier is shut down which ensures procedures such as purging with steam, to flush out any accumulated organics from the cavity together with the pumping of any accumulating water for a period after shut-down (as discussed in Section 3.8).

Coal quality The nature of the coal affects the process, but not in any fundamental way. Low rank coals may have such a high water content that it interferes with the reactions and with the product syngas quality, especially if water also flows into the cavity from surrounding strata. High rank coals may have poorer ignition properties, and much of the more successful work to date has been with subbituminous or high volatile bituminous coals. In addition the structural strength of the coal seam will have an effect both on the stability of any borehole through it, and on the way the roof collapses into the cavity.

Resource recovery With a well designed and operated setup, the overall recovery of coal from a target gasification field could be in the range 80–90%, depending on the structural requirements for leaving pillars between the panels. Of the coal gasified, the cold gas efficiency (the recovery of the coal energy in the gas) should exceed 75% for an oxygen-blown process, and 65% for an air-blown process (Beath and others, 2004). Much more work is needed to establish the levels of resource recovery in practical situations and in large-scale operations and this information will emerge as demonstration- and commercial-scale UCG is carried out in the coming years.

Underground coal gasification 47 4 The main trials

The major trials of UCG which have taken place in the past in the USSR, in Europe, the USA and in China, are discussed in this chapter in that order. Broadly, the tests and developments which took place before the year 2000 are discussed in this chapter.

The current efforts to bring UCG to commercial-scale development are discussed in Chapter 5. Test and development work is currently taking place in Australia, Canada, China and South Africa. There are active proposals for development in a whole range of other countries, including India, Russia, the UK and the USA. Some of the Chinese work which took place in the late 1990s is considered in Chapter 5. Similarly a brief outline of the test in New Zealand in 1994 is included in Section 5.10.

The main UCG trials are described here in some detail, with references provided to more detailed assessment documents about the results obtained and their limitations, because slightly too much has been made of the fact that the process has ‘been tried and tested for more than fifty years’. Another way of looking at it is that it has taken more than fifty years before viable pilot tests have been carried out which have the potential for development to demonstration- and commercial-scale operations. There are useful reviews in: G Historical development of underground coal gasification (Olness and Gregg, 1977) G UCG history (Beath and Davis, 2006); G Review of environmental issues of underground gasification (Sury and others (2004a); G Best practices in underground coal gasification. Draft (Burton and others, 2006).

While each of the trials may have discovered something new about UCG, and most were useful in one way or another, each test rarely ‘proved’ or established more than one aspect of the technology, and many encountered unwanted side effects. Much of the work in the USSR was inadequately reported, and there have been translation difficulties in interpreting some of the accounts which exist. While more recent test work has been more comprehensive in establishing the necessary conditions for possible demonstration-scale activities, there have been relatively few published results.

Establishing the necessary conditions for carrying out an UCG trial has often taken many years, since there are several lengthy stages. The currently proposed trial in a panel of coal under the Firth of Forth in the UK has been under active consideration since 2002 (DTI, 2006).

The preliminary steps for setting up a trial may take from one to two years and subsequent stages may take two or even three more years. They typically include: G scoping the proposed project, and selecting the potential site which could support a commercial- scale development; G getting preliminary finance in place as well as planning permission and permitting; G exploration work to get a detailed assessment of the strata involved underground; G planning and building the surface installations, including storages, office and laboratory facilities; G getting the necessary equipment and materials to the site and drilling the (initial) wells; G installing the necessary sensors for monitoring changes in the surrounding rock formation, and in the groundwaters; and for monitoring the movement of the gasification reaction in the seam; G investigating the seam/deposit permeability, and establishing the linkage between the wells; G initiating ignition and carrying out the gasification trials under a variety of conditions, generally in line with a pre-planned programme. In some cases, this key stage has lasted only a matter of days even though the overall process has taken years; G monitoring all the process variables possible and any environmental impacts; G the test results need to be thoroughly assessed and a formal report prepared to cover all aspects and provide the basis for a feasibility study of the prospects for expansion of the project to commercial- scale.

Trials and experiments have been carried out in different strata, and at different depths, see Figure 15. This illustrates the priorities in Europe (where the interest is mainly in deep unmineable bituminous coals, sometimes lying in relatively thin seams) compared with those in the USSR, the USA and Australia who have all been interested in shallower deposits, of which a high proportion have been of lower rank coals (particularly of HV bituminous and subbituminous coals). The amount of work carried out in deep seams is very limited.

The detailed discussion of some of the conditions used illustrates the coals and coal deposits tested, but each test may establish just one or two aspects of the technology. Problems have been encountered during some tests, and on a global basis, the trials have only been carried out in a limited number of geological settings. A good proportion of the test work has been carried out in lower rank coals which have greater permeability and a higher inherent water content. Different methods of establishing linkage between the injection and production wells and different ways of igniting and controlling the underground reactions have been investigated, together with the use of different oxidants.

48 IEA Clean Coal Centre increasing surface interaction increasing drilling cost and operating pressure 30 2

Eastern Europe and USSR / m 3 25 Western Europe, Africa and UK USA China 20 Australia and New Zealand increasing resource m resource increasing 15

10 Mean seam thickness, m

5 more uniform more water influx 0 0 200 400 600 800 1000 1200

Mean seam depth, m

Figure 15 Coal seam thickness and depth for the various field trials of UCG (Perkins, 2005; Beath and Davis, 2006)

4.1 In the USSR

The USSR had a long-standing interest in UCG as it was seen as a method of getting the energy from coal without putting workers at risk underground. Since most of the work was undertaken in Soviet times, the geographical reference to the USSR seems appropriate, even though it broke up at the end of 1991 into a number of independent countries. Much of the work was in what is now Russia, although there were also significant projects in the Ukraine, and an ongoing operation at Angren, in what is now Uzbekistan.

In an Overview of the Soviet effort in underground gasification of coal (Gregg and others, 1976) and Historical development of underground coal gasification (Olness and Gregg, 1977) there is a concise history of the developments in the USSR up to the mid-70s. The first field experiments were carried out in 1933 using the chamber method with man-made underground cavities providing the underground reactor space, suitably sealed from the rest of the mine. These were followed by a series of trials and industrial-scale operations using the LVW method during which the linkage methods discussed in Section 3.3 were developed. In the 1960s there were several thousand people working on UCG, but the effort was reduced dramatically in the early 1970s, probably due to the discovery of large natural gas resources.

The Soviets demonstrated that they had a system which could be operated repeatedly in a predictable manner and transferred to places with different geological settings. In spite of this, the total amount of coal gasified was only some 15–17 Mt. The largest amount gasified has been some 10 Mt at Angren, and about 2 Mt each at both Yuzhno-abinsk and Podmoskova. Operations in the USSR were not carried out with the kind of environmental sensitivities (or regulations) that a modern UCG development would be subject to. In addition, the economic criteria applied would have been completely different from those that would determine current developments. As a result, the findings are of limited value in relation to ongoing assessments. Brief details of the tests are presented in Table 2.

Most of the sites using air as the oxidant produced a syngas with quite a low heating value, in the range 3–6 MJ/m3. Where oxygen or oxygen-enriched air was used the heating value was generally in the 6–10 MJ/m3 range. There were significant gas losses due to leakage, and commonly between 5% and 25% of the gas formed was lost from the underground gasifier. In an overview of the Soviet experience,

Underground coal gasification 49 Table 2 Summary of past experience with UCG in the USSR (Beath and others, 2004)

Seam Seam Syngas CV Test Year Coal type Technique Oxidant thickness, m depth, m MJ/m3

Krutova 1933-35 brown chamber 2.5 15 air 4.14

Shakhty (Russia) 1933-34 anthracite chamber 0.38 n/a air 3.87

Krutova 1933-35 brown chamber 1.75 20 air 4.14

Leninsk-Kuznets 1934-36 bituminous stream 4.85 28 air 10.04 (Kazahkstan) Lisichansk 1934-63 MV bit chamber 0.4 400 oxygen 3.21 (Ukraine) Lisichansk 1934 bituminous chamber 0.75 24 air 3.78 (Ukraine) Lisichansk 1934 bituminous single VW 0.75 24 air 3.77 (Ukraine) Lisichansk 1934 bituminous single VW 0.75 24 oxygen 10.46 (Ukraine) Gorlovka 1935-41 n/a SDB 1.9 40 oxygen 5.83 (Ukraine) Gorlovka 1937-39 n/a SDB 1.9 40 air 3.95 (Ukraine) Gorlovka 1937-39 n/a SDB 1.9 40 oxygen 5.82–10.34 (Ukraine) Podmoskova/Tula brown high 1940-62 VWs 2 40 air/oxygen 5.92 with O (Russia) ash 2 Lisichansk 1940-41 bituminous stream 2.7 138 air 2.57 (Ukraine) Yuzhno-abinsk LV bit low 1955-89 SDB 2 n/a air 8.8-12.1 (Siberia) ash Angren brown low 1962-89 VWs 4 110 air 3.5-3.9 (Uzbekistan) ash Shatsky brown high 1965-74 VWs 0.3 11 air n/a (Ukraine) ash

The data on the tests is as published, and may not be entirely representative of the site operations over the period. In particular, some Soviet sites operated for long periods under a range of conditions and those included in the table represent only a snapshot of one or more of the sets of operating parameters used. Naming some of the tests has presented some difficulty as some researchers have given different names to the same tests, and there have been some problems arising from the need to translate the technical papers written chamber mined tunnels around an explosively fractured block of coal stream where the gas flows across a reacting coal face VW where the product is taken from the same vertical well as the reactant. VWs where there are several vertical wells SDB steeply dipping bed

Kreynin (1993) comments that the UCG process remains unstable and inefficient in terms of thermal power. The controllablity of UCG using the traditional LVWs method is achieved by a large number of wells being brought into operation, and new ones are used as the heating value of the product syngas decreases. This simultaneously causes disorganised hydrodynamics in the underground reactor cavity, and unpredictable flows of the oxidant and combustible components. As a result, there can be combustion of some of the syngas formed. Recent Russian UCG design (see Section 5.12) seeks to tackle these shortcomings.

While there was work at a considerable number of sites, the main ones were at: G Gorlovka in the Ukraine where some early work in a steeply dipping seam tested out the advantages of using an oxygen enriched oxidant compared with air; G Lisichansk, in the Ukranian Donbass coalfield. The coal was bituminous with 6–16% ash, and thin (0.4–1.5 m) seams down to 400 m, some dipping steeply. The early trials were in the shallow part of the seam; G Yuzhno-Abinsk, in the Kuzbass coalfield. The coal was bituminous with 4–10% ash, and up to twenty-three seams 2–9 m thick, dipping steeply;

50 IEA Clean Coal Centre G Podmoskova, in the Moscow basin. The coal was a lignite, with 27–60% ash and 20–30% water. It lay horizontally in seams 2–4 m thick and 40–60 m deep; G Angren, in what is now known as Uzbekistan. The coal was a lignite, with 11% ash and 30% water. It lay with a dip of some 5–15º in a seam 4–24 m thick, and depth 110–250 m.

In one of the earliest schemes (at Lisichansk in the Donbass region), the first attempts involved men underground using the chamber method ( see Figure 7a) with explosive fracturing and excavation to link the wells, and later underground drilling was used to make the link. The area was sealed off and the flame initiated in the connecting channel.

The method which the Soviets thought had most promise in the 1930s was the stream method, for gasifying the coal in steeply dipping beds. It was tested at Lisichansk in the Ukraine and at Leninsk- Kuznets in Kazakhstan. This is shown in Figure 7c, and described in Section 3.2.5. The stream method is now being successfully used in a horizontal seam at Bloodwood Creek in Australia (see Section 5.1.2).

The projects later achieved successful gasification using only remote access (with drill holes or wells going to and from the surface). The Soviets achieved directional control of the gas flow by using linkage paths established by hydrofracturing and/or by reverse combustion. The cavities were then operated at the lowest possible pressure to minimise gas leakage through cracks which formed in the roof.

Most of the Russian work was conducted in shallow marginal seams, often only 0.6 to 2.1 m thick. This may have contributed to the reportedly poor gas quality and high gas losses. It appears that many of the innovations cited in the Russian UCG literature may not have been translated into operational experience. In addition, during the 1980s, information about UCG technologies virtually disappeared from Russian literature for reasons which are not well understood. The decline in UCG gas production generally coincided with the discovery and development of the USSRs natural gas reserves. This may have simply made UCG locally uneconomic, but it is also possible that the technology was not working well enough. There is some evidence that the Soviets ignored recommendations from their own technical experts, and made minimal use of diagnostics and modelling (Burton and others, 2006). However, the project in Angren (Uzbekistan) was revived in the mid-1980s, and is still running.

At Podmoskovnaya, in the southern part of the Moscow basin, syngas was produced for the nearby Tula power station from 1946 to 1963. The lignite seam used initially was only 34 to 60 m deep, roughly horizontal, and with a thickness varying from 1 to 5 m. It lay in an area regarded as unsuitable for conventional open pit extraction because there was too much water both in the seam itself, and in surrounding strata. When some 2 Mt of coal had been used it was decided to move the operation to a second panel some 5 km away to extend the operating life of the station.

The gasification technique used was to drill a rectangular pattern of boreholes. A generator panel was composed of rows of 8 to 10 vertical wells 25 m apart. The rows themselves were also separated by 25 m. In horizontal seams the flame front undercuts the coal which then drops into the void to form rubble.

Counter current (reverse) combustion linking was preceded by air injection for 3 to 4 days at about 0.3 MPa pressure (3 atmospheres). Air was injected into each hole to be linked and flowed through the porous coal, driving out water. When the air reached the exhaust/production hole, the seam was ignited by dropping incandescent coke down the hole to start the process off. Ignition of the lignite was relatively easy, and initially the production hole was used. After 24 to 48 hours the role of the holes was reversed (Olness, 1981).

Gasification proceeded across the entire width of the panel and progressively along its length, in a stepwise fashion. When a new generator panel was opened, the holes in the first row were linked to each other. Then the holes in the second row were linked, one by one, to the holes in the first row. When the fireface reached the second row of holes the air flow was increased and forward gasification carried out between the second row and the first row (which are now the exhaust/production wells). During this period the third row of holes is linked to the second so that when the coal between the first two rows is depleted, the process can continue by injecting at the third row and exhausting at the second (see Figure 16). The progress of the gasification appears to have been followed and monitored by observing the surface subsidence.

The figure shows a typical plan view of the Soviet process for horizontal or gently dipping seams. The dotted lines are meant to show the linkage channels formed in the coal by a countercurrent combustion step in preparation for gasification (ie using reverse combustion). During the syngas production/gasification stage the gas flows are concurrent. The terms concurrent and countercurrent refer to the direction of the flame front propagation which is either in the same direction as the gas flow (concurrrent), or in the opposite direction (countercurrent).

In the diagram the air inlet manifold is into row 2, and as syngas production declines the product gas manifold will be closed so that the air and flame front will establish links to row 3. As soon as this is

Underground coal gasification 51 69m

23m 23m 23m syngas manifold

row 1

25m gasification cavity row 2

air inlet manifold linking row 3

row 4 drilling and preparing

row 5

boreholes

Figure 16 The linkage between holes at Podmoskovnaya (Gregg and others, 1976)

done row 3 will become the route for the air feed, and, again, as syngas production declines, links will be established to row 4 which will provide the oxidant feed into the reactor area. This will continue until blockages and an increasing pressure drop made the arrangement unusable. Variations in the selection of injection and production holes within the ‘grid’ can be used to adapt to changes in the underground gasifier void which can be caused by roof collapse (possibly causing a blockage) or by changes in reaction rates in different parts of the block. The method leads to the formation of quite wide cavities with somewhat unpredictable cross-linkages and gas flows.

The same basic method has also been applied at Angren where the seam is up to 250 m deep and 24 m thick – and where the boiler(s) have remained in operation. The grid spacing at some of the other stations was later increased to 35 m.

There was a considerable amount of experimentation at different sites, since almost everything had to be proved on an empirical basis. For example, preheating of the injection air by passing it through a burned- out area increased the heating value of the syngas produced and increased the amount of coal recovered. Tests were also carried out using oxygen-enriched air, and a steam-oxygen-air mixture. These are all

52 IEA Clean Coal Centre discussed by Olness (1981). One of the issues which arises during the use of this method is the effect of subsidence on the integrity of the seals around the wells. If the seals are not secure, then there is the risk of providing new pathways for either water flows between different strata or for gas leakage. At an appropriate stage in the operating sequence when they are no longer needed, the wells will need to be plugged, but the literature does not seem to describe this process with any clarity.

Electrolinking experiments were also undertaken. The method offered the possibility of reduced cost, quicker completion and reduced air usage. However, the coal was partially coked in the passages formed, and it was more difficult, sometimes, to know whether the link had been formed. In the late 1950s hydraulic fracturing was tried. This was tried out with an initial pressure of about 0.5 MPa, which was subsequently increased to 1.5 MPa to achieve fracture. While this achieved the link in a matter of minutes, the disruption of the surrounding strata resulted in greatly increased gas losses.

In discussing the Soviet results, Stephens and others (1985) compare the methods used for assessing the gas losses with those in the USA. The Soviets reported 25% losses at Schatska, but only 16–17% at Angren and Yuzhno-Abinsk. They assume that the composition of the gas lost is 50% that of the outlet gas and 50% air, but with oxygen replaced by CO2. The common US practice is to assume that the gas lost has the same composition as the produced gas.

Gas losses computed by the US method are always considerably larger than those computed by the Soviets. For example, the average loss at Angren from 1962-77 was estimated by the Soviets as being 15.8%. Some Belgian visitors who acquired some of the raw data and carried out a nitrogen balance calculated that the loss was more like 25%.

The Soviet work included mathematical modelling of the gasification process, and for the interaction of gaseous products with groundwater. Other research assessed the effects of UCG on the immediate strata. Current work in countries for the FSU is discussed in Chapter 5, including Kazakhstan, Section 5.9, and Russia, Section 5.12. The Angren project is discussed in Section 5.1.1 since Linc Energy in Australia has bought a controlling stake in the company running the site.

4.2 In Europe

Work was undertaken in a number of European countries between the late1940s and the 1980s. There is still active interest in both Poland and the UK which is discussed in Chapter 5 and in Ireland, Slovakia and Slovenia. This section looks at the lessons learned during various trials in Belgium, France, Spain and the UK. A principal interest has been in recovering energy from deep seams, and from higher rank coals but a great deal of work remains to be done before this will be a practical or commercial possibility. The Spanish trial in the 1990s was unusual in that it was carried out in a subbituminous coal which was not a typical European coal. A summary of the European trials is presented in Table 3.

Belgium The Belgian experiment of 1948 at Bois la Dame was an attempt to gasify a semi-anthracite. It seems to have been in a steeply inclined seam with the flame front advancing sideways from an inclined drift rather than upwards from a horizontal one as was more usual (Thompson and others, 1976).

Later, an UCG experiment in a deep seam was carried out in the 1980s at Thulin as part of a joint Belgian-German project. This was in a seam at 860–870 m deep with a number of layers and a total

Table 3 Summary of experience with UCG in Europe (Beath and others, 2004; Burton and others, 2006)

Seam Seam Syngas CV, Test Year Coal type Technique Oxidant thickness, m depth, m MJ/m3 Bois-la-Dame 1948 anthracite SDB 1 air n/a (Belgium) Newman 1949-59 subbituminous 1 75 air 2.6 Spinney (UK) Bruay-en-Artois 1981 anthracite VWs 1.2 1200 air n/a (France) semi- Thulin (Belgium) 1982-84 VWs 6 860 air n/a anthracite Haute-Deule 1985-86 anthracite VWs 2 880 air n/a (France) semi- 3.3–11.1 (with Thulin (Belgium) 1986-87 CRIP 6 860 air anthracite several tests)

Underground coal gasification 53 thickness of ~6 m. The coal was also a semi-anthracite (or a low volatile steam coal in the British classification), non-swelling with a volatiles content of 13.5%.

Four vertical wells were arranged in a star pattern about 35 m from the central well. The permeability of the coal was low. The initial aim of the project was to make a link between two vertical wells using reverse combustion. The tests showed that the reverse combustion technique is not sufficiently reliable to create links with low resistance to flow between boreholes at great depth under the conditions encountered. After two years of unsuccessful attempts (1982-84), it was decided to attempt to connect the vertical holes by deviated drillings.

An underground reactor was prepared by drilling two deviated holes from the existing wells. One was a small-radius deviated hole drilled from the injection well and extended as a horizontal in-seam hole 75 m long. The second was a sidetrack from the production well which crossed the extremity of the in-seam hole. This approach was successful, and gasification took place for about 200 days in 1986-87.

The gasification was terminated because of the formation of a gas bypass. The mass balance on the period showed that 157 t of coal had been completely converted and 183 t of semi-coke was left in the reactor.

Post-burn drillings were undertaken to try to investigate what had happened in the various strata around the gasification chamber. However, most of the data necessary for chemical reactor engineering analysis were not available. Some macroscopic modelling of the gasifier based on thermodynamic equilibria was carried out (Dufaux and others, 1990; Chandelle and others, 1989).

UK Experimental work on UCG started at Newman Spinney in Derbyshire in 1949. Shortly afterwards a second site at Bayton in Worcestershire was commissioned. These provided the opportunity for developing various skills which would be needed to make UCG a working reality. The initial UK programme ran from 1949 to 1959.

The Newman Spinney test was adjacent to an opencast site, and a hole was drilled from an exposed face, through the coal seam for a length of 15 m. Vertical holes were drilled from the ground above the seam to intersect with the in-seam hole, and some 180 t of coal was successfully gasified.

The first technique involved vertically drilled wells that were linked in the coal seam by either forcing high-pressure air between the wells or electrically charring the coal between the wells. The air pressurisation method was only partially successful with only 20 of the 34 links attempted during the test programme operating correctly. When linking was successful, the gasification process was generally also successful, but the product gas quality was fairly poor with average heating value of only 2.6 MJ/m3. The electrical charring linking method was unpredictable and was never completely successful.

The second technique involved drilling in-seam holes, either from an exposed face of the seam at the adjacent open cut mine or from underground tunnels. Given the drilling technology of the time, the in- seam drilling was quite successful and distances of 60–90 m of in-seam hole were commonly drilled. The typical design for this type of gasification test was for several in-seam drilled holes to link two parallel tunnels, for injection and production duty, that were constructed by accessing the coal seam using vertical shafts. These tests also yielded a product gas with average calorific value of only 2.6 MJ/m3.

A third technique was tested using a single in-seam drilled hole. An air pipe was inserted into the hole to serve as the injection well and the product gas flowed around the outside of this air pipe using the same hole. This system gave better results, with the best tests resulting in product gas with a heating value of between 3.2 and 3.7 MJ/m3 over a long period of operation. The only significant issue was that the air pipe sometimes failed due to exposure to high temperatures during gasification.

The research programme was modified in 1956 to focus on the proving of commercial-scale UCG development, with the objective of supplying a small power generation unit of approximately 4–5 MWe output in 1959. The design expected to be used for this scale of development was a multiple borehole arrangement where boreholes, spaced approximately 6 m apart and 100 m long, would link two parallel tunnels that would be used for gas injection and production. Each of the boreholes would operate as an independent gasifier with the product gases combined in the production tunnel. Initial trials of this technology proved to be less successful than expected and construction of the power plant was delayed and then abandoned.

At Bayton various methods were tried out. The hydrofracturing (air pressurisation) method used by the Russians in their brown coal did not work for establishing the linkage bewteen holes in the Bayton bituminous seams.

The UCG programme ended in 1959, with the best experimental results of the study occurring just prior

54 IEA Clean Coal Centre to the end of the research (Beath, 2004). It was reviewed by the National Coal Board in 1976 in the light of the international oil crisis (Thompson and others, 1976). Changes and advances in technology that had occurred since the trials in the 1950s were considered, and this review probably contributed to the decision by the UK government to support the EC UCG research programme in the 1990s, culminating in the El Tremedal test in Spain.

A new research and development programme was started in 1999, with the aim of setting up a further UCG test/demonstration in the UK, which is discussed in Chapter 5.

France A programme of test work was carried out from 1979 to 1985, including in situ trials with parallel laboratory work and theoretical studies. The first tests were carried out at Bruay-en-Artois in the northern coalfield. Various techniques were tried out to assess hydrofracturing behaviour, ignition characteristics and reverse combustion: G boreholes 65 m apart were drilled from old workings 170 m deep down to a lower coal seam which was 1100 m deep. A pre-linkage was obtained by injecting water into the strata over a period of several months in order to modify the existing stresses. Then injection took place under a pressure of ~50 MPa at a high flow rate in order to link the wells. Sand was added at the end of the operation to ensure that the fractures remained open. Gasification was started using an electric ignitor, and the reverse combustion began. The operation was stopped after two weeks because of the self-ignition of the coal at the base of the injection well; G a second test was limited to three weeks operation because of difficulties in maintaining the mine galleries from which the experiments were taking place.

Experiments were undertaken to study the electro-linkage process at Echaux near St Etienne in the centre of France. These were carried out in a seam which was 30 m deep. In the first experiment the electrodes were destroyed in less than 24 hours due to temperatures of ~1500ºC. However the power input of 1.9 MWe produced carbonisation between the electrodes which reduced the electrical resistance between them. The experiment was later repeated with a cooling system for the electrodes, leading to a reduction in the power needed for the production of a coke channel.

In a third series of tests at Haute-Deule in the northern coalfield, the wells were drilled from the surface to a seam 880 m deep. Preliminary injection of water at low flow rate and low pressure was carried out for about three months, and then hydraulic fracturing was achieved using nitrogen foam injection. Tests showed a better linkage was achieved than at Bruay. Ignition, reverse combustion and gasification tests were carried out. There were corrosion problems with the electrical igniters, but reverse combustion took place in October/November 1984 with the injection of a N2, O2, CO2, C3H8 mixture. The production well became blocked by the formation of tars, oxidation products and coal particles.

Spain The trial at El Tremedal was initiated in 1989 and finally abandoned in 1998 (Creedy and others, 2001). Its aim was to demonstrate the technical feasibility of carrying out UCG at intermediate depths between 500 m and 700 m. Three boreholes established the characteristics of the target seam. This was 2 m to 5 m

sparge water tubing coiled tubing low flow tubing

surface casing surface casing

intermediate casing (optional) high flow tubing

process casing injection head / burner process casing

liner

coal seam in-seam liner injection tubing coal seam

Figure 17 The basis of the linear CRIP method. A schematic of an in-seam injection well and of a production well (Sury and others, 2004a)

Underground coal gasification 55 thick, dipping at 30º at a depth of some 530–580 m. The coal is high sulphur (7.6%) subbituminous with 22% moisture, 27.5% volatiles and 14% ash. Its higher heating value is 18 MJ/kg. A second coal seam lies some 7 m to 14 m below the target seam.

Above the seam there was a layer consisting of sand and clay, which allowed water to migrate into the seam, and through which some 17% of the product gas escaped into the strata. A low permeability limestone layer lay below the coal seams.

At El Tremedal the linkage between the injection and production wells was achieved by using oilfield deviated (directional) drilling techniques. The production well was drilled to within 1 m of the injection well. Provided the holes are sufficiently close together, the connection can be achieved by using high pressure nitrogen. If that is unsuccessful, then either high pressure water or reverse combustion initiated from the production well might be used. At El Tremedal the link was easily established.

Using the linear CRIP technique the location of the reaction chamber can be progressively moved. Details of the CRIP and one method of moving it are shown in Figure 17. The version used in the Spanish trial employed coiled tubing to transport the gasification agents (oxygen and water) and to position the injection head inside the pressurised in-seam well. The tubing is fully retractable onto a drum at the surface, and the coiled tubing equipment, which is commonly used in the oil and gas

injection well production well injection well production well injection well production well

clayey sand

coal seam 2.5m

limestone cavity accumulation water influx of rubble a) Start of the gasification b) After 2–3 days c) After 5 days

injection well

production well over burden rock

coal seam

Figure 18 The Spanish linear CRIP test, and the way the cavities develop (Beath and Davis, 2006)

56 IEA Clean Coal Centre industry, was supplied with a wellhead injection assembly, pressure seals and a manifold for connecting the injection gas mixtures to the tubing (DTI, 2004). The well was cased, and there was an in-seam liner which burned when the burner was ignited. The burner was moved from time to time to burn away a new section of liner and create a new cavity.

Ignition of the gasifier was started 4 m from the end of the production well by the introduction of a pyrophoric compound, TEB, to ignite a methane burner located at the end of the coiled tubing. Once the liner was burned through to expose the coal surface, the gasification agents were introduced.

The product syngas was generated as the coal surrounding the ignition point was gasified, creating a caved zone which post-burn investigations indicated extended horizontally to at least five times the seam thickness. Over a period of days, as the consumption of coal creates a cavity, the gasification rate/efficiency declined, and the ignition point was retracted so that fresh coal was accessed. During the trial the coiled tubing was retracted seven times and three ignitions made – however, deviation of the in- seam borehole meant that only parts of its length were in the coal. This limited the locations for possible ignition.

The tests took place during July and October 1997, and involved one run lasting nine days, and another lasting four days. The experiments were terminated when there was an explosion during attempts to ignite the gasification channel for a third time. This was because there had been a build-up of methane after the pilot flame had self-extinguished. The absence of the flame was not detected because the thermocouple at the ignitor had been damaged during the previous ignition. The progress of the first test is illustrated in Figure 18.

The dry product gas consisted roughly of 40% CO2, 12% CO, 25% H2, 13% CH4 and 8% H2S. It contained as much as 50% of water by volume because there was a breached aquifer resulting in water flowing towards the production well. The syngas product was flared.

The test established the potential viability of in-seam drilling and of the use of the CRIP, but there were a number of negative aspects, including problems with water inflow and that the tests only lasted a very short time. A reverse combustion facility was installed, but was not needed, and may not have worked. Reverse combustion and hydrofracturing were used in the largely unsuccessful trials in both France and Belgium.

4.3 In the USA

While a small test had been carried out at Gorgas, Alabama, in the late 1940s, the main programme consisting of more than thirty tests were carried out between 1973 and 1989. Most were part of the US DOE’s development programme, although some were commercially or part-commercially funded. The trials were designed to address specific engineering concerns such as improving the permeability of the coal, and facilitating the linkage between the injection and production wells. The tests investigated the effects of using oxygen and steam compared with air as the oxidant, for improving the syngas yield and quality. They also looked at the procedures to be followed when the gasifier chamber is shut down. The CRIP approach (described in Section 3.2.3) was developed and trialled at Centralia, Washington State and at Rocky Mountain 1 in Wyoming. Most of the tests were carried out in the abundant subbituminous coals in Wyoming, but there were other trials in Texas, West Virginia and in Washington state. Most were carried out in relatively shallow seams, see Table 4.

In addition to the government funded programme, there were several other tests led by private industry (Davis, 2009). These took place mainly in the late 1970s and included: G Rockdale (1978-80) where Texas A&M University led a corporate consortium. The UCG test programme carried out field tests on a Texas lignite near College Station and Rockdale with an emphasis on assessing environmental impacts; G Rocky Hill (1977-80) where the Atlantic Richfield Co carried out a demonstration programme in the Powder River Basin utilising the LVW configuration; G Tennessee Colony (1978-79) where a Texas Utilities demonstration was carried out with a licence using Russian LVW technology in Texas lignite. It was abandoned because the economics did not look attractive.

The US DOE programme The US DOE programme consisted of a well planned series of in situ trials which were intended to explore the performance and behaviour of UCG reactors. There were six field test programmes at: G Hanna, WY, run by the Laramie Energy Technology Center; G Hoe Creek, WY, run by the LLL; G Pricetown, WV, run by the Morgantown Energy Technology Center in West Virginia; G Centralia, Washington state, run by the LLL; G Rawlins, WY, in a steeply dipping seam run by the US DOE and Gulf Oil; G Rocky Mountain 1 which took place very close to the Hanna site, and was run by an industrial

Underground coal gasification 57 Table 4 Outline details of the principal trials in the USA (Davis, 2009)

Programmes which were government funded

Seam Date Organisers Location Configuration Coal rank Seam depth, m thickness, m

1971-81 Laramie ETC Hanna, WY LVW-RCL subbituminous 7 80

Lawrence 1972-82 Hoe Creek, WY LVW-RCL subbituminous 5 30 Livermore LVW with drilled 1977-80 Morgantown Pricetown, WV bituminous 3 300 link

1976-82 Gulf Oil/DOE Rawlins, WY SDB subbituminous 7 120–200

Lawrence 1981-85 Centralia, WA CRIP subbituminous 6–8 20–50 Livermore Rocky Mountain 1 1986-93 IC/DOE LVW-CRIP subbituminous 7 75 (Hanna)

Programmes led by private industry

Date Organisation Location Configuration Coal rank

near College Station 1978-80 Texas A&M university LVW-RCL lignite and Rockdale, TX

1976-80 Texas Utilities Tennessee Colony, TX LVW lignite

1977-82 Atlantic Richfield Co Rocky Hill, WY LVW-RCL subbituminous

ETC Energy Technology Center (at Hanna, WY) IC Industrial Consortium, led by the Gas Research Institute LVW linked vertical wells RCL reverse combustion linkage SDB steeply dipping bed

consortium led by the Gas Research Institute. Its purpose was to support a comparison of the use of LVWs and a horizontal CRIP, with industry providing a 50% cost share.

All the tests were intended to address specific aspects of engineering and practical concern. The programme had the enormous advantage that it was well documented, and the results were all available in the public domain, although now, 20–30 years later, some of the original material is no longer available. Davis (2009) comments that most of the currently available information is from second, third and even fourth hand publications; usually by authors that were not a part of the original project team. This is a common problem with recovery of technical information that has passed through several hands as it can become distorted and biased. Similar comments would apply to the information about the tests carried out over many years in the USSR with additional problems associated with translations which may have been undertaken by non-technical personnel.

First series (Hanna I-IV) The first in situ UCG project in Wyoming was located in the Hanna Basin two miles south of the town of Hanna. The coal is low-sulphur and subbituminous and the seam used was some 80 m deep.

The tests were performed to evaluate and optimise the methods that were then in use in the USSR (Beath and Su, 2003). All were air-blown. The Hanna series focused on the LVW configuration with RCLs to establish high permeability communications between process wells. Initially these were 20 m apart, while in the last trial greater distances were used.

Hanna II had a highly instrumented array of thermocouple wells that were used to assess the development of the RCLs between wells. The tests provided detailed information in the seam being gasified on the development of RCLs between wells and of the growth patterns during forward gasification operations. Two patterns were established: G one was the tendency for the reactor to grow to the roof of the coal seam; G the other was for the reactor to develop along the centre line between injection and production wells in a tear-drop shape with its apex around the production well (see Figure 6b).

58 IEA Clean Coal Centre Data from Hanna II demonstrated that RCL produced multiple channels during the linking by reverse combustion with only one being completed. Once linking was established and forward gasification initiated, the reactor grew upward and along the centerline between the point of injection of the combustion gas and the removal of the product gas at the base of the production well taking a teardrop shape. This was the case no matter what the path of the completed link.

These tests provided the technical data that created the major private industry interest in UCG as a potential source of fuel/synthesis gas.

Hanna III was designed to collect environmental data. Hanna IV operated with wells which were considerably further apart with well spacing of >30 m, which resulted in significant problems in developing the RCLs (Davis, 2009) because of the presence of chevron fractures perpendicular to the centre line of the chamber.

Second series (Hoe Creek I-III) The second series of tests was conducted by the LLNL (then the Lawrence Livermore Laboratory) for the US DOE at a facility known as Hoe Creek which was some 25 miles south of Gillette, Wyoming. These aimed at developing new and better techniques for linking the wells than those being used at Hanna. The experiments were conducted in a seam 30–40 m deep and some 5 m thick (Burton and others, 2006). The programme ran between 1976 and 1979, and tested three different linking methods: G explosive fracture; G reverse combustion; G directional drilling (with combustion initially at the base of the injection well).

Hoe Creek was a site that was too shallow for controlled and successful UCG, with an extremely weak roof causing subsidence reaching the surface. However, the knowledge gained there demonstrated the need for a positive linking mechanism such as directional drilled boreholes between the process wells.

Hoe Creek turned out to be a less amenable site for the LVWs process than Hanna. There were problems with maintaining the process reactions along the centre line between process wells. When the injection well casing burned to the top of the seam, the reactor actually moved up into an overlying seam when the weak roof failed.

In Hoe Creek I explosive fracturing was used, and the test continued for 11 days with air injection. Approximately 7% of the gas was lost into the rock formation.

Hoe Creek II used reverse combustion, and gasification lasted for 43 days. Water influx significantly lowered the gas quality. To decrease the water inflow the operating pressure in the burn zone was increased. This resulted in a significant amount of gas (approximately 20%) being lost into the rock formation. Much of this loss is thought to have occurred when the burn zone collapsed, exposing the upper Felix No 1 seam, which was at a lower hydrostatic pressure. It was this event which happened in a strata which would now be classed as having high environmental risk (and would therefore not be considered for development of any kind), which gave UCG an unjustified reputation as a serious potential hazard.

Hoe Creek III combined a horizontally drilled link between two vertical wells with reverse combustion. As in Hoe Creek II, the burn zone moved into the upper coal seam, and this resulted in a gas loss of approximately 17% during the test. Subsidence eventually propagated to the surface at the Hoe Creek II and III Sites.

The gasification processes introduced toxic volatile and semi-volatile organic compounds into the aquifers at the Hoe Creek site, especially when the burn zone was over-pressurised to help mitigate water influx. But the persistent groundwater quality problems are the result of migration of contaminants derived from the nonaqueous phase liquids that are gasification by-product residues formed by the pyrolytic breakdown of the coal (for example, viscous tars, semi-volatile and volatile organic compounds). The problems were exacerbated by subsidence and collapse of the cavity roof, which resulted in the interconnection of the hydrostratigraphic zones and contamination of all three local aquifers (Burton and others, 2006).

The tests at Hoe Creek provided the basis for a number of developments which included the proof-of- concept validation of the CRIP configuration at Centralia, described below, the validation of subsidence models, and the first oxygen/steam injection experiments in the USA. A wide range of instruments and monitoring tools were used, including the use of tracers. The tests also gave rise to the first recognition of possible groundwater hazards which are discussed further in Chapter 5.

Third series at Pricetown The Pricetown test in West Virginia was the only one in a bituminous (agglomerating) coal seam some 270 m deep. It was heavily instrumented. The module used a directionally drilled horizontal borehole as the link between the injection and production wells. Vertical wells were drilled to intersect with the

Underground coal gasification 59 borehole at a spacing of about 20 m. After ignition, the Table 5 Rawlins US DOE test results (Singleton gasifier was operated in a forward combustion mode for and Pilcher, 2007) some 8–10 days, until oxygen was detected in the product gas. When the flow was reversed, the function of the Test 1 Test 2 wells reversed, and good gas quality was obtained for few more days. The agglomerating property of the coal air blown steam/oxygen apparently sealed the walls of the gasifier limiting the → primary gasification reaction, (2C+O2 2CO). The test 30 days 65 days clearly demonstrated the impact of coal agglomeration on 27–54 t coal/d gasified 90–180 t coal/day gasified the gasification process (Davis, 2009).

syngas 12–14.8 MJ/m3 Fourth series at Rawlins syngas 4–5.5 MJ/m3 5/1 coal/oxygen ratio (by weight) The fourth series of tests at Rawlins in Wyoming between 1979 and 1981 was carried out in a steeply dipping seam of subbituminous coal. This was thought to have been the most successful of the Russian UCG configurations, although the Russian work was in bituminous coals.

Two tests were carried out in a coal with a seam dip of 60º, one using air and the other with oxygen. Full environmental compliance was reported along with a thermal efficiency of more than 80% (Beath and Davis, 2006). The test conditions are shown in Table 5. It was reported that good control of the process was maintained, and a turndown ratio of 5:1 achieved. Compared with UCG in horizontal strata, a higher thermal efficiency was achieved, and a lower oxygen demand (Singleton and Pilcher, 2007).

The Rawlins 2 test was controlled with the intent of making a high quality syngas, and was succesful in obtaining the required H2:CO ratio. The was the basis for the UCG to ammonia project proposal, a winner in Round One of the Clean Coal Technology programme in 1987, although the plant was never built.

Fifth series at Centralia (Widco mine, Tono basin) As a result of the results coming from earlier trials, the LLL initiated a study of the development of the reactor between process wells. This included laboratory studies of large blocks of coal to determine the pattern of reactor development between vertical boreholes.

The programme was extended to an outcrop of a coal at the Widco mine, Centralia, WA to experiment in an actual coal seam (see Figure 19). A series of five tests were carried out in the coal seam with different well configurations. They took place in adjacent sections of an exposed coal face such that the site layout

incinerator

produced gas

product gas well

oxygen/ steam injection observation well

coal seam reaction zone

Figure 19 Schematic view of the large block experimental configuration (Burton and others, 2006)

60 IEA Clean Coal Centre allowed both ease of access and extensive monitoring mostly in the form of thermocouples in well pits.

The coal was subbituminous with 14% ash. The tests included a series of trials known as the large block experiments which took place in 1981-82. These were of relatively short duration, taking about four days each. They were followed by two more tests in 1984-85, with a partial seam CRIP trial and a full seam CRIP burn. These tests used the linear CRIP arrangement, and there was a 30-day test to demonstrate the operation of a burner to melt through the injection well liner so as to establish a new injection point for the oxidant, which is the basis of the CRIP. Silane gas (SiO4) was used with propane to ignite the burns and to melt the horizontal casing, to control the movement of the burn cavity (Burton and others, 2006). Experiments were run with different steam/oxygen injection ratios and flow rates.

The site was quarried about a year later and the small reactor chambers examined, so that aspects of the simulators/models used to calculate cavity shapes could be directly validated. This allowed the investigators to improve their understanding of how the burn cavity grows and is influenced by site geology. They showed that: G the cavity develops upward with a V-shaped pattern; G there is virtually no growth downward; G the path between the injection and production point is defined by the well location (Davis, 2009).

Sixth series (Rocky Mountain) The name Rocky Mountain was adopted to distinguish these trials, as the site is very close to Hanna where the first series of tests took place and in an almost exactly similar formation in a horizontal subbituminous coal seam. A steam/oxygen mix was used. In the two tests, a comparison was obtained between: G the use of linked vertical wells (LVWs) using the Soviet method; G the CRIP using the parallel in-seam boreholes method where the two process wells are both in- seam, and intercepted at an angle of about 14°. The process then progressively gasified the coal lying between the two wells (see Figure 6e).

In the LVWs, it took 65 days to burn out, and some 60–90 t/d of coal were gasified producing a syngas with a heating value of around 8 MJ/m3. In the CRIP test, 90 days of operation were achieved in four reactors, and some 60–180 t/d of coal was gasified with a heating value of 9–10 MJ/m3 (Beath and Davis, 2006). The CRIP manoeuvre was successfully performed three times during the programme as planned.

During this test, the movable igniter/burner was moved to melt a stainless steel liner in the injection well. Melting the liner relocated the oxidant injection point away from the previous cavity into fresh coal and when the product gas quality declined the injection point was moved.

The sequence in the CRIP operation was as follows: G the igniter system was flushed with N2 for a few minutes at a pressure 0.14 MPa above downhole pressure;; G air injection flow rates were established to the well casing to create a system backpressure; G with the igniter isolated, the low pressure sliane bottle was filled to a pressure required to deliver 1.5 tube volumes of silane at downhole pressure; G the silane was injected to the well and the igniter tip thermocouples closely monitored; G methane was then supplied by slowly opening the supply; G when the CH4 reached the end of the igniter tubing an increase in the thermocouple readings was seen, and the CH4 flow increased; G methane gas flow was maintained until the thermocouples became very hot and the product gas analysis indicated good combustion with no residual O2; G for each CRIP manoeuvre, the remote torch/burner was positioned at the desired location G an air flow was established, and steam flow gradually eliminated; G silane was delivered downhole through the igniter tube; G methane flowrate was slowly increased; G usually within ten minutes of increase, liner thermocouple and Time Domain Reflectometer (TDR) cable failures indicate burnthrough of the liner (for more information about TDRs see Granite Island, 2009); G methane flow is gradually decreased and the coiled igniter tube flushed with N2 and retracted at least 20 m upstream; G with the igniter safely retracted the air flow is slowly increased over about 10 hours with a transition to steam/oxygen; G stable steam/oxygen rates are established and gradually ramped up to required values (1275 sm3/h of oxygen and 2550 sm3/h of steam) during the next 48 hours.

Carbon County trial Williams Energy conducted a UCG pilot project in Carbon County, with a view to possible commercialisation. Field tests in steeply dipping coal seams in the Indian Springs Coal Resource area near Rawlins, WY were conducted in April and August 1995. The test was located adjacent to the site of

Underground coal gasification 61 the Rawlins UCG trials carried out by the Gulf Research and Development Co in the late 1970s. It was conducted in the same coal seam, but at deeper levels. The coal seam is approximately 18 m thick with a dip of 55–60°. The purpose of the test was to corroborate earlier studies that demonstrated the feasibility of using UCG in steeply dipping coal beds. The test was unsuccessful and resulted in groundwater contamination due to poor well linkage and operation of the UCG reactor above hydrostatic pressures (GasTech, 2007b). It appears that there were problems in drilling both the injection and production wells due to the disturbed geology. Difficulties were encountered when trying to establish the link between the wells and high pressures were applied while seam ignition was being attempted. Monitoring before and after operations indicated that some organic compounds increased in concentration in groundwater after the burn. Post test efforts including fracturing the formation, caused further spread of the contaminants (Davis, 2009). As at Hoe Creek, high benzene levels were measured in groundwater aquifers within the target coal and in overlying and underlying sandstone units (Burton and others, 2006).

4.4 In China

It is estimated that there are nearly 300 abandoned mines with some 30 Gt of coal resource (Liang and others, 1999). Chinese tests and trials (before 2007) have been almost entirely based around the use of conventional mining roadways and access and developing ways of extracting more energy from a deposit using UCG. This means that most of the gasifiers operate at low pressures to limit gas leakage through the stoppings and seals, and through mining induced fractures in the seam or in the surrounding rock (Creedy and others, 2004). Undersurface gasifiers were described in Section 3.2.5.

The earliest tests were carried out in the late 1950s and during the 1960s, but combustible gas was only obtained for relatively short periods. However, since the mid-1980s, UCG testing has been encouraged in China’s national development plans in order to make the fullest use of the coal resource. In 1991, the State Science Commission published medium and long-term objectives to 2020 which called for the completion of research and testing, and the introduction of commercial UCG projects in China.

The aim of much of the work has been to recover remnant coal from exhausted mines prior to abandonment. The identified resource for UCG in terms of unworked coal and pillars is said to be some 30 Gt. The overall resource in China is said to be around 1 Tt, vastly greater than the proved recoverable reserves, which are commonly quoted as being around 115 Gt (Creedy and others, 2004; BP, 2007). More than half of the resource lies at a depth of below 1000 m, so in the long term, China is likely to have a considerable interest in deep seam UCG.

Most of the UCG trials have used air blown systems to produce low quality gas, with varying degrees of success. Control is limited to increasing, decreasing, pulsing or reversing the airflow, and a stable gas quality can be difficult to maintain by remote control (Creedy and others, 2004).

oxidant

syngas

bore hole

pyrolysis reduction oxidation

tunnels ash tunnel

coal seam

original tunnels

Figure 20 Long tunnel large section in-seam gasification layout (Liang and Shimada, 2008)

62 IEA Clean Coal Centre Tests were carried out on the long tunnel large section arrangement (see Figure 20) in 1994 and 1996 at the Xinhe mine, Xuzhou and the Liuzhang mine, Tangshan. This method was shown to be capable of producing a gas with heating values in the range 12 to 14 MJ/m3 and a hydrogen content of up to 50%. The long gasification tunnel (>200 m) facilitates heat transfer to the coal seam and ensures that there is enough coal in the reactor to maintain process stability. When using air as the oxidant the syngas heating value is nearer 4 MJ/m3, and the speed with which the gasification face advances ranges from 0.2 to 0.5 m/d (Liang and others, 1999).

The two-stage process involves oxidation using air to heat up the reaction chamber, followed by steam injection. This decomposes to form CO + H2. It can produce a syngas with heat values in the range 3 12–14 MJ/m , and a H2 content of around 50%, but is more difficult to control than the undersurface arrangement (Creedy and others, 2001). However, not all the sites where it has been used have operated as two-stage processes. It is thought that the reaction zone at the face is maintained by periodically reversing the injection and production flows, and that the reaction does not spill around into the injection tunnel because the oxygen is used up before the gases get to the end of the ‘face’.

A number of tests were carried out from 1997 onwards using the long tunnel method, and details are given in Table 6. Most were in quite shallow seams (at <100 m depth). Some of the seams involved were steeply dipping, and all were unmineable by conventional methods. Earlier Chinese work (discussed in Section 4.4) concentrated on recovering more coal from otherwise abandoned mines.

In an overview of the Chinese programme, Li and others (2007) highlighted the work of the UCG research centre since 1984 at the CUMTB. This has included some testing in an experimental laboratory rig. This has tested various parameters including different coals, oxidant flow rates and the flow direction, and the effects of using different mounts of oxygen and steam. Some of the results are reported by Liang and Shimada (2008). Much of the work has been to support the LTLSTS process shown in Figure 20. This technology has been demonstrated at the Liuzhuang, Xuzhou Xinha and Xinwen Suncun mines.

In the two-stage method, steam and air are injected alternately. High temperatures are achieved along the coal ‘face’ during air injection. Steam injection then results in the production of a high heating value gas with 12.5 MJ/m3. The air injection is changed to steam when the oxidation zone temperature is >1000ºC, and it is reversed back to air when the temperature drops to <700ºC. The gasification efficiency is higher for reverse two stage gasification than it is for forward two stage operations (Liang and Shimada, 2008).

Current activities are outlined by Liang and Shimada (2008) and are discussed in Chapter 5. The China University of Mining and Technology in Beijing has established a UCG Research Centre. This has a large experimental apparatus (4.5 x 1.2 x 1.6 m) in which simulations of the underground gasification process can be carried out. In addition the conventional two borehole method of UCG is being trialled.

Table 6 Summary of experience with UCG in China (Beath and others, 2004; Feng Chen, 2008)

Seam Seam Syngas CV Test Year Coal type Technique Dip, ° Oxidant* thickness, m depth, m MJ/m3 MV bit/gas Liuzhang 1997 tunnel 2.5–3.5 100 steam 12.2/12.8 coal

Xinhe 1997 fat coal tunnel nk 80 steam 11.8/14.6

Liuzhang† 2001 MV bit tunnel 2 25 n/a steam 11.5

Suncun 2001 bituminous tunnel 2 80 air 10.8

Xinhe† 2001 fat coal tunnel 3.5 68–75 n/a steam 12.2

Xiyang 2002 anthracite tunnel 4 200 air 4.0–6.2

Xiyang† nk anthracite tunnel 6 22–27 190 steam 11.9

Suncan 2002 bituminous tunnel 2 80 air 8.5

Kiezhuang 2002 bituminous tunnel 2.6 N/a steam 12.2

Feicheng† nk fat coal tunnel 1.3–1.8 5–13 80–100 air 5.1

Xinwen† nk fat coal tunnel 1.8 25 60–75 steam 11.4

* steam is assumed to imply a steam/oxygen mixture † includes data from Feng Chen (2008)

Underground coal gasification 63 4.5 The outcome from the trials

The fact that the trials have taken place over a long period, in differing circumstances, and in differing coals at various depths, means that it is inappropriate to generalise from particular results which should be regarded as largely site and test specific. During the period, other technologies such as seismic exploration, in-seam drilling, and the application of more powerful computers to data analysis, have changed many aspects of the interpretation of the results out of all recognition. There have also been many important changes in environmental sensitivities and requirements during the period.

Since UCG requires an integrated multi-disciplinary approach to the production of syngas involving a wide range of different aspects, all the trials had severe limitations. Virtually all were on a small scale, and none has demonstrated the technology on a commercial scale meeting modern environmental requirements. The total amount of coal gasified, including that in the USSR during fifty years, remains small, at around 15–20 Mt. Many trials took place in relatively shallow seams which would not currently be regarded as a target for commercial development. The operations in shallow seams (less than 100 m deep) limits the pressure that can be used in the reactor and increases the risk of gas leakage.

In a wide ranging review Vasyuchkov and others (1998) discuss unconventional mining technologies for clean and efficient power generation, including UCG. They comment that a number of semi-commercial, demonstration- and pilot-scale UCG projects have been undertaken, justifying renewed interest.

Three main methods of carrying out UCG seem to have emerged for further development, in addition to those for steeply dipping seams (where there are far fewer prospects) and to the Chinese efforts to recover energy using man-made tunnels in abandoned mines.

The three methods are: G the Soviet methodology now embodied in ␧UCG technology using vertical wells and a combination of hydrofracturing and reverse combustion to establish the necessary linkages. This is now being trialled at Majuba in South Africa (see Section 5.11.1) and at Kingaroy, Australia; G a parallel technology which uses vertical wells, but with the linkages established using in-seam boreholes; G CRIP technology, either in an in-seam borehole coupled with vertical wells to remove the syngas formed or using the so-called parallel CRIP technology where two parallel in-seam boreholes are drilled through a seam, and then at the end, turned to meet each other – at a point where a vertical ignition hole can be drilled. This is being trialled at Bloodwood Creek in Australia (see Section 5.1.2).

Many principles have been established as a result of carrying out the tests, for example: G gas losses from shallower seams where much of the work has taken place are generally much higher than those from deeper seams, and it is more difficult to maintain a water seal at the lower pressures; G water contamination is also a more serious possibility in shallower strata which are more likely to carry aquifers with potable water; G the lower rank coals are generally more permeable and reactive than higher rank ones which has implications for the ease with which linkages can be made between wells; G lower rank coals may also be somewhat softer, which could affect the stability of in-seam boreholes; G coal seam depth is a key parameter which affects the pressure at which it is permissible to operate, particularly if it is needed to operate at below the hydrostatic pressure such that water flows into the reactor chamber rather than out of it into adjacent aquifers. The hydrostatic pressure increases at approximately 1 MPa per 100 m depth; G site shut-down procedures have been established, with the cavity being ‘steam cleaned’ and washed at the end of its useful life; G a much higher heating value gas can be obtained using oxygen-enriched air, and commercial considerations will determine the relative economics of air compared with oxygen/steam operations, since different products can be produced.

However, the results are all ultimately site-specific, as with other issues relating to the use of coal, because many factors will be dependent on the precise local geology, the nature of the particular coal deposit and the test conditions. The tests have included coals at varying depth and of different ranks. They have also used different methodologies. While certain principles, methodologies and monitoring techniques have been established, the results have not yet justified the claim that UCG is a ‘commercially proven technology’. That process is currently under way, and hopefully during the next five or ten years the technology will emerge as commercially proven. The current situation is that different parts of the technology have been demonstrated/proved separately but each in unique circumstances (as is commonly the case with emerging coal technologies). Care will still have to be

64 IEA Clean Coal Centre taken before translating success on one site to a project on another, and new prospects will almost certainly need to go through the basic stages of detailed exploration, assessment and a long underground test, before a commercial-scale operation can be planned and costed.

The extensive work in the USSR over a period of around fifty years has been described as ‘commercial’, but a more accurate description would probably be to say that some of the operations were on an industrial scale. They would probably not have been profitable under a current economic model. The objective was simply to produce a low heating value gas for use as an industrial fuel or for power generation without having to send men underground to mine the coal (Barone and Malavasic, 1987). Stephens and others (1985) comment that with the reported gas losses, close well spacings and low gas product quality, an equivalent UCG activity in the USA would produce unfavourable economics. During much of the time when the early work on UCG was taking place, particularly in the USSR, gas leakage into the surrounding strata was regarded as an acceptable ‘hazard’. The Soviet efforts also resulted in widespread groundwater contamination (Liu and others, 2007). The standards that would be set now are much tighter than those applying when much of the work described in this chapter was undertaken.

Most of the operations described in this chapter have not lasted long enough to require the mechanical integrity testing of wells. However, the Soviet experience indicates that the life of an injection well can be in the range of two to four years.

Outcomes Probably the most important result of the UCG work in the USA was the publication of comparative results for UCG tests using the LVWs method and the newly developed CRIP. Information from the US DOE was available in the public domain.

The basics of the CRIP method were discussed in Section 3.2.3. The injection well is drilled in-seam using directional drilling techniques and is lined with an appropriate support material which will burn away. The linear CRIP technique involves the use of a burner attached to coiled tubing see Figures 17 and 18, which shows the arrangement used in the Spanish trial which took place in 1997. Once the injection point is near the production well, the gasification is initiated, and as the cavity develops and becomes exhausted, the CRIP is moved to a new location as illustrated in Figure 14. The borehole lining is burned away en route, and a new cavity is established. This facilitates close control of the gasification location and its progress through a seam. The principle works with either a vertical production well or with a parallel in-seam production well (Shafirovich and others, 2008a).

Some bituminous coals have been successfully gasified underground, but more of these tend to swell when heated (compared with lower rank coals) and this can reduce the permeability of the link between the wells. Using the CRIP technique should largely avoid these problems, albeit at increased cost. Many higher rank coal seams are deeper and thinner than lower rank ones, although around the world there is a great deal of variability and variety. UCG may be particularly useful for high ash content bituminous coals such as those in India and some in Australia, since the ash remains underground.

Deeper seams will more commonly consist of coals of higher rank, where it may be more difficult to establish the necessary linkage between the wells. In these seams, the use of directional drilling may be preferred. In addition, operations in deeper seams require higher injection pressure, but are less likely to interact with potable water aquifers. Operating at a higher pressure can provide benefits in terms of the syngas composition and its heating value. Most of the European trials have looked at seams lying below 500 m.

Much of the gas produced has been from shallow deposits at low pressures and using air-blown systems, and has been mainly in the 4–6 MJ/m3 range. It is possible to produce a syngas with a heat value in the 12–14 MJ/m3 range, and optimisation of all the reaction conditions in a deep UCG prospect might produce a syngas with a heat value of 16 MJ/m3.

Little work has been done in lignites, and almost none in very thick seams, where controlling the location of the underground reactor is likely to be considerably more difficult. The work done in deep seams and in higher rank bituminous coals and in anthracite is also very limited.

While the trials included coals of different rank, the results have been too scattered to draw firm conclusions and all that has been established is that given the right conditions, coals of virtually all ranks can be gasified underground.

Commercial-scale operations which are the objective of the work described in Chapter 5 could have significant implications for groundwater use compared with those from the relatively small-scale trials so far undertaken.

Underground coal gasification 65 5 Prospective developments

There are a wide range of countries and locations where UCG development is being actively considered and assessed. The spread of activities, both current and historical, is illustrated in Figure 21 which is based on data from the LLNL.

In both Australia and South Africa, projects that are aimed at becoming commercial and profitable are already under way, although it will probably be at least another five to seven years before they achieve this objective. Most of the work described in this chapter has been undertaken after 2000, although the planning and setting up at Chinchilla in Queensland, Australia, had started before then. Some of the work in China described in Section 5.4 also took place in the late 1990s, and one current project is projected to expand to commercial scale. The work in Poland (including some earlier work) is discussed in Section 5.5 under the EU HUGE project.

Countries where there are prospective developments but where the assessment is still at an early stage, include: G Indonesia; G Kazakhstan; G Mongolia; G Pakistan; G Vietnam.

The project design and assessment process is rarely well discussed in the literature. However, in Brand (2008) the various steps are discussed, comprising: G the initial site proposal; G a geology and coal quality report; G a rock mechanics report; G a hydrogeology study; G designing the well spacing and panel layout, together with setting up operational procedures; G the drilling design for both vertical and directional holes; G ignition and process control of the panels.

It is described as an iterative process within which all the different factors affecting coal extraction, gasification and the groundwaters are taken into account. It is implied that proceeding to the next stage is dependent on a satisfactory outcome from the previous steps. The paper suggests that there is no such thing as a generic UCG method, and in each of the areas shown, the different parameters would have to

Promgaz Hoe Creek / RM-1 Alberta Angren* Wulanchabu

Centralia

Areas for CO2 storage highly prospective

prospective

non-prospective UCG Arkaringa prior test sites Sasol Majuba UCG pilot operations announced/planned Chinchilla, Bloodwood Creek Kingaroy LLNL led

* Angren has been operating for several decades

Figure 21 Map showing the location of UCG activities, past and present (Friedmann, 2008)

66 IEA Clean Coal Centre be considered and engineered appropriately for effective UCG at a particular site.

It should be noted that surface developments of all kinds, including the building of new power plants, factories, office blocks and even houses are subject to constraints and regulatory barriers (as discussed in Section 6.5). These cover emissions, effluents, noise, visual intrusion and other factors, together with the need for resultant infrastructure developments in the form of roads, power supply and water. In most cases these constraints are reasonably well understood, and can be quantified and the provisions can be costed. An example of an aspect that is more difficult to assess in some circumstances is the change to the local supply/demand for water and its distribution when it rains.

5.1 Australia

In Australia there are a number of companies undertaking trials and/or doing feasibility studies. Coal is a huge resource in Australia, and the country is by far the world’s largest coal exporter. It has substantial resources with thick seams lying broadly from 150 to 400 m deep which could be suitable for exploitation by UCG. The Australian developments, alongside the Majuba project in South Africa, are probably closer to commercialisation than those elsewhere. The two most advanced projects are in the Surat Basin in Queensland, while there are other prospects in Victoria and Western Australia. One company plans a development in South Australia.

A dispute has arisen recently over the exploitation of the coal in Queensland, and its accompanying CBM. The technical basis of the dispute is that Linc Energy ( see Section 5.1.1 below) has been operating its UCG project under the Minerals and Resources Act. Queensland Gas is interested in CBM production and has tenements over some of the same land under the Petroleum and Natural Gas Act. In the short term the Queensland Supreme Court decided to allow pilot trials to continue, pending a longer- term decision about which interests (UCG or CBM) should take precedence (The Australian, 2008). This raises interesting issues relating to the regulatory control of UCG, and to possible competition between the use of CBM from a coal seam and its exploitation for UCG.

5.1.1 Linc Energy In early 2000, Linc Energy carried out an UCG trial in a block of coal 140 m deep in the Surat basin in Queensland. The UCG technology used involved vertical wells and hydraulic fracturing and reverse combustion linkages was used, under a licence from Ergo Exergy (for the ␧UCG technology). Syngas was produced for just over two years from a seam that was more than 8 m thick. More than 35,000 t of coal was gasified using air as the oxidant, producing some 80 Mm3 of gas with a heat content varying from 4.5–5.7 MJ/m3.

The coal used is a top end subbituminous coal with an ash content of 28% and perhaps a little higher. In terms of its quality and distance from an export terminal it is regarded as ‘stranded’ coal with low potential for use in the export market.

The pilot burn involved nine injection/production wells during the period, and there were nineteen monitoring wells to assess any changes in the groundwater. The timeframe for the project was as follows: G November 1997, site selection; G September 1999, design for the pilot burn complete; G December 1999, construction complete for the pilot burn. The first gas was produced and flared; G June 2002, after more than two years operation, the controlled shut-down of the underground pilot reactor was completed.

There was an extensive environmental assessment made following the shut-down, and no deleterious impacts were found. It should be noted, however, that the area of coal involved was quite small, covering an area of only some 30 m by 100 m. As the UCG reactor is operated below the surrounding hydrostatic pressure, in principle, nothing leaves the process other than through the production well. The reactor chamber was surrounded by a number of monitoring wells with sample points and piezometers measuring the hydrostatic head. At the end of the two-year programme, and as part of the shut-down procedure, the reactor was blown through as it cooled down to remove any residual pollutants, using the ‘clean cavern’ approach discussed in Chapter 3.

Since the initial trial there have been changes in the management, and the company is operating independently of the ␧UCG technology and Ergo Exergy, to whom they were previously licensed. In May 2006, Linc Energy became a company listed on the Australian Stock Exchange. Linc Energy have been quite commercially aggressive, commonly mentioning their share value during technical presentations, and they have been successful in raising considerable amounts of capital to fund their projected developments.

The original business plan was to use the syngas for power generation, but in view of the relatively low

Underground coal gasification 67 price for electricity in Queensland, Linc Energy decided to pursue the policy of producing higher value products. This involves a considerably increased technical risk as syngas to liquids (STL) processes are less forgiving of variations in the syngas quality than turbine based power generation. Linc Energy commissioned an external study by PriceWaterhouseCoopers to assess the prospects for UCG, which was published in May 2008, and is available on the Linc website (Linc, 2008b).

During the period after Linc Energy’s public listing, the focus of activities has been to establish the conditions for an air-blown UCG panel to deliver syngas to a syngas-to-liquids (STL) process development unit (PDU). Following extensive assessments, a new coal panel was set up for UCG, and a PDU for the production of Fischer-Tropsch liquids commissioned towards the end of 2008.

The UCG development is based on linking an in-seam borehole with vertical wells, and not on the Russian ␧UCG system. Using this method, the in-seam hole(s) provide the linkage routes between vertical injection and production wells, and hydraulic fracturing will no longer be needed.

The main aim of the trial is to supply air-blown gas of sufficient quality and quantity for the PDU. The syngas has a typical composition (on a nitrogen free basis) of H2 32%; CO 17%; CH4 18% and the H2/CO ratio of 1.88 is ideal for the Linc syngas to liquids process. In ten months some 2000 t of coal has been gasified, representing about 7 t/d. In May 2009 a controlled shut-down of the generator was started. The depressurisation and rehabilitation of UCG reactor cavities at the end of their operational life is a process that will have to be carried out many times during commercial-scale UCG operations, and Linc Energy will use the current experience to refine the cavity cleaning techniques used, to achieve the best possible environmental and operational outcomes (Minotti, 2009).

After initial discussions with different syngas-to-liquids (STL) technology providers and several months of R&D carried out at the University of Kentucky’s Center of Applied Energy Research (CAER) the STL pilot plant was finally designed in South Africa by local engineering companies. At CAER a syngas with a similar composition to that produced from UCG at Chinchilla was used as the feedstock to determine the best catalyst to use (cobalt), as well as the operating temperatures and pressures applicable. The pilot plant is over 70 m long and eight stories high. It includes the facilities for syngas clean-up, compression, two FT fixed tube reactors and basic distillation equipment to separate the different fractions, including diesel. The PDU has the capacity to produce some 5 to10 bbl/d and is intended to establish the practicality of producing liquid fuels from an UCG operation.

Linc Energy currently operates under a Queensland Government Mineral Development Licence. However, in view of the dispute referred to earlier, and the probability that the Queensland government would give priority to CBM as an established technology over UCG which is developing, Linc Energy decided to move its commercial-scale UCG/STL project to South Australia. One potential site is in the Arkaringa basin some 800 km northwest of Adelaide where there are very substantial coal resources, and the basin is said to contain one of the largest contiguous coal deposits in the world (Coober Pedy, 2008). Some of the necessary exploration has already been carried out by Sapex Ltd (Sapex, 2007).

To facilitate the development, Linc Energy acquired Sapex Ltd, giving Linc Energy access to large coal exploration areas in South Australia. The coal is subbituminous with typically 38% moisture, 11% ash and 1% sulphur. The costs involved are not inconsiderable, and Linc has already spent some A$50 million at Chinchilla, while the Sapex takeover involved A$104 million (Syngas Refining, 2008b).

Developments at Arckaringa by Altona Resources were already under way with proposals for a conventional mining operation with an on-site CTL plant. A pre-feasibility study has been completed, and a bankable feasibility study is currently being prepared. As reported in Couch (2008) the plans are for a 10 Mt/y open cut mine to supply, initially, two 15,000 bbl/d liquid product streams together with a power plant with 560 MWe of export power. This is quite separate from the Linc Energy plans.

The transfer of the Linc activity to Arckaringa would facilitate the use of otherwise ‘stranded’ coal there. It would presumably involve some additional exploration work, as the requirements for UCG are more stringent than those for conventional mining and the UCG activity might be in deeper seams than those targeted by Altona. It would also require a new pilot-scale UCG operation to establish the design basis for a commercial-scale expansion in the new coal seam. Amongst the challenges to be addressed will be the hydrogeology of the site and the use and disposal of water as it is in an area where water use allocation approvals are required. As the decision was only made in November 2008, detailed plans have not yet been published, although the area is said to have the potential to support several 100,000 bbl/d UCG/STL plants (Syngas Refining, 2008b; Coober Pedy, 2008).

While the major expansion of Linc Energy’s activity is now planned to be at Arckaringa, it is intended to retain the research and development activity at Chinchilla. It is intended to start up a new UCG generator before the end of 2009. Drilling has already started in the deeper Taroom coal measures. These extend from 250 to 500 m deep, but at the time of writing the exact site for the next trial had not been chosen. Tests are planned to assess the effects on syngas production of the higher operating pressures which will be used, and of the use of oxygen, rather than air, as the oxidant. There will be enhanced reactor cavity

68 IEA Clean Coal Centre and groundwater monitoring, and the re-injection of water/steam will be assessed (Minotti, 2009). With the planning of the new UCG trial, discussions are well advanced on the conceptual design for a 20,000 bbl/d STL demonstration plant. This could provide the basis for a series of similar sized modules for the Arckaringa expansion.

Linc’s international involvements Linc Energy bought a 74% controlling interest in Yerostigaz in Uzbekistan where UCG gas is fed into a PCC power station nearby at Angren, as a supplementary fuel. The Angren site has been in continuous operation since 1961 (Linc, 2009).

Linc Energy have a partnership arrangement with Vietnamese and Japanese companies to assess and possibly develop a UCG activity in northern Vietnam. A MOU was signed in 2008 with the Vinacomin (Vietnamese) and Marubeni (Japanese) companies relating to stage one of the project (Linc, 2008c). Vinacom is the Vietnam National Coal and Mineral Industries Group. The project is discussed further in Section 5.18. At the time of writing it was reported that the contract to undertake the pilot trial in a potential UCG Tonkin development area in the Red river delta, had been signed (ABNnewswire, 2009b).

Linc Energy has also signed a letter of intent with the Xinwen Mining Group in China relating to the development of a UCG/STL activity in the Yinan and Yibei coalfields in Shandong province (Syngas Refining, 2008c).

In May 2009, Linc Energy signed a purchase agreement with GasTech Inc in Wyoming, USA to acquire nearly 40,000 ha of coal tenements in the Powder River Basin at a cost of US$5 million UCG development in Wyoming is discussed further in Section 5.17.1.

5.1.2 Carbon Energy Carbon Energy Pty Ltd (CEPL) was set up to deliver large-scale energy projects based on the cleaner and greener use of coal and has its own IP associated with UCG. It owns leases on a number of blocks of coal in the Surat Basin in Queensland. The target resource is likely to contain between 250 and 600 Mt of high ash subbituminous coal in seams 10–20 m thick.

The CSIRO work on which the CEPL development is based along with the US experience from the Rocky Mountain 1 trial, is discussed in Beath and Su (2003); Beath (2004), and Beath and others (2004). The CEPL technology involves drilling two in-seam boreholes in parallel through a block of coal. At the end they turn towards each other at a point near a vertical ignition well, see Figure 22. There will be a CRIP in the injection well and its retraction should provide good control of the location of the gasification as it moves through the coal panel and thus of the gas quality. The oxidant is oxygen- enriched air.

The long-term development plan, as formulated in 2008, was to: G start with the small-scale demonstration for 100 days in a panel of coal to prove the consistency and quality of the syngas using oxygen as the oxidant. The test has been successfully carried out and has provided invaluable experience with in-seam drilling and the establishment of the necessary underground linkages to facilitate ignition. It has also provided experience with the operation of the CRIP in the injection well. The data obtained during the demonstration is providing the information to facilitate scale-up to a commercial-scale project in a step-wise fashion. With air based gasification some 70 t/d of coal was being consumed, and with the oxygen/steam mix this increased to around 150 t/d (Carbon Energy, 2009a); G as at the Chinchilla trial, the area around the coal panel is being carefully monitored with a series of different wells nearby taking water samples and with piezometers. These make measurements above the reactor level, alongside it, and at a lower level; G enlarge the demonstration to produce enough gas for a 20 MWe power plant. The syngas quality would be assessed to see if it could justify a liquids production facility and the first expansion may be to construct an ammonia unit for the production of ammonium nitrate fertiliser. Either development would generate some revenue; G construct a 2000 bbl/d liquids production facility, again generating some revenue; G build a 34,000 bbl/d liquids production plant, based on the experience gained from the demonstration-scale unit; G carry out the necessary exploration work to identify the best locations for other sizeable operations in the future.

The initial 100-day demonstration was estimated to cost some A$20 million, including setting-up all the necessary site facilities for water, oxygen and LPG storage, in-seam boreholes, monitoring wells together with living quarters for some of the personnel (Mallett, 2008).The projected operations would be the subject of further feasibility studies and assessments based on the experience gained during the trial/demonstration. A further extended production demonstration is planned, which would be a zero profit project, but would generate some income either from operating a small turbine (~20 MWe) generating power, and/or from ammonia production. This would involve an area of around 1 km2 where

Underground coal gasification 69 a) isometric

30 m UCG surface facility 600 m panel length ignition well ~100 m x 50 m spacing

oxygen supply control generator room gas flare boiler and gas collector steam generator

water oxygen and steam supply line natural holding dam surface injection well production well (oxygen and steam) (product) H , CO, CH CO 2 4 2 30 m x 30 m x 10 m block consumed in the demonstration trial 200 m depth of cover

CRIP

direction of burn

coal seam 8-10 m thick

b) plan

UCG demonstration trial buffer zone

seismic lines

PANEL

north - south seismic line exploration holes

monitoring wells

injection and production wells

ignition well

east - west seismic line

PANEL

old ignition well

Figure 22 The Bloodwood Creek layout with parallel-holes CRIP for the 100-day trial (Mark and Mallett, 2008)

70 IEA Clean Coal Centre some twenty UCG panels would fit. A CO2 capture demonstration would be incorporated. This stage would take at least two years to complete, and involve additional capital costs of some A$30 million.

Based on the successful results from the 100-day trial, Carbon Energy has raised the necessary capital (A$32 million) to fund the next stage of the development (Syngas Refining, 2009b). As operational experience is gained with in-seam drilling, with establishing links between the wells and with the CRIP it will be possible to refine some of the design parameters. This will facilitate cost reductions when the facility is expanded. During the eight months of operation to date, the pilot facility has produced a syngas with a heating value of about 6 MJ/m3 when air blown and of 13 MJ/m3 when oxygen and steam were used as oxidant. The gas composition was stable during the trial, and when oxygen blown, the energy content of the methane and ethane (the basis for SNG) formed represented some 60–65% while the H2 and CO components represented the remaining 35–40%. These results validated plans for maximising the production of chemicals and liquid fuels in addition to the generation of electric power.

At the time of writing Carbon Energy proposes to commission a 5 MWe power generation unit using syngas during 2009, and to increase the generation capacity to 20 MWe during 2010. During 2009 Carbon Energy announced a tie-up with ZeroGen to capture the CO2 from the 20 MWe unit and to pipe it to Springsure in central Queensland where it would be stored in the Northern Denison Trough at depths up to 2 km. The combined UCG/CCS demonstration would be the first such project anywhere in the world (Stockwatch, 2009)

The longer-term plan is to set up the Blue Gum Energy Park with facilities for: G power generation (up to 150 MWe) initally, expanding to 300 MWe; G an ammonia plant; G chemicals manufacture; G transport fuels production; G synthetic natural gas production; G commercial and administration facilities.

The large-scale plant could either produce 1000 t/d of ammonia, >1000 t/d of methanol and/or 10,000 bbl/d of liquid transport fuels. This stage would cost more than A$1000 million in capital expenditure. Carbon Energy are proceeding in a careful step-wise fashion, and each development is firmly based on the evidence obtained from the test and evaluation work. The expansion to commercial- scale operations is likely to be completed during the next five to seven years. The current phase is the construction and operation of an extended demonstration plant based on the results from the pilot. As the work proceeds, the various models developed by the CSIRO can be validated and can become increasingly useful tools (see Chapter 7).

The CSIRO and Carbon Energy have published a number of useful and descriptive papers which discuss the various aspects of UCG which have been used and quoted throughout this study and which contribute to the necessary public debate about UCG development in a variety of places (Beath and Davis, 2006; Mallett and Mark, 2007; Mallett, 2008).

5.1.3 Cougar Energy Cougar Energy Ltd was set up in 2006, and is working on setting up projects in Queensland and Victoria. Cougar Energy (UK) Ltd operates in Pakistan, India and Europe. It has the offer of a lease in Sindh Province, Pakistan, covering 47 km2 of the Thar coalfield (for background information on coal in Pakistan, see Couch, 2004). For possible Indian development, it has a MOU with Essar Oil and Exploration (Walker, 2008).

Cougar plan to use the ␧UCG technology involving vertical wells and using hydraulic fracturing and reverse combustion linkages, which is licensed from Ergo Exergy. It is based on extensive Russian experience. At Kingaroy, Queensland (near the Tarong power plant), drilling has confirmed that there are two coal seams more than 150 m deep and each >10 m thick, over an area of 4.5 km2. These would provide the potential resource for a 400 MWe power plant to operate for more than 30 years using UCG. Preparations are being made for a pilot burn to establish the process parameters for development so that the project costings for the power plant operation can be firmed up. Site characterisation was completed in February 2009 and it is planned to drill the wells and bring in the necessary equipment so that the pilot burn can start in July 2009 (Cougar Energy, 2009). In a preliminary feasibility study the capital cost for the 400 MWe power plant is estimated to be A$500 million, and when operational, the site would return a net cash flow after interest payments of around 80 million A$/y. A 200 MWe unit, which is the first stage of the development, is due to become operational in 2012.

In a 50/50 Joint Venture with Victoria Coal Resources Pty Ltd, Cougar are looking to exploit large brown coal deposits in southeast Victoria which lie under a limestone layer. Seam depths are from 100 to 700 m, with thicknesses 10 to 70 m. These have potential for major UCG power generation and/or liquids production.

Underground coal gasification 71 5.1.4 Altera Resources A company in Western Australia, Altera Resources, is reported to be set to investigate and assess various possibilities for UCG. They were interested in acquiring Clean Global Energy Pty Ltd which is a coal mining company which has access to IP for UCG (WA Business News, 2008), although they subsequently pulled out of the deal (Beath, 2009).

5.1.5 Liberty Resources Liberty is acquiring extensive Exploration Permits for Coal (EPC) Applications in Queensland which cover coal resources which are potentially suitable for UCG (Liberty Resources, 2009). The exploration targets are mainly in the Waratah region of the Galilee basin which lies northwest of the Surat basin where other UCG projects are being developed. The area is thought to have coal resources in the 205–415 Gt range. An initial resource of 338 Mt has already been identified. In addition, Liberty is looking for EPCs covering some western parts of the Surat basin.

A considerable amount of work remains to be done, including: G drilling and other exploration, followed by the technical assessment of selected areas; G classifying the different parts of the resource as being suitable for conventional mining, for UCG, for CBM recovery or for none of these options; G funding a UCG pilot operation on which to base the design and costings for larger-scale activities; G developing a commercial-scale plants based on the syngas product to generate power and/or chemicals and liquids fuels.

5.1.6 Metro Coal In an overview of Australian UCG developments, Green (2009) included Metro Coal who are said to be looking at three UCG projects in 130 to 300 m deep seams. In a subsequent press release, Metro Coal announced that drilling at their Juandah project in the Surat basin has confirmed a potential coal resource of 170 Mt, sufficient to fuel a UCG-STL plant producing around 20,000 bbl/d of liquid fuels (ABC News, 2009). Exploration is continuing.

5.2 Brazil

Coal provides just over 6% of Brazil’s energy, and in terms of power generation, it is only 1.6%. This is partly because 85% of Brazilian electricity comes for hydropower – which is potentially risky in terms of supply security if climate change affects the rainfall significantly.

Brazil’s coalfields are mainly in Parana, Santa Catarina and Rio Grande do Sol, all in the southern part of the country and near to the coast. There has been no geological surveying for coal since 1982, and as a result there is a need to review and update all the available data. A number of the coalfields are thought to extend out on the continental shelf under the Atlantic ocean.

Alongside the establishment of storage sites for CO2, and investigations into the recovery of CBM, UCG should be looked at in order to exploit some of Brazil’s deep coal resources and unmineable coal seams (Zancan and Cunha, 2007). This will involve some selective additional geological surveying to establish potential sites for UCG exploitation which will take some considerable time. Brazilian geological knowledge (Dantas, 2008) includes some detailed assessments of the coal deposits in the Rio Grande do Sol state in southern Brazil. Geological storage sites for captured CO2 are discussed by Ketzer and others, 2007.

The challenges in Brazil are to set the parameters concerning reactions, burning control, the oxidant used, syngas quality control, UCG process simulation, laboratory and pilot-scale results validation and process efficiency studies. The Clean Coal Technology Center is supported by both the mining industry and state and federal government. It has been developing researches in geology, mining and the environment and intends to focus activities on conversion processes, including UCG. Discussions have already been held on regulatory issues, and in Brazilian Law 11.909 dated 4 March 2009, it is clearly stated that gas produced from coal belongs to the owner of the mining concession (Zanuz, 2009). This is a valuable first step in facilitating UCG development.

5.3 Canada

Canada has very extensive coal resources, some of which are likely to be suitable for UCG. The head office of Ergo Exergy Technologies Inc is located in Montreal. Ergo Exergy licence their proprietary ␧UCG technology which is based on the experience in the USSR, to a number of other companies.

A review of the energy situation in Canada, and the possible relevance of UCG was discussed in a paper

72 IEA Clean Coal Centre by Blinderman and Maev (2003). Laurus Energy is the Canadian company who have licensed ␧UCG technology. They are assessing the suitability of coal deposits in most of the provinces in Canada. In 2006 they reported the evaluation of a deposit near a power plant in Nova Scotia where the syngas produced would displace both imported coal and petroleum coke thus significantly reducing SO2 emissions.

In 2008 at the Underground Coal Gasification conference in Houston, Laurus Energy made a presentation about the potential for UCG use, but made no reference to specific or imminent Canadian developments (Wilcox, 2008). At the end of the year it was reported that Laurus had some funding which would enable it to pursue operational permits either in the Canadian province of Alberta or in the USA (Bradbury, 2008).

Early in 2009 a project to set up a pilot test in a deep coal seam in Alberta was announced by Swan Hills Synfuels. The facility is located some 250 km north of Edmonton near an oil sands project that will have a very substantial demand for gas as a source of heat. The pilot test is estimated to cost some C$30 million to which the government of Alberta would contribute nearly C$9 million through the Alberta Energy Research Institute. The project would consist of a single pair of wells in a seam roughly 1400 m deep (Green Car Congress, 2009; Teel, 2009) and would use an enriched oxygen/steam mix as the oxidant to produce a high heating value syngas. It taps into the Manville coal formation which is a seam stretching some 500 km from Grande Prairie to Calgary. The wells are reported to consist of one vertical well intersecting with an in-seam borehole (Syngas Refining, 2009c). If successful, the development could produce a suitable fuel for power generation and/or, because of its depth, it might provide the basis for producing a SNG. This pilot is the deepest UCG test to date, and there is very limited experience with using UCG at depths below 300 m. Drilling costs will be significant at this depth but the higher operating pressure of the reactor could result in a higher CV gas. There is relatively little risk of groundwater contamination and with the higher pressure, CO2 storage in adjacent strata would be facilitated by the operational pressure of approximately 14 MPa.

If the initial trials are successful, it is intended that a commercial-scale unit would produce some 2000 t/d of CO2 which would be used for EOR (NorthAm Oil, 2008). A commercial facility which would produce just over 900,000 m3/d of syngas was estimated to cost some CAN$400–600 million. It may also be possible to investigate whether the resultant deep cavities formed during UCG might be used for long-term CO2 storage.

At the time of writing a further development has just been announced and Nordic Oil and Gas Ltd are preparing an application to the Alberta government for permission to undertake a pilot UCG trial in coal measures near Drumheller (Nordic, 2009). If it goes ahead this would be Canada’s second such pilot.

5.4 China

China has huge coal resources, and production has grown from 1 Gt/y in 2000 to 2.5 Gt/y in 2007, making China by far the world’s largest producer and user of coal. In a market assessment of the potential for UCG in China, it was stated that there is just over 1000 Gt of ‘discovered’ coal down to 1000 m deep. The total amount down to 2000 m deep is thought to be more than 5000 Gt, so there is enormous potential for energy recovery from very deep resources. Thus research and development is looking towards the recovery of energy from these very deep deposits as well as from some of the shallower coal.

China has about a hundred graduate students and fifteen PhDs working on various aspects of UCG at a dedicated research centre at the China University of Mining and Technology, Beijing (CUMTB). During the past twenty years, some sixteen UCG trials have been carried out, initially to recover coal/energy from abandoned coal mines. These followed on from earlier trials which started as long ago as 1958. The coals involved have varied from gas coal and fat coal to anthracite (according to the Chinese classification system which is outlined in Couch, 2006). The product syngas has variously been used in industrial boilers, for power generation and for ammonia synthesis. There is a considerable emphasis on the potential for chemicals production from the syngas.

UCG using boreholes The Xinao company is taking a lead in UCG development through their subsidiary ENN Group Co Ltd (Gan and Sung, 2008). Recently there has been a pilot UCG project in Inner Mongolia with injection and production wells drilled into previously undisturbed coal. Initially there were seven injection and production wells which were first fired in October 2007, using air. The gas production from the pilot was 150,000 m3/d with >60% CO+H2. The plant is located at the Gonggou coal mine in Wulanchabu city, and is gasifying a 200 m deep seam (Red Orbit, 2007). ENN is planning to expand UCG production substantially by 2020 (Feng Chen, 2008), and are using a Chinese version of CRIP. Two new gasifiers were set up in February 2009, each with a capacity for producing 500,000 m3/d of syngas for a two-year period. The syngas will be used in two 10 MWe generator units which have already been set up, and it is intended to start gasification using oxygen in mid-2010 to supply syngas to a 20,000 t/y methanol plant (Feng Chen, 2009).

Underground coal gasification 73 5.5 EU HUGE project

Hydrogen oriented underground coal gasification for Table 7 The consortium partners for the HUGE Europe (HUGE) is a major project being supported by project (Palarski, 2007) countries from the EU, and with a contribution from the Ukraine Mining National Academy. It aims to utilise a wide range of experience to explore the possibility of the Glowny Instytut Gornictwa Poland direct in situ gasification of coal to produce a hydrogen- rich syngas (Rogut, 2008). The consortium members are Kompania Weglowa SA Poland shown in Table 7. Politechnika Slaska Poland A three-year programme started in 2007. The project will BOT Górnictwo I Energetyka SA Poland explore the technology for hydrogen production using UCG in what is called a dynamic geo-reactor. It is Poltegor Institute Poland intended to address CBM recovery from the coal seams, together with CCS back into the deposits. The sites for Delft University of Technology the Netherlands some possible demonstration plants will be chosen through computer modelling and simulation, and at this Universität Stuttgart Germany stage the project is entirely a ‘paper’ exercise. The intention is also to address other parallel issues, Institute of Chemical Process Fundamentals Czech Republic namely: G Institut Scientifique de Service Public Belgium the direct capture and storage of CO2; G protection of deep water resources against pollution; The UCG Partnership Ltd UK G the reduced use of pure oxygen for gasification; G the exploitation of stranded lignite and deep National Mining Academy Ukraine bituminous coal deposits; G to share the results from UCG testing with CCS development; G to integrate this CCT with the development of the hydrogen economy.

Its main targets are to: G determine the conditions under which hydrogen will be the major gaseous product from UCG; G assess the opportunities for in situ CCS; G develop a proof of concept statement for a pre-feasibility study of a demonstration-scale project as a Joint Technology Initiative amongst the participating parties.

The HUGE project consists, at the moment, of a series of integrated theoretical studies which could result in practical assessment work and specific feasibility studies, if the conclusions are encouraging. It targets the set-up of a reliable knowledge base for the cost effective generation of hydrogen using UCG. The project focuses on the critical evaluation of process parameters and geological conditions required for the successful and safe conversion of coal resources to hydrogen and their subsequent matching to suitable European coal deposits (Rogut and Steen, 2008).

The consortium has a mining concession in Upper Silesia covering an area of over 600 km2. A pilot project is planned using the Super Daisy Shaft system described in Section 3.2.6. which is designed to recover energy by UCG from a circular area of about 15 km2. It would use oxygen and steam, and reaction conditions would be maintained so as to maximise hydrogen production. It does not seem likely that any practical demonstration would be possible for several years as the Super Daisy Shaft concept is as yet untried in coal, and it is likely to be some time before the paper studies currently being carried out can be usefully applied to provide the basis for a feasibility study.

Poland, where the HUGE project is primarily located, has a long history of interest in UCG, see Section 5.11.

5.6 India

The Indian government has taken a considerable interest in UCG. Under the auspices of their Principal Scientific Adviser a Status report on underground coal gasification was prepared (Government of India, 2007). This reviews international activities in the past and outlined the potential for development. The report then looks at the opportunities in India.

UCG had been considered since the early 1980s for the exploitation of unmineable coal which had been discovered at depths below 600 m during oil and gas exploration in both Gujarat and West Bengal. The Oil and Natural Gas Corporation (ONGC) prepared a feasibility report on a UCG prospect at Kalol, Gujarat. An exploratory well was drilled in Mehsana, Gujarat, in 1986 to a depth of 1005 m to acquire geological and hydrogeological data. This encountered a number of coal seams between 745 and 940 m

74 IEA Clean Coal Centre deep, and a 3D seismic survey was carried out. Based on the results, a second exploratory well was drilled in a fault-free area. The findings were further assessed, but no funding for a pilot trial was forthcoming.

In 2006 a workshop on UCG was held, hosted jointly by the Ministry of Coal and the US DOE. As a result, at least three pilot projects are being planned. The Status Report was written and a Roadmap for development is being prepared. Since UCG is not yet an established technology on a commercial scale, this seems to be the appropriate way to proceed. Development proposals can take into account the lessons learned from the current trials in Australia and South Africa which are intended to provide the basis for commercial-scale operations.

In view of the nature of UCG, India regards the activity as being similar to CBM recovery and to natural gas based operations, rather than to conventional coal mining. It therefore intends to develop UCG under the Petroleum and Natural Gas Rules, 1959, with a minor modification to the definition of ‘Petroleum’.

India recognises that it would be necessary to allow foreign companies to set up demonstration/ commercial UCG projects for the utilisation of deep coal deposits. This could be done more readily under the legal and regulatory framework governing CBM recovery where there is no restriction on the sale of the gas product at market prices. The government may consider setting up a tax-free regime for a period of seven years, similar to that applied to CBM development, to encourage public-private partnership for UCG development.

In the Status report the potential inputs from a number of major industrial enterprises and of government departments is discussed. These comprise the: G Oil and Natural Gas Corporation Limited; G Directorate General of Hydrocarbons; G Essar Oil Limited; G Indian School of Mines; G Reliance Industries Limited; G Singareni Collieries Company Limited; G Bharat Heavy Electricals Limited; G Coal India Limited; G Neyveli Lignite Corporation Limited; G Mineral Exploration Corporation Limited; G Central Institute of Mining and Fuel Research; G Central Mine Planning and Design Institute.

Following the Status report referred to above, the government has allocated a number of coal blocks for possible exploitation using UCG.

In discussing the potential contribution from BHEL to UCG development, Nandakumar (2006) estimated that to support a 250/300 MWe power generation unit for some 30 years using UCG a bituminous/subbituminous coal reserve of some 30–40 Mt would be required, or for a lignite, 50–60 Mt. The US-India working group reported that a study would be undertaken in Rajasthan by the Neyveli Lignite Corporation to assess the possibilities for an UCG development (US-India WG, 2006).

At about the same time, the National Thermal Power Corporation (NTPC) published a study on the Economics of power generation with UCG (NTPC, 2006). NTPC also estimated the necessary coal reserve for a 250/300 MWe unit as being around 40 Mt. The largest non-coking coal reserves at depths of 300–1200 m thought to be most suitable for UCG, are located in the Godavari Valley, Andhra Pradesh, and in Raniganj, West Bengal. Two areas with potential for UCG were identified as being Mehsana (in Rajasthan) and Gondwana (covering the Godavari Valley and Raniganj). Both the Gas Authority of India (GAIL) and the Oil and Natural Gas Corporation (ONGC) are involved in UCG development.

In an extensive paper, Khadse and others (2007b) discuss the potential for UCG applications in India, and highlighted the need for some regulatory changes that were necessary to facilitate its use. Indian coal resources are reviewed in detail, and a possible coal block containing lignite was identified. The modelling work carried out by the Indian Institute of Technology (IIT) in Mumbai is discussed in Chapter 7.

The Australian government is supporting UCG development in India (CMTF, 2008) and in the next stage of the programme it is proposed to undertake a feasibility study and detailed planning during 2009 for a UCG demonstration in the Godavari Valley in Andhra Pradesh. This is being undertaken in conjunction with Carbon Energy (see Section 5.1.2). It is reported that Singareni Collieries have identified a coal block in the Valley with coal seams ranging from 5 to 15 m thick at depths between 300 and 600 m for possible exploitation (Syngas Refining, 2009a).

Underground coal gasification 75 5.7 Ireland

A preliminary screening study of the possibilities for using UCG in the Kish Basin off the coast from Dublin is being carried out by VP Power Ltd. This forms part of a larger project evaluation study which needs to consider first whether the coal geology is potentially suitable for UCG (Mayne, 2009).

5.8 Japan

Japan has substantial interests in coal in other countries, as well as some resources on its continental shelf. It has included UCG in its future research plans and has been maintaining a low level programme for many years. The University of Tokyo has undertaken technical and economic studies of UCG and maintains a watching brief on behalf of NEDO (Burton and others, 2006).

Based on the work by the US DOE in the 1970s and 80s, Shimada and others (1996) presented cost estimations comparing the costs of using the extended linked wells method with CRIP. An area on Hokkaido was selected where there is a seam 3–7 m thick at an inclination of some 30° and a depth going from 150 to 350 m.

It is reported that in 2008 a team of up to twelve companies, including the Mitsubishi Materials and Marubeni Corporations are developing UCG technology with a view to commercial application in some five years time (Green Car Congress, 2008). A test facility at a domestic mine is proposed.

5.9 Kazakhstan

There is interest in Kazakhstan in the application of UCG to the Tobol Chernigovskye lignite deposit (Tobol, 2009; Gaston and Franklin, 2009). The deposit is located in northern Kazakhstan, some 120 km from Kostanay. A number of partners are involved, including Promgaz, the Skochinsky Mining Institute, Kazgeology and Centergeolanalyt, and the Institute for Complex Subsoil Exploration. A two-stage project is in progress, comprising: G geological surveying from 2009-12 to establish the extent and nature of the deposit, at a cost of approximately US$1 million; G setting up the first UCG wells in 2013, at a cost of approximately US$37 million.

5.10 New Zealand

Following the earlier small-scale trial work in the 1990s, a major mining company Solid Energy New Zealand (SENZ) has licensed the ␧UCG technology from Ergo Exergy, and is carrying out resource characterisation to assess the potential viability of an UCG project (Pearce, 2008).

The trial took place at the Huntley colliery in 1994 and used the CRIP technique with in-seam wells as used at Rocky Mountain 1 in the USA. The test was in a shallow seam (<200 m deep) and lasted for just 13 days. Some 80 t of coal was gasified.

The coalfields in New Zealand are geologically complex, and were formed in tectonically and depositionally active settings. There are widespread and diverse faulting patterns and styles, and seams may be folded. They are sometimes laid down on an undulating basement surface with multiple seams which split and merge, and are commonly associated with complex hydrogeology. The overburden is typically weak, consisting of clay-rich strata and unconsolidated soils. In addition, coalfields are often overlain by high value farmland, areas of cultural significance, rivers and lakes – and by existing infrastructure such as roads and buildings.

This geological complexity has presented considerable technical challenges to the successful extraction of coal from conventional mines, and unique mining techniques have been developed including rib pillar and bottom-coal extraction and hydraulic mining. The use of ␧UCG technology for energy extraction is seen as a mining method which complements Solid Energy’s current operations. It has the potential to allow low cost exploitation of coal that is not technically or economically feasible using other methods.

SENZ is using a combination of the following techniques to identify suitable sites for UCG development based on experience in designing conventional mines, including: G data management, with a central database for all drill-hole data, covering lithology, coal quality, geophysical logs, drill-hole survey data, geotechnical testing and hydrogeology; G the coring and core descriptions provide a wealth of information about coal quality and characteristics, as well as the seam thickness; G geophysical drill-hole logging provides a continuous record of in situ measurements and contributes to determining rock strength, stress orientation, fracture mapping and dip determination

76 IEA Clean Coal Centre and mapping. Various logs are kept relating to radiation, acoustic and electrical properties; G the results are modelled, with the intention of preparing the design and layout for an underground mine, and in the future the information might be used to model the layout of UCG panels and access points; G hydrogeological modelling to assess the response of the groundwater systems to underground activity (either mining or UCG); G well test analysis using pressure derivatives (for example the logarithmic time rate of change of the pressure) together with non-linear regression analysis, as well as conventional log–log and semi- log straight-line methods; G 3D seismic which allows underground hazards to be accurately and reliably identified.

Using this expertise, SENZ have identified several potential sites where UCG might be applicable in order to ‘mine’ the coal. More detailed investigations are ongoing at the top ranked site with a view to developing commercial proposals for exploitation (Pearce, 2008).

5.11 Poland

Laboratory tests were carried out in 1950, followed by some underground experiments at the Mars mine in 1953. Subsequently some UCG modelling was undertaken in the early 1980s. Work on the possibility of using UCG in Poland was resumed in 2007 (Palarski, 2007) and much of this is associated with the EU HUGE project, see Section 5.5.

The proposed Super Daisy Shaft project would be based around Rybnik in Upper Silesia in Poland’s major hard coal area (Palarski, 2007; Walker, 2000) see Section 3.2.6. In a separate paper discussing the research agenda for the Polish mining industry, Karaÿ (2007) outlines the possible involvement of KGHM Cuprum R&D Co in the government Joint Technology Initiative for Clean Coal in Poland using the Super Daisy Shaft system for lignite gasification.

5.12 Russia

While the USSR had by far the largest number of UCG projects from the 1930s to the 80s, most only provided a low grade fuel gas, and because many were in shallow coal, gas leakage was a significant problem. In addition, studies of the projects carried out during the late 1950s and early 60s have revealed that groundwater contaminants resulting from gasification were widespread and persistent, even up to five years after production had ceased (Liu and others, 2007). The longest running UCG activity has been at Angren, which is now in Uzbekistan.

Even though there were many tests and developments, some of which have been described as ‘commercial’ (see Chapter 4), the total amount of coal gasified during the whole period was only some 15–20 Mt. The technology used in the past is being applied by Ergo Exergy Technologies with their ␧UCG developments, based on multiples of two relatively closely spaced vertical wells, linked by hydrofracturing and/or reverse combustion. This method was used in the first trial at Chinchilla in Australia and is currently being applied at Majuba in South Africa.

Much of the experience in Russia seems to have been either in fairly shallow seams of low rank coals which are nearly horizontal, or in steeply dipping seams of black/bituminous coal.

The principal positive results from the Soviet programme were (Gospodinova, 2008): G the technology using vertical wells with hydrofracturing and reverse combustion to establish the links was established in several locations; G the process widening of narrow-drilled channels underground (150–200 mm wide) up to 1 m diameter was developed; G the mechanisms associated with rock movement and hydrogeological change were studied; G operating conditions to minimise environmental impact were identified.

However, there were a number of drawbacks, including: G insufficient process control resulting in unstable syngas composition; G low capacity because of restricted production wells and the need for a large number of such wells; G irregular and chaotic motion of the injected gas underground, resulting in the partial oxidation of the syngas before discharge.

Promgaz are currently promoting new UCG developments in Russia (Karasevich, 2008; Zorya and others, 2009). In particular the new Russian technology uses in-seam boreholes, and CRIP-type operation. Movement of the oxidant injection point is proposed with ‘streaming’ gasification in a broadly similar way to the method used at Bloodwood Creek in Australia.

It is claimed that with the new technology, the distance between inclined and in-seam injection and

Underground coal gasification 77 a) Near horizontal seams

production injection well well

ø250 mm ø200 mm 100 m

50 m 50 m 300 m

ignition well ø150 mm water-removing well water-removing well ø200 mm

production injection well well

ignition well

water-removing well linking horizontal well b) Steeply dipping seams water-removing well inclined injection well vertical inclined injection production well well inclined production well

coal seam

gasified inclined space injection well

gasified space

vertical vertical injection water-removing well well

Figure 23 Schematics of the new Russian technology for UCG (Zorya and others, 2009)

78 IEA Clean Coal Centre production wells can be increased to 50 m with the use of in-seam boreholes to provide the links. Across a 300 m block, only seven wells are needed, three for injection and four for production see Figure 23. Only one vertical ignition well is needed to get the gasification started. This pattern should result in significantly reduced drilling costs and greater certainty when establishing the linkages between the injection and production wells.

Between the old and new constructions, the following comparisons are made (Karasevich, 2008; Zorya and others, 2009): G in the old construction, to a shallow coal seam, the inclined borehole carrying the product syngas was cased, although where the hole is in the seam itself, it is not cased. These holes are at a distance of about 30 m apart. Three lines of vertical holes are drilled to inject the oxidant (air) into the system. These are 30 m apart across the field (alongside the product holes) and 100 m apart along the line of the in-seam production boreholes; G in the new construction, there is an in-seam borehole making the linkage(s) between the injection wells (which are cased for their full length to prevent premature oxidation/burning of the coal). In addition, the air/oxygen supply point can be moved/relocated, and it is withdrawn progressively in order to burn consistently along the seam. It operates in much the same way as a CRIP and in a broadly similar way to the method used at Bloodwood Creek in Australia. It is claimed that process sustainability and stability would be greatly improved. With air injection, a product syngas with a heating value from 4 MJ/m3 is attainable, while with oxygen injection it can be 11 MJ/m3. The proportions of CO, H2 and CO2 should be more readily controllable, and up to 90% of the coal in the seam can potentially be gasified.

A trial of the new technology is planned in the Kuzbass (Donetsk) region which carries over into the Ukraine, in a hard coal seam some 300–400 m deep and 8–10 m thick (Kreynin, 2009). This would use directional in-seam drilling to make the linkages between the various injection and production wells as shown in Figure 23. The technology is said to be applicable to both near horizontal seams and to steeply dipping ones, in both cases using the ‘streaming’ method of cavity development.

5.13 Slovakia

Early UCG tests were carried out in Czechoslovakia (as it then was) in 1956 in a coal seam which was only some 20–25 m deep and covered with a sand loam and clay. The seam was 3.5–4 m thick. The product gas had a heating value of 1.6–3.4 MJ/m3, and there would have been considerable gas leakage. Further tests at Laksaraka Nova Ves in 1961 encountered technical problems and the programme was not completed. After that only paper studies were undertaken.

From 2007 in Slovakia a national research programme into UCG was initiated, using laboratory apparatus, with an expressed interest in joining-in with an international project undertaking field trials if such an opportunity could be found (Kostúr and Kaïur, 2009). The HBP Co in Slovakia might have suitable sites. It has three active collieries with only about 35 Mt of exploitable coal using conventional mining techniques. The coal is a lignite with 23–35% moisture; 20–35% ash and a heating value of 9–12.5 MJ/kg. The use of UCG could release the energy from unmineable resources and there are geological resources of approximately 1 Gt.

5.14 Slovenia

Some extensive assessment work has been carried out on the possibility of using UCG in the mining area near Velenje. This was reported at a DTI International Workshop in London in 2003 (Veber, 2003). There is additional information about the coal reserves at Velenje in Veber and Dervariè (2004).

An earlier assessment had been made in 1985, and further work made a detailed deposit evaluation including seam thickness (which was between 60 and 160 m) at a depth between 400 and 600 m. The roof strata consists of mudstone with layers and lenses of sand while the floor is principally clay, silt and sand. The coal is a young lignite between 2.5 and 3 My old, with a moisture content of 20–45%, ash 3–30% and LHV of 7.5–13.5 MJ/kg. Near existing workings, two possible areas for UCG were identified (Veber, 2003). The assessment included a detailed study of the hydrology of the deposit, and the implications of undertaking UCG operations near existing workings.

The study also looked at the coal characteristics, and the potential mineral transformations that might take place in a UCG reactor. These could affect process efficiency, gas quality, cavity development and the presence of contaminants.

In some parallel work, the requirements for process control were considered and a shortcut method for controlling the underground reactor proposed, based on thermodynamic equlibrium considerations. It is based on the following: G the inlet reactants can be controlled and measured, both in terms of composition and pressure;

Underground coal gasification 79 G the outlet gas composition and pressure can similarly be measured.

What is not known is the gasification temperature (and its distribution underground), the water influx and the amount of coal consumed. It is proposed that some of the parameters measured during the coal characterisation may be useful in predicting the product gas composition.

It is proposed that by coupling the equilibrium thermodynamic model with an appropriate minimisation algorithm, the unknown fluxes into the UCG reactor could be assessed based on the measured product gas composition, known feed conditions and the estimated ‘equilibrium’ gasification temperature.

It did not appear that any further work has been done since 2003 follow-up the initial investigations at Velenje (Berïiï, 2008; Zapušek, 2008), but Zavšek (2008) reports that interest has been revived in 2008, and that the prospect of using UCG at the colliery is being revisited.

5.15 South Africa

There are two active UCG developments in South Africa, one which was initiated in 2001 by Eskom with pilot plant work in 2006, and the other by Sasol with a pilot trial scheduled for 2009. In an overview of the longer-term energy requirements in the country and the part played by coal, Zieleniewski and Brent (2008) present a cost-benefit model for assessing the possible deployment of UCG on a wider scale. The paper highlights the possibilities of utilising otherwise unmineable coals of which South Africa has a huge resource. The current trials will hopefully contribute to a better understanding of where UCG might provide useful energy in the future.

5.15.1 Eskom’s development at Majuba The main current development in South Africa is at Majuba in Mpumalanga where there is an existing 4110 MWe coal-fired power plant located near a substantial coal deposit which proved difficult to mine by conventional methods. The plant has three units which are water-cooled, and the other three are dry- cooled, reflecting the shortage of water as a local resource. As the cost of bringing in coal to the plant by truck and rail is substantial, there is interest in the possibility of using the energy from the local coal deposit to either replace or at least supplement the coal coming in from elsewhere in the country. The Majuba UCG site is owned and run by Eskom while the UCG technology used is ␧UCG licensed from Ergo Exergy Technologies in Canada. This is based on Russian practice and uses vertical wells linked by hydrofracturing and/or reverse combustion, as discussed in Sections 3.2.1 and 3.3.1. The Majuba development uses air-blown UCG.

The principal coal seam at Majuba is the Gus Seam, which lies between 250 and 380 m deep and has reserves of some 1 Gt. There is a coal sequence resulting from the late Carboniferous to the Jurassic with a change of climate from the glacial, through temperate to dry desert. The basin further comprises lava remnants and is associated with dolerite intrusions (dykes and sills). The Gus seam varies in thickness from 1.8 to 4.5 m thick (de Olivera and Cawthorn, 1999). In spite of extensive exploration before the mine was opened and the power plant built, conventional mining of the coal proved to be too difficult and expensive. Obviously for the pilot tests and for the demonstration stages of UCG, the most convenient and potentially successful areas will have been selected with a view to possible commercial- scale development.

The coal was not mineable using conventional underground methods, because it is broken up by vertical structures. For underground gasification, variations in the coal quality/properties have been encountered but have not yet proved to be problematic. Past volcanic activity will have implied that close to the intrusions, the volatiles have already been driven out of the coal, and in some cases the coal could have been completely burnt. It is expected that the lack of volatile matter will retard UCG, and if the intrusion is substantial, then the heat effects could even stop UCG. Horizontal drilling is one of many ways to locate the dykes, and a directional hole has been drilled serving the dual purpose of exploration and of availability for future use during production (Van der Riet, 2009).

The UCG project was initiated in 2001. A pre-feasibility study in 2003 indicated the potential for development, and a detailed site characterisation was carried out by mid-2005. This confirmed that there was potential for a large-scale operation. A research programme and pilot burn resulted in the production of some 3–5000 m3/h of syngas which was initially flared. It was subsequently fed into a converted diesel generator, where it was successfully used to generate 100 kWh of electricity (Van der Riet, 2008). The pilot plant started operation in January 2007, and is still operational with a cumulative production period of some 29 months at the time of writing. The continued successful operation of the pilot led to the approvals given for a larger-scale demonstration plant.

During the development there were a number of challenges, which seem to have been very much what one might expect when trying out something new. Some stemmed from the geological setting of the coal with its volcanic dolorite intrusions. There was initially insufficient geological and hydrogeological

80 IEA Clean Coal Centre exploration data. However, experience has shown that the technology can tolerate some faulting or displacement by dykes because the coal panels developed are modular (Van der Riet, 2008). This is presumably because the panels can be located to avoid any problems.

Compared with the initial estimates made, there was some cost escalation and time creep, associated with equipment availability leadtimes and the time taken to set up the necessary analytical services (Gross and Van der Riet, 2007). Considerable care has been taken to monitor any impact from the pilot burn on groundwaters, and this will continue as the project expands to cover a much larger area (see Section 6.4.1).

During the early stages of the work, as more data became available and more experience was gained, the plans for possible commercial development were changed several times. The plan as presented at an UCG conference in Houston in 2008, is outlined in Van der Riet and others (2008).

Eskom is now embarking on the demonstration of the technology on a larger scale, and the current proposals are to: G develop multiple wells, and put in a bigger pipeline to take syngas to one of the 710 MWe boilers at the adjacent Majuba power station. It is intended initially to cofire this with the equivalent of up to 6 MWe capacity in early 2010, using 15,000 m3/h of syngas. This cofiring would continue until mid-2013; G engineer, procure and construct a 40 MWe demonstration unit, using syngas from several wells with the aim of commissioning it by mid-2013 (the second phase); G while this work is going on, the engineering design would be undertaken for a series of six 350 MWe commercial power generation plants which would come on-line progressively from late 2017 to early 2020 (third phase). Procurement and construction would take place from 2014 onwards (Van der Riet, 2009).

The second phase envisages increasing syngas production up to 105,000 m3/h which will provide the fuel for an on-site 40 MWe OCGT demonstration-scale generator, or could be cofired in the existing boilers in the event that the gas turbine is not operating or under maintenance. The gas turbines would be approximately one third of the size of the gas turbines to be used in the commercial plant, and the size was deliberately chosen to facilitate proof-of-concept and provide final design data for the commercial plant.

Based on the pilot results to date, it would require 20 well systems to produce 105,000 m3/h for this unit, including a little spare capacity. Well linkage rates have proved to be quite quick, and achieving 1 m/day at 5 MPa air pressure is quoted as being common elsewhere.

Using the operational data gained, detailed design work can be carried out and costings updated for larger-scale development. The long-term third phase plan is for the production of syngas to feed a new 2100 MWe IGCC plant on-site, but the developments will in practice take place step-wise with careful review at each stage. It would be based on six 350 MWe units, each requiring some 630,000 m3/h of cleaned syngas (hence 3,800,000 m3/h in total) and consisting of three 120/130 MWe turbines. It would involve six separate (but complementary) gas generation fields whose exact configuration would be decided and based on the results from the demonstration programme outlined above. The implications relating to water use may become a critical factor, although this is not yet an issue. The modular design of the development which is inherent in the Eskom approach should lower the risk involved while ramping production up to a commercial scale (Van der Riet, 2009).

Various stages connected with the commercial plant have already been started, including the Environmental Impact Assessment (EIA), permitting for the necessary mine development plan, land acquisition and partnering with an appropriate engineering contractor. There will be technical feedback relating to gas quality and the ease (or otherwise) of setting up the necessary wells in different parts of the strata, which will feed into the project plan. The need for gas cleaning will also be assessed and appropriate facilities provided.

However, skills and equipment availability are emerging as possible constraints. The overburden includes some very hard dolerite materials which can be drilled with percussion drilling, but drilling problems have been encountered in instances where the dolerite is weathered and crumbly. This was researched and has since been resolved (Van der Riet, 2009).

Casing and sealing the holes also presents challenges (Van der Riet and others, 2008). The Eskom project has focused on gleaning techniques from the oil and geothermal industries and adapting these for UCG drilling. There are always trade-offs between costs and project scheduling, and the issues surrounding the possible hiring of expensive oil drilling expertise for some of the work reflects this.

Only a limited amount of information has been published about the operations at Majuba. The coal seam used initially lies some 300 m underground and is some 3–5 m thick. As at other sites using the LVW method, it is likely that in establishing the link between injection and production wells, and how far apart

Underground coal gasification 81 they can be there is a lot of trial and error. Much of the process is initially empirical and related to the particular site and to the location within the site. However, armed with a substantial body of data, sophisticated modelling techniques are now being implemented for hydrogeology, geology, ‘mine’ planning and scheduling. These are generally off-the-shelf packages derived for other mining industries (Van der Riet, 2009). At Majuba the link between the wells can be established by pumping down very high pressure water, and forcing a path through cracks and cleats in the coal to the production well, at which stage muddy filthy water is pumped through the seam via an irregular path. At the same time, there will be an area around the injection well, roughly circular where the high pressure water will have penetrated before it found the route back to the surface via the production well. This is illustrated in Figures 6a and b.

When the gasification reaction has been started, the chamber is held at lower pressure than the surrounding hydrostatic head, so that water flows into the chamber and forms a seal which prevents gas escape, and part of the art in operating a reactor cavity is to keep the pressure at the right level. The gases coming out of the well will contain tars and particulates (ash and hydrocarbons), and will need cleaning. While the gas is currently simply being flared, both liquids and particulates are removed first.

One of the difficult things to achieve is the seal(s) around the well casings. The wells will be steel cased from the surface down to the coal seam and to establish a seal between the steel casing and the well walls themselves, wet concrete will be poured down the casing and forced up the outside annulus. When the concrete has set, the remnants in the casing are drilled out to facilitate a sealed connection between the surface and the coal seam. In relation to the well configuration, the further apart the better. This effectively increases recovery per well, and therefore decreases costs. Economics determine the optimal spacing, which will be different for each potential UCG location, dependent on geology, seam depth and thickness as well as other factors (Van der Riet, 2009).

5.15.2 Sasol pilot trial at Secunda Sasol recently decided to investigate UCG as a method of producing syngas for its CTL processes, from otherwise stranded coal. The pilot and demonstration facility is being developed as close as possible to the main Secunda complex. The site selected is about 0.5 km east of the main factory and contains approximately 2 Mt of coal in a seam which is about 3 m thick and 160 m deep. The coal properties in the area, on an air dried basis, are: G moisture 4.5% G ash 22.2% G volatiles 22.0% G fixed carbon 50.8%

In the longer term there is potentially some 30 Mt of coal in eight other nearby sites close to the Secunda complex. Their relatively close proximity would greatly assist the supply of utilities such as oxygen, steam and electricity, thereby lowering costs. The product syngas would be used as feedstock in the Fisher-Tropsch synthesis for liquid fuels production in the existing complex.

The current programme is as follows: G to commission the test facility in September 2009, and start the tests soon afterwards; G to end the operation of the test wells by mid 2010; G to start decommissioning and rehabilitation at the end of 2010.

The technology to be tested is the Linked Vertical Well (LVW) method, see Figure 24. The coal will be preheated and ignited using air and steam, and once the required temperatures are achieved, the main gasification will be carried out using oxygen and steam. This will produce a high heating value syngas, and the test will establish the CO:H2 ratio achievable.

The test programme has been carefully designed. There are three input parameters which can be controlled: G feed rate; G feed steam:oxygen ratio; G cavity pressure.

An important parameter which is difficult to control is water ingress. This is determined by a combination of cavity pressure, cavity size and overburden characteristics and possibly strata movement. To ensure that there is no gas leakage, the cavity pressure must be maintained at below the hydraulic pressure which is in turn determined by the level of the water table.

In contrast to normal laboratory experiments which are performed under controlled and measurable conditions, one UCG experiment may last for several days, and maybe even for several weeks, before firm conclusions can be drawn. The work at Secunda will be carried out to vary the input parameters in such a way as to minimise the number of experiments required using a well chosen statistical experimental design.

82 IEA Clean Coal Centre production wells injection wells

10 m directional drilling cavity 5

10 m directional drilling cavity 4

10 m directional drilling cavity 3 200 m

10 m directional drilling cavity 2

25 m 10 m directional drilling cavity 1

50 m 150 m

oxygen and steam syngas water level monitoring well top soil 3 m weathered dolerite 7 m water table dolerite sill 30 m

sandstone 120 m

coal ~ 160 m deep 3 m sandstone 80 m

Figure 24 Diagram of the Secunda UCG process showing the well matrix together with an elevation (Brand, 2008)

Underground coal gasification 83 In the tests, four pilot cavities will be commissioned using different process conditions to establish the optimum operating parameters for the UCG of Secunda coal. A fifth cavity will then be commissioned for a commercial-scale demonstration at the same site, and used to consume all the coal available to the pilot, including coal left by the preliminary experiments.

5.16 UK

The UK has large resources of indigenous coal both onshore, in and around the traditional mining areas, and offshore in the southern North Sea. Following the Spanish trial at El Tremedal in which the UK government was a participator, there was a significant level of government interest.

The Coal Authority initiated an investigation into UCG as a potential long-term energy exploitation option for the UK. This work was later taken up by the DTI. The situation is discussed in the Review of the feasibility of underground coal gasification in the UK (DTI, 2004). There is a parallel report which looks in detail at the UK resource entitled UK resource for new exploitation technologies (Jones and others, 2004). There were two additional reports, Review of environmental issues of underground gasification (Sury and others, 2004a) and a Best practice guide (Sury and others, 2004b).

The selection criteria used as an initial screening for possible development sites in the UK were: G depth between 600 and 1200 m (this was chosen in order to minimise any environmental impact from possible exploitation); G coal seam thickness >2 m; G the availability of good borehole data (from previous exploration); G keeping >500 m away from any abandoned mine workings and areas licensed for mining; G >100 m vertical separation from major aquifers.

Thus the UK is looking at generally deeper coal resources than developers in Australia and the USA, and probably coals of a higher rank. This is likely to involve a significant amount of development work. Figure 25 is a map showing the possibilities and prospects, and in particular the extent of the off-shore resources.

A number of target areas were identified in Yorkshire, Linconshire, Warwickshire and in the river Dee area with potentially suitable resources for UCG at a depth of below 600 m. There are smaller resources in South Wales and in the Clackmannan coalfield in Scotland. The Firth of Forth and the banks of the Dee estuary are particularly attractive because of their proximity to existing industrial sites. There are also massive resources under the North Sea with bituminous coal in multi-seam deposits down to well over 2000 m depth.

A detailed feasibility study was undertaken which identified a suitable site for a UCG trial. It confirmed both that geological conditions could be suitable for large-scale UCG exploitation and that because of impervious igneous structures, the contamination of groundwaters is unlikely. Development would use directional drilling and the CRIP configuration for controlling the gasification underground. It looked at possible areas at Kincardine, Grangemouth and Musselburgh.

The outcome of the study is of interest, because the search for a site became a greater challenge than was initially expected. Kincardine was soon ruled out because the river narrows to the west of Kincardine Bridge and any UCG operation beyond the initial trial would require the inclusion of onshore resources, parts of which are licensed for CBM extraction.

Grangemouth was more promising as the river is unusually wide and the surface banks already have significant industrial activity. However, the previous work had found that the Longannet-Grangemouth area had an unacceptable geological risk. Some structurally benign areas can be found within the prospect for trial purposes, but large areas are likely to be affected by structural and igneous features which would probably eliminate a commercial-scale operation.

As the study progressed, the coal seam area of Musselburgh to the west of Edinburgh was found to be superior on geological and hydrogeological grounds and the best geological option for large-scale UCG production. However, the parallel environmental impact study showed that surface constraints at the shoreline would make access and shore facilities difficult to locate, and any UCG operation would need to be based entirely on offshore platforms. For the other sites, there were more options for the location of shore-based plant, but the geology was less certain, and more data were required to prove whether any of the sites would be suitable for a UCG trial (DTI, 2006).

British Coal Gasification (BCG) Energy Ltd is a company set up in the UK to exploit UCG technology, including, in the longer term, the gasification of the very substantial coal resources under the North Sea. Any operations would be carried out in conjunction with CCS as described in their submission to the Scottish government (BCG, 2008). Early in 2009 the BCG subsidiary Thornton New Energy Ltd was awarded the first UK Coal Authority licence to win coal by using UCG. (BCG, 2009a,b). The company

84 IEA Clean Coal Centre outcropping coal-bearing strata

concealed coal-bearing strata

lignite deposits

areas with good UCG potential

Figure 25 Map of UK prospect areas for UCG (DTI, 2004)

was set up by a group with a strong background in offshore oil and gas exploration and production, and intends to combine the latest directional drilling techniques in UCG activities to produce syngas primarily for power generation. At the time of writing the company was in discussion with both government and local stakeholders prior to making applications for planning permission around and under the Firth of Forth. The potential developments are described in Creating the coalmine of the 21st century. The feasibility of UCG under the Firth of Forth (DTI, 2006). In the licence granted, it says that the initial target horizons are unworked coal seams from 500 to 3500 m deep. It has been granted for an initial period of three years, and renewal will be subject to progress with the development of the project(s).

Research in the Cardiff School of Engineering, Wales, UK Following an exercise to identify which parts of the Welsh coalfields might be suitable for exploitation using UCG, further work was proposed (Turner and others, 2009), in particular: G to characterise the organic and inorganic contaminant inventory arising from laboratory-simulated

Underground coal gasification 85 UCG using coals of various rank and under varying gasification and pyrolysis conditions; G to investigate controls on the solubility and mobility of the generated contaminants in groundwater and supercritical CO2; G to combine these data with hydrogeochemical and geotechnical models to formulate an EIA framework that will enable a future UCG/CCS operation to comply with UK legislation.

These efforts are complemented by the contributions made by a number of UK universities, including: G Heriot-Watt in Edinburgh; G Keele; G Imperial College, London; G Newcastle.

5.17 USA

The USA has vast coal resources, much of which are not extractable by conventional means. The US DOE ran an extensive programme of UCG trials from 1973 to 1989 which is discussed in Section 4.3. Coals in Washington state, West Virginia and Wyoming were used for the main trials. A report on The urgency of sustainable coal from the National Coal Council included a substantial section on UCG (Nelson and others, 2008). This highlights the need for a substantial research programme to resolve outstanding technical issues which remain unexplored. These include the process engineering, subsurface process monitoring and control, and the associated risks and hazards, as well as synergies with carbon management. Carbon management is discussed further in Chapter 9.

Currently, two major projects are being assessed, one in Indiana and the other in Wyoming. There are extensive deposits of unmineable subbituminous coal in Wyoming, and much of the past test work has been carried out in the area. GasTech has set up a partnership with BP to pursue the possibilities of large- scale UCG. Purdue University is carrying out an assessment of the possibilities of UCG in Indiana.

The LLNL continues to provide a focus for UCG work in the US. In particular the LLNL is pursuing all aspects of modelling (discussed in Chapter 7), and the issues connected with ensuring that the CO2 formed during the UCG process is captured and stored (see Chapter 9).

5.17.1 Wyoming GasTech have a lease on an area of some 32,000 ha in Wyoming. It has a huge coal resource of more than 13 Gt in seams more than 150 m deep and over 10 m thick. The average seam thickness is 20 m, and there is estimated to be nearly 40 Mt/km2 of coal.

In terms of implementing the UCG project, GasTech has completed the site selection and characterisation, and the necessary exploration work. Currently the permitting for the pilot operation is ongoing, and is expected to take some 18–24 months. The pilot programme will then take another 6–12 months. Following successful completion, it is proposed to develop: G both air and oxygen-blown UCG modules; G a commercial 200–500 MWe IGCC power project; G a FT liquids project using the syngas (Morzenti, 2008).

CCS from these is probable, and potential sites for EOR using the CO2 have been identified.

The pilot operation objectives are to improve upon earlier US UCG trials and produce a stable, dependable gas composition and flow. It would be necessary to maintain strict environmental compliance, and the experience from the tests would provide cost and operating data for commercial operations. It is intended to operate for a year with three UCG modules.

It would appear that the timing of these plans may have been modified a little, as GasTech have sold some other leases to Linc Energy (see Section 5.1.1), although the deal has not been closed at the time of writing. GasTech intends to help Linc through the permitting and local logistical issues, and to be involved in the pilot work which needs to be completed on these different leases within a two year timeframe. In partnership with BP, GasTech intends to pursue its original programme of assessment and test work on the 32,000 ha lease area described above (Morzenti, 2009).

5.17.2 Indiana A detailed assessment of the potential for UCG in Indiana is being undertaken at Purdue University, Indianapolis (Bowen, 2008; Shafirovich and others, 2008a,b,c). This is being carried out for the Indiana Center for Coal Technology Research by the School of Chemical Engineering at Purdue University and the Indiana Geological Survey (IGS).

While the IGS has defined the criteria for underground mining reasonably well, the criteria for UCG are

86 IEA Clean Coal Centre different, and some of the information in the literature is contradictory. The locations where UCG might be applicable will need information on the: G coal heating value (and its ash and water contents); G concentrations of sulphur, mercury and other contaminants; G feasibility of using the UCG cavities for CO2 storage, and/or the availability of other sites nearby; G product transportation issues; G environmental risks including possible groundwater contamination and uncontrolled combustion.

5.18 Vietnam

Linc Energy and Marubeni Corporation are reported to have completed negotiations with the Vietnam National Coal Mineral Industries Group (Vinacomin) to undertake stage 1 of the Tonkin UCG project in the Red River delta (Ecplaza, 2009; ABNnewswire (2009b). Stage 1 of such a project would involve the setting up and testing of some pilot wells in the area for the proposed development. This is the essential first step before a costed feasibility study can be undertaken with any confidence. The site is reported to be some 60 km southeast of Hanoi in Hung Yen province (Linc, 2008c). Other organisations in Vietnam may participate in UCG development, but there are no firm plans as yet. A recent report said that the Russian company Gazprom has signed an agreement to supply its UCG technology to Vietnam’s Dong Duong Co (VNBusinessNews, 2009).

In a report on CBM resources and their possible exploitation the coal deposits in the Red River basin are described as lying between 250 and 1200 m deep and spread over an area of some 3500 km2. The average coal thickness is quoted to be over 100 m (presumably the cumulative thickness of several seams) while the resource is estimated to be about 210 Gt. It said to be a subbituminous B coal, differing markedly from the anthracite in the Quang Yen basin (Do, 2008), but probably more suited to UCG, if the underlying geology is favourable. The Quang Yen coal basin has a potential resource of 5 Gt of coal under an area covering some 5,000 km2.

5.19 Discussion and summary

UCG is currently being assessed and tested with a view to commercial development in what are probably the most favourable circumstances, in fairly thick seams (5–20 m) and between 150 and 500 m deep. An appropriate geological/hydrogeological setting is vital, and the land on the surface needs to be largely clear of development. It should be emphasised that none of the projects has yet operated multiple panels for any period of time, which is the next stage of development. It will be several years before any of the operations will have reached this stage with the potential for becoming commercially viable and establishing that large-scale operations can be carried out without any significant deleterious environmental impact.

UCG is currently being assessed and tested with a view to commercial development in what are probably the most favourable circumstances, in fairly thick seams (5–20 m) which are only gently dipping and between 150 and 400 m deep. One pilot (in Alberta, Canada) is at a depth of 1400 m. An appropriate geological/hydrogeological setting is vital, and the land on the surface needs to be largely clear of development. It should be emphasised that none of the projects has yet operated multiple panels for any period of time, which is the next stage of development. It will be several years before any of the operations will have reached this stage with the potential for becoming commercially viable, and establishing that large-scale operations can be carried out without any significant deleterious environmental impact.

At present there are no broadly accepted standards for the siting and operation of UCG projects and facilities (Nelson and others, 2008). Different and sometimes contradictory criteria are to be found in the literature. Developers in different coals in different settings will need to follow the steps outlined in Chapter 4, of exploration, geological and hydrogeological assessment, pilot testing with one coal panel, followed by the operation of several parallel panels for a small turbine or pilot liquids production unit. Then carrying out feasibility studies and the design and costing of a commercial-scale operation, and finally construction. A careful assessment of the geological setting will be essential, together with the necessary permitting before each stage.

Walker (2008) summarises the amounts of coal gasified and the relative costs, comparing them with the recent test at Chinchilla, Queensland, Australia which is discussed in Section 5.1.1. Coal gasified in trials and operations since the 1950s: G in the USSR, and subsequently in countries of the FSU, over 15 Mt of coal has been gasified at an estimated cost of US$10 billion; G in the USA some 50,000 t of coal has been gasified since the 1970s at an estimated cost of US$300 million; G in Europe, less than 10,000 t of coal has been gasified at an estimated cost of US$100 million;

Underground coal gasification 87 G at Chinchilla, over 32,000t coal was gasified between 2000 and 2002 at an estimated cost of US$5 million.

To put the Chinchilla number (and the others) in a context which is more familiar to those accustomed to using coal for power generation, the amount of coal consumed during the two year UCG trial which was regarded as being wholly successful, would keep a conventional sub-critical 500 MWe boiler going for about a week. For the latest ultrasupercritical boiler it could keep a 600–650 MWe boiler fuelled for a week’s operation, and the comparison simply makes the point that the scale of the UCG activity to date has been quite small. All the tests in Europe, for example, have gasified <10,000 t of coal over a period approaching 50 years.

There is, however, a lot of experience to build on, even though many of the tests and trials have been relatively small scale and many have lasted for quite short periods. Many have also been carried out in shallow coal seams where the environmental risks have been relatively high. The best that one can reasonably say is that UCG has reached the ‘proof of concept’ stage but it is not yet a ‘proven’ process as has been claimed by some protagonists.

There are plans in a wide range of countries to investigate and assess the possible use of UCG to exploit unmineable coal resources. These need to be pursued in a measured and step-wise fashion, as is currently being done in both Australia and South Africa. The plans for developing UCG in India seem to be taking a similar measured path, at a sensible speed. It is the author’s view that if there were more openness and willingness on the part of all the developers to share their experiences, the technology would have a greater chance of successful large-scale development.

5.19.1 Factors affecting the control of the reactor The primary factors affecting the behaviour of the underground reactor are: G the nature of the coal seam and of the surrounding geological formations; G the flow rate of the injectant gases and resultant flows of the product gases in the cavity and in the linking passages; G the temperatures generated, and their stability; G the operating pressure, commonly maintained at a level just below the prevailing hydrostatic pressure; G the leakage of water into the reactor chamber, which will be affected by the quantity of water surrounding the seam as well as the operating pressure. Water intrusion can result in reducing the heating value of the product gas; G heat loss into the surroundings; G roof collapse; G the movement of liquids to the bottom of the seam.

Most of these provide the background for the discussion of geological and environmental issues in Chapter 6 and of modelling in Chapter 7.

5.19.2 The use of laboratory simulations A number of investigators have used laboratory equipment to simulate underground gasification conditions in an attempt to help to understand many of the basic mechanisms an to provide tools which will help interpret the results from pilot and demonstration-scale trials. Others have taken the view that the most effective way of understanding the mechanisms is a combination of pilot testing and modelling.

Among the organisations making use of laboratory simulations to back up observations from test work, and to contribute to UCG design are: G the China University of Mining and Technology, Xuzhou (Yang, 2003; Liu, 2003); G the University of Košice, Slovak Republic (Kostúr and Blištanová, 2009).

Much of the work at the CUMT has been to support the Chinese effort to recover energy from man-made mining galleries and tunnels, sometimes in mines which have otherwise been abandoned. The behaviour of lignite, of lean coal (probably with low volatiles) and of fat coal (probably with caking properties) was studied, together with the heat effects on both roof and bottom rock.

The laboratory generator used at Košice, in Slovakia, uses a tilting block which can therefore simulate the effects of coal seam dip/inclination. Coal from the Cíge² mine in the upper Nitra coal basin was used for tests. The effect of various process parameters on the combustion front was investigated, and the opportunity will be taken to compare actual channel propagation compared with that predicted by modelling.

5.19.3 Resource utilisation efficiency Most of the Soviet-era UCG operations discussed in Chapter 4 produced a fuel gas which was used as a

88 IEA Clean Coal Centre Table 8 Comparison of the resource utilisation efficiency of conventional mining and use with UCG (modified from Beath, 2006)

Conventional underground mining UCG

10% or more of the energy in the coal can be left mining and transport can use approximately 5% of the coal underground in the form of various wastes and partially energy reacted material

of the 1 MWh in the mined coal, 250 kWh are lost in the coal of the 900 kWh of energy in the product gas, 135 kWh are wastes (associated with coal preparation) lost in liquid wastes

from the remaining 750 kWh used for power generation, of the remaining 765 kWh of energy 380 kWh is lost in waste 415 kWh are lost in waste heat and 335 kWh of electricity heat and 385 kWh of electricity is generated are produced

The numbers are based around the use of 1 MWh (1 nominal unit) of mined/consumed coal and are simply indicative of the proportions involved.

supplementary fuel in a coal-fired boiler. Many of the past Chinese UCG operations have produced a fuel gas for domestic use, although some has been used for hydrogen production and some to produce ammonia (Beath, 2006). Utilisation efficiency is thus a question of both the amount of coal which is recovered from a resource, and the usability of the product syngas for particular applications.

In an assessment of utilisation efficiency, a comparison can be made between conventional mining and UCG as shown in Table 8. The comparison is made based on the use of the energy for power generation and on the use of 1 MWh (equivalent) of coal.

Since UCG would normally be used for otherwise unmineable coal the comparison is slightly unrealistic, but it is instructive in illustrating some fundamental differences. As UCG becomes more widely used, it will be helpful to develop realistic methods for assessing the resource utilisation efficiency. In the early stages, establishing practical and economic methods for syngas production in particular coal deposits while containing any environmental impact, will be the main goal. It will be useful, however, to develop ways of assessing resource utilisation efficiencies.

The UCG product syngas will have a different composition from every site, and will be significantly different from that from conventional surface gasifiers. For power generation applications, this has an impact on the design of the combustor and turbine to be used. The turbine is commonly specified based on the mass flow involved, so the gas compostion can have a significant impact.

A simple option for using the heat, as will initially be used at Majuba in South Africa is to use the UCG syngas in existing coal-fired boiler plants. This will typically be limited to about 30% of the energy input, but allows for very variable gas compositions (Beath, 2006). Modern gas turbines can use an UCG syngas with a range of compositions, but the efficiency of operation will vary.

UCG is a potential low cost option for providing gas for Fischer-Tropsch synthesis for producing liquid transport fuels. However the gas specification for this process is much more stringent than that for electricity generation, and long-term demonstrations are needed to establish whether and how this might be achieved. It may well be done by blending the gas from several parallel UCG reactors/coal panels, but this will introduce additional environmental challenges simply because of the scale of production. On any sizeable site, the syngas produced may lend itself (after cleaning) to the production of both power and liquid chemicals/fuels.

Underground coal gasification 89 6 Geological and environmental impacts

The development of an UCG prospect will depend, ultimately, on whether a viable commercial-scale operation can be established. The key elements include both the process performance, and broader social perceptions of the operation (Mallett and Beath, 2007). These will be affected by geological and environmental factors, which are principally: G site selection issues; G surface and groundwater impacts; G UCG reactor design; G its behaviour, and the prediction of this behaviour, for which appropriate guidelines need to be developed.

Extracting the energy from underground coal using UCG can result in less environmental impact than coal extraction by conventional mining and surface gasification. This is because of the elimination of surface impacts such as: G those due to open pit workings or the operation of winding gear for deep mines; G no coal is stocked or handled on the surface; G there is no coal preparation plant (with its demand for water); G there is no waste tip, and no dust.

An UCG site will have a collection of pipe manifolds which will be at a low level, and will need a control room, gas purification plant (to deal with tars and phenols, to remove sulphur and other impurities, and to separate CO2). During the life of the plant the pipe manifolds will cover a substantial area (equivalent generally to the area of the coal seam being used). The manifolds will cover parts of the area sequentially as various parts of the deposit are utilised and depleted.

It will also either export the syngas or use it on-site in an IGCC power plant and/or for liquids production for transport fuels and/or chemicals. Because the energy content of the syngas is in the region of 5 to 15 MJ/m3 (compared with natural gas which is ~40 MJ/m3) there is a strong incentive to use it on or near the production site.

The site will require road access for deliveries, possibly including substantial plant items, and it will almost certainly require a connection to the power supply grid. It will also require a wastewater treatment facility.

UCG may well result in some surface subsidence, as does underground mining. Surface structures would need to be protected by siting them where there will be no subsidence or by leaving a pillar of coal underneath.

The principal potential problem with UCG is the leakage of gases into the strata above the seam and the contamination of ground waters. With the right geology and with careful monitoring and control of the operating conditions (of the parameters such as gas flow and pressure, which are both measurable and controllable) the risks to ground waters can be eliminated or minimised.

To remove the stigma that UCG has had, particularly in the USA, as a particularly environmentally damaging technology, future demonstrations will need to operate without creating significant environmental impacts. Since previous UCG projects in the USA in the 1970s and 80s, a great deal has been learned about the behaviour and types of contaminant compounds produced by UCG and improved modelling can help to predict behaviour within the complex geochemical-geomechanical- geohydrological framework in which UCG operates. The worldwide UCG experience demonstrates that avoidance of environmental contamination in future operations can potentially be achieved by involving the integration of criteria for site selection with the choice of operating parameters (Burton and others, 2006).

Some of the steps that can be taken to avoid the situations that caused past groundwater pollution problems include: G ensuring UCG sites are situated where geologic seals sufficiently isolate the burn zone from surrounding strata; G selecting sites with favourable hydrogeology to minimise the movement of any contaminated groundwater flow; G isolating UCG locations from current or future groundwater resources; G balancing operating conditions to minimise outward transport of contamination from over- pressurised burn zones; G removing liquid accumulations of undissolved pyrolysis products at the end of the operation.

The environmental issues involved in UCG development are reviewed by Sury and others (2004a). This highlights the differences between the implications in the UK where UCG is likely to be used in deeper

90 IEA Clean Coal Centre seams compared with many other places where shallower seams may be exploited.

6.1 Exploration requirements

Geological exploration is costly, but essential. Inadequate exploration can prove to be even more costly. The amount needed will depend on the quantity and quality of any existing data, and the complexity of the geology both in terms of the rock structure, its stratigraphy and the presence of aquifers (Creedy and others, 2001). The hydrogeology of a potential UCG prospect is critical. Minor inflows of water into the reactor cavity can be accommodated by adjusting the injected water input. Larger flows of water could reduce the gasification efficiency because of the cooling effect, and a major inrush could even quench the gasification altogether. In addition, if any of the groundwaters might be used as potable water, the requirements for environmental protection are likely to be stringent. In relation to exploitation using UCG, both the consistency and inclination of the coal seam are important.

Geological data are not always easy to interpret, and boreholes may miss relevant and important features. Geophysical techniques such as seismic data collection can be used to reduce the geological risks and to minimise the uncertainties. Mapping techniques make use of the power now available in large computers which can facilitate quite elegant 3D projections of the spatial arrangement of geological structures many hundreds of metres underground. If the exploration is not sufficiently thorough and/or the mapping inadequate, then there may be unexpected drilling problems, delays, gas losses and cost increases. In a worst-case scenario the UCG prospect might even have to be abandoned. The geological risks would be higher in some formations than in others.

After the selection of a geologically appropriate site, the biggest challenges to be met are related to: G linking the injection and production wells in a predictable and controllable way; G controlling and containing the gas flows underground and controlling the development of the chamber in which the reactions take place; G monitoring and measuring what is going on so that appropriate action can be taken before any problems are encountered.

The underground reaction chamber will be of a somewhat irregular shape. It will move through the coal seam, and as the thermal distortions affect the surrounding rock, some of that may collapse, opening up new permeable paths. An important variable, dependent on the proximity of underground aquifers, is likely to be the influx of water, with the associated risk of groundwater contamination either directly, or by gases permeating through the surrounding strata. The gasification products include materials such as tars and phenols as well as hydrogen, methane and carbon monoxide.

In order to maintain the flows, the wells which are drilled from the surface are normally lined and sealed, while within the seam various strategies are used to control the point of ignition and the rate of burning.

UCG depends on the permeability of the coal seam to allow the passage of the reactant gases and, separately, of the products. This permeability nearly always needs enhancing, using the methods described in Chapter 3.

6.2 Site selection constraints

Because of the lack of reliable and comprehensive data covering a range of coals at different depths and in different geological settings, it is difficult to define firm guidelines relating to where UCG might be developed.

Virtually all the published site selection guidelines are based on the deposits in a particular area and apply only to a particular range of coals, seam depth and of geological conditions. Since this qualification is commonly left unsaid, much of the published literature is misleading, and the criteria listed are more accurately described as a preliminary screening for sites worth further consideration and investigation.

There are widely differing views between those making plans in Australia and others making plans in Europe. For example, the requirement to operate the UCG cavity at just below the prevailing hydrostatic pressure and having a water seal to prevent gas leakage may relate mainly to shallower deposits. In Europe where deep deposits may be exploited a depths between 500 and 1500 m, a water seal may not be relevant if there is an impervious rock formation above the UCG cavities (Kempka, 2009). The conflicting approaches relating to the possible need for a water seal compared with the need for a cap rock involve some gross oversimplifications of the nature of UCG. It seems likely that each UCG site will be unique, with shallow some sites having nearby water, and others being bone dry. Similarly some deep sites may be dry while others will have surrounding and overlying aquifers (Van der Riet, 2009).

Underground coal gasification 91 Likewise the suitability of the cap rock for providing long-term seal can only be determined by a detailed rock engineering study including an assessment of the effects of UCG where temperatures in the coal seam cavities may reach well over 1000ºC.

The main areas of concern for potential large-scale UCG operations are: G subsidence; G groundwater depletion; G groundwater contamination (Mallett and Beath, 2007).

Other environmental issues like wastewater handling and the necessary surface installations can be dealt with using conventional equipment and well proven procedures. The overall impacts of UCG in and above the seam are illustrated in Figure 3.

UCG like any other coal extraction technique will cause some subsidence. Its magnitude will depend on the seam thickness, depth, site geotechnical properties and the operational design of the gasification process in terms of how much coal is removed. The impact of any subsidence on site selection will depend on the use of the surface land lying over the deposit (Mallett and Beath, 2007).

No trials have been conducted in very thick seams, such as the brown coals/lignites in Victoria, Australia, or the brown coal in Slovenia (see Section 5.10). Similarly there was only one early test (in 1981) in a seam over 1000 m deep, and much more work would need to be done to commercialise energy recovery by UCG in deeper thicker seams, where there are almost certainly massive coal resources to exploit. The current pilot in Alberta, Canada at a depth of 1400 m is discussed in Section 5.3.

As the seam depth increases, drilling costs will increase, and so will the cavity operating pressure and this may make controlling the inflow of water more difficult. Both factors will affect the composition of the syngas produced. Water contamination at greater depths may be less of an issue since the aquifers there will almost certainly be saline.

Applying UCG techniques to thicker seams could offer a proportionately higher potential resource for recovery per unit of surface area which might translate into lower costs per unit of coal gasified. However it may be more difficult to control where the reactor cavity develops, and there are likely to be more problems and possible gas leakage as the strata above collapses and there will be significant surface subsidence.

At a recent course at Imperial College, London, UK run by the UCG Partnership (UCGp), one of the subjects discussed was ‘site selection’. Some historic guidelines were presented, see Table 9, but it was clear that there are as yet, no agreed, useful and widely applicable criteria. The criteria listed are very general, and do not take the geological setting sufficiently into account as it is quite difficult to describe succinctly. It seems that nearly all the site selection criteria published by various authors would be more accurately described as being ‘a preliminary screening exercise to eliminate obviously unsuitable sites’. The criteria also apply only to the coals which occur in the coalfields which the authors are discussing (ie their own local coalfields with which they are familiar). While the screening is a necessary and useful exercise, once the outline criteria are satisfied, the local geology and hydrogeology need to be looked at in considerably more detail.

Questions to be asked when possible UCG sites are being screened: G What is the nature of the coal deposit being considered, and how much is known about it? G How much exploration data (from boreholes and seismic) are already available? What further information will be needed? G What is the coal seam depth, thickness and inclination? G What is the coal rank, ash content and sulphur content? G How much coal is potentially exploitable? G What is the current use of the land above the deposit where UCG wells might be drilled and a project developed? Is subsidence likely to cause any problems? G What is the local hydrogeology and probable interaction between UCG reactors and the aquifers? Are any of the aquifers carrying potable water? Is there sufficient water to provide a seal for the UCG reactor cavities in a commercial-scale operation? G What is the nature of the rock above the deposit, and how permeable is it? Does it provide a gas- tight cap over the UCG reactors preventing syngas leakage? What is its permeability and does it have a structure which encourages even caving? G Is the area suitable for 3D seismic investigation?

Certain key questions relate to the local hydrogeology. If there is groundwater depletion (due to the use of water in the reactor) then this might result in a supply shortage for other users. The supply/inflow of water to the reactor affects the product gas composition and if the reactor pressure is reduced then there will be changes in the product syngas. The amount of depletion will be impacted by the proposed plant size (Mallett and Beath, 2007).

92 IEA Clean Coal Centre Table 9 UCG site selection criteria

National Coal Board, UK, 1976 (Korre and Durucan, 2008)

5 Mt of coal resource to provide 20 years of operation

not marked for conventional mining

not adjacent to working mines

removal will not cause unacceptable subsidence

seam thickness at least one metre or banded seam totals over a metre

ash content less than 60% including any dirt bands, as combustion may be impeded

area free of excessive faulting additional notes say that leakage may be excessive if the site is adjacent to old mine workings or in a faulted area, and that the impact of faulting and of the roof material on operation is largely unknown.

US criteria (Korre and Durucan, 2008)

minimum coal resource of 3.5 Mt and minimum overburden of 100 m (ie seam depth)

seam thickness >1 m, or 0.6 m in steeply dipping seams avoid seams with variable thickness and variable partings. Also avoid seams with overlying coal within 15 minimum distances – 1.6 km from populated areas – 0.8 km from major faults – 1.6 km from major oil and gas recovery development – 0.4 km from major roads and rail lines – 1.6 km from rivers and lakes – 3.2 km from active mines, and 1.8 km from abandoned mines

steeply dipping seams (>30º) are favoured because of lack of mining interest, and roof and floor conditions need to be examined

Australia CSIRO criteria (modified from Beath, 2006)

coal resource size suitable for long-term operation

seam thickness >5 m with a dip of <20º

seam depth 200–400 m with minimum faulting and no dips/sills

roof thermally stable with minimal permeability, preferably structured to encourage even caving

adjacent aquifers contain poor quality water and are of minimal permeability subsidence must be acceptable, and there should be few other human activities in the vicinity. There should be no overlying waterways., Purdue University criteria for Indiana coals (Shafirovich and others, 2008a,b,c)

seam thickness >2 m, suitability high; 1.5–2.0 m suitability medium; <1.5 m suitability low

depth >200 m

low rank, high volatile, non-caking bituminous coals preferred

shallow dipping seams are preferable

seams with no overlying aquifers within a distance of 25 times the seam height.

Cardiff University criteria (Turner and others, 2009)

coal seam thickness >1.5 m;

seam depth >500 m;

coal rank

proximity to fault structures >200 m;

proximity to built up areas >500 m;

proximity to mines both active and historic >500 m vertical and horizontal.

Underground coal gasification 93 The other major hydrogeological aspect associated with UCG is the possibility of groundwater contamination. This should be capable of being avoided completely by appropriate site selection and the use of correct operating procedures. Its impact can be most readily reduced by avoiding potable water aquifers altogether, but this may mean that development is restricted to deep seams. The other actions which will reduce the risk of contamination are to operate the reactor at below the hydrostatic pressure and to ensure that there is a low permeability strata above the coal seam.

At this stage, and probably for the next few years, it would seem sensible to develop the technology to commercial scale in contexts where the conditions are thought to be particularly favourable, as outlined in the CSIRO criteria listed in Table 9 which apply to large quantities of coal in the Surat Basin in Queensland, Australia, but not necessarily to coals elsewhere. Later development could tackle more challenging situations when there is a wider body of experience on which to build.

All the criteria are based around: G establishing that the coal resource is of an adequate size for economic development; G that the geological conditions are suitable for consistent coal removal; G acceptable environmental impacts (Mallett and Beath, 2007).

Two recent screening exercises which have been well reported are those carried out by Purdue University in Indiana, USA, and that by Cardiff University in Wales, UK (Shafirovich and others, 2009: Turner and others, 2009). It is interesting to note the different criteria applied in the two different situations see Table 9.

6.2.1 Geological and hydrological assessments The correct assessment of site geology is key to assuring that future UCG operations are sited to create minimal environmental risk (Burton and others, 2006). While there are numerous locations where coal resources are potentially appropriate for UCG, deep coal beds which are geologically isolated are especially attractive sites for future UCG operations. Suitable future UCG locations should be located at depths where local aquifers consist of saline, nonpotable water, with stratigraphic seals, with structural integrity, including no possibility of cavity roof caving that would create connectivity with other adjacent potable aquifers.

One key consideration which may determine whether an UCG prospect is considered to be viable is whether there is existing geological data of sufficient quality. Using the example of the Firth of Forth in Scotland, UK, because there has been extensive deep mining activity in the area, there is a substantial amount of ‘legacy’ exploration data. This includes that from mine shafts, andexploration bore-hole core data which can be digitised and integrated to produce an accurate 3D model (Walters, 2009). It is important to characterise the tectonic relationships which would influence UCG planning. Fault definition is crucial for determining both well paths (which may extend for up to 1 km in the seam) and environmental impacts. There is also a legacy of 2D seismic data undertaken for oil and gas exploration. The need for additional exploration will be heavily dependent on both the quality and quantity of the existing data.

In conventional mining, the term applied to the part of the mine where the coal has been removed and the cavity left has more or less filled up with waste and overburden is called a goaf. In the USA it is called a gob. In UCG goafing is required in order to close up the excess cavity both to reduce heat loss to the surrounding strata and to channel the oxidant stream close to and into the area where gasification is taking place (Brand, 2008). The commentary in this section is largely based on the description of the UCG pilot study planned at Secunda by Sasol (see Section 5.11).

The goaf behaviour is primarily determined by the roof span above the cavity and its properties. The caving which takes place is an integral part of the UCG process, and is important in maintaining an efficient flow regime in the reactor. The following aspects have been identified: G regular goafing must occur to ensure that the oxidant injected into the chamber is forced along the coal surface to maintain the reactions; G goafing must be high enough to ensure that the broken rock and rubble has bulked to the extent that it is in contact with the un-failed/unbroken overburden, thus preventing gas leakage; G the goaf rubble must compress and flood with water to such an extent that the permeability of the goaf is an order of magnitude lower than that of the cavity; G cavity pressure must be maintained, as in shallow seams, goafing to the surface may cause undue pressure loss.

For the planned development by Sasol in South Africa, modelling and practical experience was used from their mining and rock engineers relating to longwall mining and pillar extraction. They established that in the particular circumstance and in the strata where the trial will take place: G the initial goaf will occur within the creation of approximately an 80 m unsupported roof span; G the goafing behaviour is determined by numerous factors such as the local rock mass characteristics, stresses and discontinuities;

94 IEA Clean Coal Centre G if the initial cavity is too small, the goaf is not high enough to ensure adequate bulking to fill the void.

Thus the rock engineers should ensure the following in connection with the ‘design’ of the geometry of the gasification cavity: G the initial goaf must occur as soon as possible; G the initial goafing must be high enough to ensure that adequate bulking has occurred to prevent gas loss through the rubble; G to prevent the entire overburden from breaking and failing – which can easily happen in shallow seams.

Table 10 shows the relationship between the seam height Table 10 Goaf heights (Brand, 2008) and the required height of the initial goaf to ensure the complete filling of the void above the goaf. The Minimum required goafing heights implication is that a wider span must be created in thicker seams to ensure failure to a higher horizon. This will seam height, m goafing height, m ensure that sufficient bulking of the immediate overburden 2 ±20 occurs to completely fill the void above the rubble.

3 ±30 In Figure 26 it can be seen that once the roof span exceeds 100 m goafing has progressed high enough to ensure that 4 ±40 the top of the goaf is in contact with the unfailed rock, and there is no void. The geometry of the borehole layout must 5 ±50 therefore ensure that the critical span (the minimum unsupported roof span) of 100 m is created. The wider the critical span, the less risk there is of a goaf ‘hang-up’. a) cavity span >10>100 00 m and height of the goaf isis Figure 26b shows a simplified section of the overburden at approximately 404 m. TopTop of the goaf is in contactcontac ct the proposed site for phase 1 of the Sasol pilot UCG plant with the upper uunfailed rock (see Section 5.11.2). It is intended that for phase 1 no subsidence will occur, and this is possible because of a 30 m thick layer in the overburden. In the particular context it has been calculated that to ensure that the dolerite remains intact the critical span must be limited to <133 m.

Since Sasol Mining have been managing these issues for many years in adjacent mines, ground stability issues and caving mechanisms are well understood and goafing can be predicted and managed. With the process of UCG, there will be changing geological and hydrogeological conditions arising from cavity formation and growth. Management of the collapse in the form of leaving pillars in situ, pre-blasting, or of inducing goaf by hydrostatic pressure may be required. The Sasol experience of mining in the area provides unique insights and information about the behaviour of the overburden when subjected to UCG, b) cavity span 100-200100 0-200 m and height of the goafgoaf nowno ow close and this is an advantage not necessarily available to other to 40 m. Goaf recompressedre ecompressed by overlying largelarge blocks. There is now a cavity at the base of the thickthick dolerite,do olerite, developers. approximately i l 909 m above b the h coal. l However, if collapse occurs that leads to a gas-filled permeable region above the seam that is significantly higher than the reaction zone and gasifier chamber, then the gasifier operating pressure needs to be dropped below the hydrostatic head at the top of the gas void to avoid massive gas loss. The condition shown in Figure 26 will hopefully only occur after shut-down (Beath, 2009).

Generally, UCG should be worked from the lowest point on the seam to be exploited (ie with the reaction proceeding upwards along any dip), and needs to be arranged so that gasification has proceeded far enough before significant collapse occurs, so the kind of problematic collapse is avoided (Beath, 2009). Figure 26 Goafing behaviour a) for a cavity larger than 100 m Hydrogeology b) for a cavity small enough not to The UCG process has the potential to cause significant break the dolerite sill on the surface hydrologic and geomechanical changes in the area (Brand, 2008) surrounding the coal seam. Estimation of the

Underground coal gasification 95 environmental threat posed to groundwater resources as a result of UCG involves consideration of several elements, including: G the generation of contaminants within the burn chamber; G enhanced vertical hydraulic conductivity of the rock matrix above the burn chamber as a result of collapse and fracturing; G buoyancy-driven upward flow imparted by differences in fluid density reflecting different dissolved salt content distributions of groundwater in the vicinity of the burn chamber; G thermally-driven upward flow of groundwater resulting from in situ burning of coal; G whether speciation and partitioning of organic compounds, and possibly dissolved metals, will favour transport or sorption to mineral surfaces; G the potential for bioattenuation of contaminant compounds that migrate into potable water aquifers.

To address the issue of the environmental risk posed to groundwater, the parameters associated with these relevant processes need to be explored in order to identify, quantitatively, those scenarios which are most favourable for UCG and those which are least favourable. Output from such an effort will facilitate the comparison of risk scenarios (Burton and others, 2006).

6.3 Environmental impacts

UCG can be carried out with relatively little surface impact. There would be a network of relatively low level pipework which would be spread out over the whole area of coal to be extracted during the 20–25 year life of a commercial-scale project. At any one time, only a small part of the area would be host to active wells. Apart from the pipework and underground wells, there would be a syngas cleaning facility together with a power production unit (probably using IGCC) and/or a liquid fuels production plant. In the future, UCG might be used to produce hydrogen. There may be the need for an ASU or for oxygen storage, and possibly for a steam generator to provide the injection oxidant(s). There may need to be a storage facility for the chemicals and fuels required to promote ignition in new blocks of coal when they are brought on line. In addition to the plants and storages there would need to be an administrative block and laboratory facilities, and in remote areas it may even be necessary to provide some personnel living quarters. Appropriate wastewater treatment facilities would be a site requirement.

Compared with the conventional mining of coal and its combustion in boilers for power generation, UCG offers several advantages: G no SOx is produced, and the sulphur in the coal forms H2S and/or COS, both of which are relatively easily absorbed and converted into solid by-products; G no NOx is produced; G virtually all the ash remains underground in the reaction cavity; G roughly half the amount of particulates and of mercury reach the surface, and these can be dealt with by conventional methods (Friedmann, 2006).

The treatment plant and administrative buildings need to be built where there is no subsidence risk and therefore away from the area which will be exploited. As UCG will normally take place in relatively open countryside where it is possible to drill the wells over quite a wide area and to install the associated pipework, any subsidence which results will probably not be a major constraint on development.

The principal environmental concerns with UCG are connected with possible groundwater contamination, and with subsidence. The groundwater concerns are substantial, but in more than thirty trials in the USA, only a few resulted in contamination. Both Hoe Creek II and III, where there were problems, were carried out in what would now be regarded as high-risk areas. Both sites were in shallow seams, interbedded with highly permeable strata and with freshwater aquifers. There is an extensive report detailing the actions taken in connection with the remediation of the Hoe Creek site (US DOE, 1997). The Carbon County UCG also had significant problems, and some sites in Texas required some post-test clean-up (Beath, 2009).

It is said that none of the UCG activities in other countries, including the 46-year project at Angren in Uzbekistan, have resulted in contamination (Friedmann, 2006). However, some of these may not have been particularly carefully monitored and many only operated on a small scale for a short period. One Russian study at Podzemgas in the Kuznetsk basin where UCG was undertaken in a seam 300 m deep carried out monitoring of the subsurface waters for a period of three years. It was reported that a deep depression was created in the subsurface waters around the reactor space operating according to the traditional Soviet technology (by removing moisture with the syngas product and by pumping water from the gasification cavity). This localises the pollution and prevents its spread. As the water gets hot, it dissolves salts from the formations it comes into contact with. After gasification the subsurface water level returned to normal, although temperature anomalies lasted for quite a long time (Dvornikova and Kreinin, 1993). There is evidence that the gasifier operated at a pressure above the prevailing hydrostatic pressure and gas leakage of 7–15% was reported.

The recent Chinchilla, Bloodwood Creek and Majuba projects in Australia and South Africa respectively

96 IEA Clean Coal Centre have been carefully monitored with no reported evidence of groundwater contamination, although the scale of the activity is still very small. At Chinchilla there were 19 wells around the first pilot UCG burn to assess any groundwater changes. The next stage with both projects will be a significant extension of the land area involved as more segments of the deposit are gasified. The initial scale of the expansion will be initially approximately ten times while in the longer term, for a commercial-scale operation the expansion could be as much as a hundred times, involving very different patterns of water flow underground. The groundwaters will be thoroughly monitored and the information obtained will be of considerable importance in establishing the operating conditions under which contamination can be minimised. For assessing the future potential of UCG and the geological circumstances in which it can be used, more long-term tests are needed in different coal deposits and on a large scale.

6.4 Monitoring possibilities

As the reactor is underground monitoring UCG presents significant challenges. The only parameters that can be measured with certainty are the gas compositions, flows and their temperature in and out, together with the operational pressure. Some downhole instrumentation and gas sampling may be possible. It may be that surface seismic will facilitate following the progress of the underground reactor, but this would be costly. The LLNL has begun to simulate and test various monitoring tools to improve process control. It is hoped to validate some of these by 2010 possibly in combination with CCS monitoring (Friedmann, 2008). The methods include: G direct monitoring of pressure, temperature and flows, and of geochemical parameters; G looking at the use of tracers; G indirect monitoring using passive geophysics (for example microseismic work); G electrical surveys involving electrical resistance tomography.

6.4.1 Monitoring wells There is considerable sensitivity over the possibility of groundwater contamination from a UCG activity, partly arising from tests in the past where this happened. The reasons in each case were almost entirely associated with issues connected with poor site selection and inappropriate reactor operating conditions. With modern procedures for site selection, the operation of the reactor at a pressure which is below the hydrostatic pressure surrounding it, and with reactor sweep-through as part of the shut-down procedure, contamination is very unlikely.

Nonetheless, and particularly until there is much more operational experience with UCG, monitoring the site and the operation closely will be an ongoing necessity. At the recent pilot burns at Chinchilla and Bloodwood Creek, both in Australia, the reactor area was surrounded with a number of monitoring wells at various depths to check on pressures and flows, and to take water samples. The measuring points were located both above and below the reactor area, and alongside it.

Similarly at Majuba in South Africa (see Section 5.15.1) there has been extensive monitoring, using: G a range of baseline tests and analyses done prior to and UCG activities. These comprise flora and fauna audits, water analyses, ambient air tests, soil tests and noise audits; G successive perimeters of devices for measuring groundwater hydrostatic pressure, and its temperature which were installed before any UCG-related activities on-site, as were wells for withdrawing water samples from surrounding aquifers for routine analyses; G there are extensiometers installed for subsidence monitoring; G the syngas composition is monitored on-line (Van der Riet, 2009).

6.4.2 Managing ground deformation UCG reactor designs must provide consistent high volume syngas production, and will probably use a series of parallel panels. Commercial-scale UCG will remove similar volumes of coal to that from a longwall mine. It has not yet been tested on any scale in really thick coal seams (>20 m) where the implications of extraction will need further study and assessment.

As the coal is burned/gasified progressively, there will be cavity collapse which will result in both subsidence and, probably, increased water inflow. The collapse may well cause mixing in the overlying aquifers, together with some surface subsidence (see Figure 3).

Mallett (2006) suggests that large-scale shallow UCG extraction will open direct pathways from the gasification cavity to the surface. This could involve gas leakage, and increased water flow into the cavity, possibly disrupting the gasification. On this basis, the minimum depth for large-scale extraction should be 300 m so that a 150 m undeformed buffer can be maintained over the disrupted strata. Above 300 m depth only partial extraction by UCG is safe, which limits the syngas production rates achievable and the proportion of the coal that can be recovered.

A numerical modelling system that was developed by CSIRO for application around conventional

Underground coal gasification 97 mining activities has been adapted to apply to UCG operations. It is called Cosflow, and is a coupled dual porosity two phase flow model with a sophisticated finite element code. It can be applied to predict the effects of strata movements and vertical displacement on the groundwaters (and hence on water inflow to the cavity) and on surface subsidence.

A thorough understanding of the issues connected with ground deformation can ensure better information for site selection/rejection, and can contribute to managing the issues where development is pursued. It is necessary to thoroughly monitor what is happening on a UCG site, and to have a planned response to identified risks. This could include specific operating procedures to mitigate possible unwanted impacts.

6.5 Regulatory frameworks

In most countries, UCG activities would be subject to land use, planning and environmental regulation provisions. The principles are likely to be similar in different places, but in practice the coal/mineral resources in some countries are subject to special regulations covering their exploitation, and as UCG is poorly understood, it is not always clear whether UCG will be regarded as a mining operation (coal removal) or as an operation more like oil and gas recovery. There are likely to be existing regulations covering conventional mining, CBM recovery, together with oil and gas recovery, and the necessary exploration work needed for all these activities. All will have been drawn up before there was any thought given to the commercial development of UCG.

Just as an example of diversity, in the UK, land use planning provisions in England and Wales differ in some respects from those in Scotland, and significantly from those in Northern Ireland (DTI, 2004). Similarly there are differences in regulatory approaches between the various states in both Australia and the USA – and this illustrates one of the key hurdles that UCG projects have to overcome.

UK regulatory guidelines These are described in some detail since the principles applied are likely to be similar in other countries, and the following outline is drawn mainly from DTI (2004) which discussed the feasibility of UCG development in the UK.

UCG is covered onshore in the UK by land use, planning and environmental regulation provisions. There is currently no spatial planning system offshore, thus each proposal would be considered on its merits. However, any gas recovered offshore would be taken to storage and power generation or liquids production facilities onshore and these would fall within the ambit of planning provisions.

Development of a trial site for UCG, or of a full production facility, would be considered as a mining operation in any planning application. However, any associated electricity generation or liquids production facilities would be regarded as an industrial facility. Therefore, policies concerning both mining and industrial operations would need to be taken into account by the relevant local planning authority.

Under Town and Country Planning provisions, there is a presumption in favour of permitting planning applications, if environmentally acceptable, subject to suitable mitigation measures, where these are in conformity with policies in the minerals development plan. Since UCG is a recent issue in the UK there is an absence of specific policies concerning the extractive element of any proposal in development plans, and applications would be considered on their merits. However, there will be policies relevant to industrial facilities that are relevant to processing and generation facilities. If the local planning authority refuses an application, it may be the subject of an appeal to the Secretary of State.

Account needs to be taken of the EIA Regulations that apply to some forms of development. Since there is some uncertainty about the environmental impacts of UCG until a trial has been undertaken, it seems likely that a planning authority would require an EIA to be prepared in respect of any planning application. It would be wise to discuss this issue with the appropriate authorities at the earliest opportunity and determine, if appropriate, the scope of any Environmental Statement required.

Although extraction beneath the sea would not be within the scope of land use planning, it again seems likely that EIA would be required for similar reasons. Material information to the determination of a planning application may include, for example, impact on the local environment, population and habitats. In the case of UCG, many of the issues associated with the storage and processing facilities would be similar to those of a broad range of industrial facilities. In the case of the extractive operations, drilling and dealing with associated impacts would be broadly similar to other forms of hydrocarbon exploration and extraction. Particular issues associated with UCG would include, however, the extent to which the operation can be controlled, the adequacy of the procedures for closure, and the potential impacts and containment of contaminants especially with regard to underground and surface water. Some of these matters are also the subject of environmental regulation, and the planning conditions should complement, and not conflict with or duplicate, any licence conditions. Therefore, close liaison is required between

98 IEA Clean Coal Centre the applicant, the planning authority and the environmental regulator.

The UCG process, for both the trial and semi-commercial operation, would be covered by the Integrated Pollution Prevention and Control Regulations (IPPC) 2000. UCG, like all gasification processes, will need an IPPC permit from the relevant Environment Agency. IPPC requires the application and use of best available technology for all emissions and detailed technical guidance is available, with revisions in preparation.

Approval under the Groundwater Regulations 1998 is part of the IPPC permit process. Normally, the release of contaminants to groundwater is prohibited, but the Regulations allow exemptions for pollutants such as phenols and heavy metals (List I & List II substances) for permanently unsuitable groundwater provided the substances cannot reach other aquatic systems. The regulatory position at present is that UCG is likely to obtain groundwater consent if it can be established that: G adjacent groundwater can be declared permanently unsuitable; G the transfer of contaminants to upper aquifers will not take place; G shallower aquifers are protected from leakage from access boreholes.

In addition, a surface access agreement would be required from appropriate landowners.

It is currently uncertain as to whether a petroleum exploration and development licence (PEDL) would be required, in addition to any licence that the Coal Authority would issue for UCG. An existing PEDL holder may also have to be consulted. These anomalies of the UK licensing systems need to be addressed, and is an action proposed and requested in the DTI report (DTI, 2004).

The drilling and exploration boreholes and the subsequent injection and production wells would require from the Coal Authority: G an exploration licence; G an operational licence to work the coal; G a leasehold interest in the coal; G an access agreement, where necessary, to pass through other coal seams.

All safety matters related to the drilling and operation of underground boreholes and extraction of hydrocarbon gas from onshore sites are covered by the Offshore Safety Division (OSD) of the Health and Safety Executive and a memorandum of understanding has been drawn up between the Mines Inspectorate and the OSD.

Notifications are required under: G the Borehole Site and Operations Regulations 1995; G the Offshore Installations and Wells (Design and Construction) Regulations 1996.

These regulations specify the procedures required for the design, planning, operation, supervision and abandonment of the process, and require that an independent well examiner oversees the written well examination scheme and the safety documentation. A two-stage approval process is foreseen in which the project is divided into a construction, and an operational and abandonment phase. Approval of the UCG operations from a safety standpoint will require detailed consideration of the underground ignition, gasification and associated activities; significant effort will be required to develop and agree the necessary documentation with the OSD.

The above-ground plant for oxygen supply, gas clean-up and liquids production or power generation may be located some distance from the wellhead configuration and be connected by transmission pipelines. These will be subject to the normal safety regulations for industrial plant; namely, the Health and Safety at Work Act 1974 and COMAH 1999.

In other countries In view of the nature of UCG, India regards the activity as being similar to CBM recovery and to natural gas based operations, rather than to conventional coal mining. It therefore intends to develop UCG under the Petroleum and Natural Gas Rules, 1959, with a minor modification to the definition of ‘Petroleum’.

From the experience in the USA, it appears that the major regulatory issues and challenges associated with UCG are related to: G the possibility of groundwater contamination; G possible surface subsidence; G competition between different energy technologies for the same resources (Covell, 2007). This can particularly be with CBM recovery where regulations, procedures and rights and licences have already been set up. This issue has also been evident in Australia.

In the USA, various regulations which might impact UCG derive from Federal Authority, including the: G Mineral Leasing Act; G Safe Drinking Water Act (administered by the EPA);

Underground coal gasification 99 G Underground Injection Control Program (administered by the EPA); G Surface Mining Reclamation and Control Act; G National Environmental Policy Act for Federal Projects.

Since major UCG developments are under consideration in the state of Wyoming, the permitting requirements are relevant. Many of the trials in the USA in the 1970s and 80s took place in Wyoming. As a consequence, the state has in fact developed environmental regulations specific to in situ technologies (both UCG and in situ uranium mining). The surface regulations are the same as those for surface mining while subsurface there are a series of special rules and regulations.

One side issue in Wyoming is that UCG is regarded as ‘underground mining’. In the state, coal leases have 12½% royalty on the gross coal value if it is surface mined, and only 8% if it is underground mined. As the coal is not brought to surface the amount consumed/reacted will need to be calculated in order to calculate the necessary royalty payments (Morzenti, 2008).

The permitting procedure in Wyoming (Covell, 2007) involves: G preparing a mining/extraction plan with a process description and design, with the proposed layout, and detailing the arrangements for waste disposal and for groundwater and other monitoring; G preparing a reclamation plan with shut-down procedures, surface reclamation, groundwater restoration and a reclamation bond calculation; G presenting supportive information on a range of issues such as land use, archeology, hydrology and water rights, vegetation, wildlife, wetlands and alluvial valley floors (where relevant).

There will be different stages, and as a preliminary, there will need to be a R&D Testing Licence for the initial pilot trial, and then a Permit to Mine covering the area to be used for commercial development. The processes involved may well take some 18 to 24 months to complete, and involve a significant investment of both time and money during which there will be a degree of uncertainty about the outcome.

There will be particular issues in Wyoming, because an earlier UCG trial in the 1980s at Hoe Creek resulted in significant levels of groundwater contamination. However, this was almost entirely due to poor site selection, and a great deal has been learned about UCG since then, so that any similar contamination is now extremely unlikely. The real issues involve possible gas losses, the interconnection of the underground reactors, surface disruption and water influx. All can be tackled by careful site selection, operating at sufficient depth and by the design of the gasifier modules, together with control of the operating conditions.

There are no definitive regulations in Wyoming covering UCG and prioritising use of the coal resource for either conventional mining or for CBM recovery, since UCG is not yet a commercial activity. This is likely to be the situation in most other places where commercial development is under consideration.

100 IEA Clean Coal Centre 7 Modelling

Because the UCG process takes place out of sight, and with minimal instrumentation. It is difficult both to understand exactly what is happening underground, what the reaction conditions are and what effect they are having on the seam and strata. Modelling can potentially make a significant contribution to improving this understanding.

The American development effort in the 1970s and 80s was the first to use computer modelling to help with the understanding of the process. With the enormous increase in the power of computers in recent years, many more aspects of UCG can be modelled in greater detail. However, the only test of a model is when it is validated by experimental data from an operating site, possibly by drilling into the underground cavity and checking whether the predictions are borne out in practice. Currently very few models have been validated in this way, but as the operations in Australia and South Africa become more mature, this kind of validation needs to be undertaken.

Work on modelling UCG is ongoing in a number of places including Australia (at the University of Queensland and by both Carbon Energy and Linc Energy); in India (at IIT Madras); and in the UK and USA. Most published models are limited to an analysis of only a part of the process (Beath and Mallett, 2006).

There are many different kinds of models which can be used, including: G simple spreadsheets used to look at overall project parameters; G ASPEN and similar programmes, used mainly to look at surface facilities and their interaction; G fluid dynamic modelling relating to how cavities grow, and how UCG propagates – also to the variations in product gas composition; G structural modelling which includes subsidence in the strata around the cavities and its effects on the hydrology.

UCG is a complex process involving interaction between in situ coal (with variable properties) and the injectants (air or oxygen/steam) following sometimes unpredictable flow paths, as well as with the water that may flow into the cavity. Other processes go on in the gas phase as the products pass through the reactor cavity and their temperature changes. The surfaces of the reactor cavity are continuously being altered. Beath and Mallett (2006) highlight the need to address the interactions between: G geological factors; G the gasification process; G surface impacts and groundwater changes; G public perceptions.

Among other things, the models developed need to deal with: G design parameters such as coal seam depth, thickness and inclination. Coal properties, including kinetic parameters, permeability and strength. The well and reactor configuration – in addition to the hydrogeological and geomechanical characteristics of the site; G operating parameters such as the injectant composition, pressure, temperature and flow rate. Reactor conditions which may have to be deduced from the product gas characteristics such as its composition, pressure, temperature and flow rate; G performance parameters such as the resource recovery factor, product gas quantity per kg of coal, product gas per m3 of injectant gas and an assessment of process efficiency (Kolar, 2008).

The process involves fluid flows, heat and mass transfer, combustion and gasification with both heterogenous and homogeneous reactions, together with the thermal geo-mechanics of the coal and surrounding strata (Kolar, 2008). An integrated UCG simulation is shown in Figure 27 where both the underground models and a surface facilities model can be combined. Because of the difficulties involved in carrying out meaningful laboratory experiments on the surface and in obtaining ‘real’ data from underground cavities, process modelling can play an important role in helping operators to understand and visualise the complex underground processes taking place. All the underground models, however, require validation.

The integrated simulation includes: G a coal sub-model which predicts the coal behaviour during pyrolysis and both combustion and gasification. In view of the enormous variations in coal characteristics, different sub-models/codes are likely to emerge in different places; G a linking sub-model which estimates the linking time between the injection and production wells and the flame stability in the cavity. This will depend on the linking method used, and will be different for links made by hydrofracturing and reverse combustion and those arising from in-seam boreholes; G a reactor sub-model which needs to describe the behavioural characteristics of the coal, char and ash, in the reactor zone, and the development of temperature, pressure and gas compositions. It

Underground coal gasification 101 integrated UCG simulation

underground model surface facilities model (physical and mathematical) (component-wise energy and mass balance)

coal sub model ground subsidence (CSIRO) geo technical sub model (in-house code) software: TrapTester, Rockware, Petrel, GeoSec

ground water linking sub-model hydrology sub model (in-house code) software: MODFLOW, MT3D

UCG process sub models for processes in reactor sub model the facility (LLNL, CSIRO, Perkins (purification, CC Power Gen) software: FLUENT software: ASPEN PLUS (CFX, STAR-CD)

Figure 27 An integrated UCG simulation (Kolar, 2008)

needs to define the rate of cavity growth, its size and to be able to forecast the product gas characteristics; G a geotechnical sub-model to predict ground movement and subsidence, water influx (which may be heavily pressure dependent), and both gas and liquid flow into the affected strata over the UCG zone; G a regional hydrology sub-model which predicts large-scale hydrological behaviour around the site.

LLNL in the USA has been active in UCG for a long time. It developed cavity growth models and a computational fluid dynamics (CFD) based model of the process and integrated this with Aspen Plus. CSIRO in Australia have also developed cavity growth and gas production models.

Perkins (2005) has developed a series of models to predict the behaviour of UCG reactors from a number of different viewpoints, including: G the effect of operating conditions and coal properties on cavity growth; G combined transport phenomena and chemical reaction; G gas production in an UCG gasifier.

The rate of gas production, and its composition in an UCG reactor varies widely, depending on the oxidant used (air or oxygen/steam), operating conditions such as the gas injection rate and temperature, coal type and seam conditions, the operational pressure and the behaviour of the surrounding strata and of the water.

The modelling must deal with the three design concepts for UCG in: G vertical wells; G using a CRIP in-seam; G steeply dipping seams.

The output should provide information and advice for future operations on how to: G prevent excessive heat loss;

102 IEA Clean Coal Centre Table 11 Typical UCG models which have been developed (modified from Kolar, 2008)

Model Observations – a pear-shaped cavity would grow around the injection well, narrowing towards the Reactor sub-model production well (Wilks, 1983) – the model assumes that combustion and gasification reactions are uniformly distributed over the whole reactor height

Reactor sub-model at LLNL – 3D axisymmetric model to simulate CRIP experiments (CAVSIM, 1989) – applicable to non-swelling coals

– gasifier model based on thermodynamic equlibrium Two box sub-model – coal distillation and char combustion and gasification takes place in two separate (Dufaux and others, 1990) reactor zones

Reactor sub-model – 3D model to combine reactive heat and mass transport together with thermo- (Biezen and others, 1995) mechanical behaviour (developed at the Technical University of Delft, Netherlands)

– 2D model which includes coupling of the heat and mass transfer and chemical Reactor sub-model reactions occurring at the cavity boundary (Perkins and others, 2003)

Steep coal seam sub-model – mathematical models established for the temperature, pressure and concentration (Yang, 2004) fields

– predicts the operating regimes that are required for efficient gasification Coal sub-model – the output includes the variation of temperature, porosity and carbon conversion along (Beath and Mallett, 2006) the distance into the coal seam

Reactor sub-model – 1D model to investigate the effects of operating conditions and coal properties on the (Perkins and Sahajwalla, 2006) local rate of cavity growth and energy effectiveness

– 2D steady-state model with the ultimate objective of integrating with process simulation software such as Aspen Plus Reactor sub-model – LLNL have developed a CFD model for a cylindrically symetric cavity which considers (Upadhye and others, 2006) coal pyrolysis and the influx of water. The WGS reaction and coal gasification reactions are considered to be volumetric, but known kinetics are used

Reactor sub-model – 3D model of CRIP-type reactor to predict flow, cavity volume changes and product gas (Beath and Mallett, 2006) composition

Linking sub-model – 2D unsteady-state model assuming stability of the combustion front Blinderman and others (2008)

– a zone of high permeability between the wells leads the initial formation of a single Reactor sub-model channel, but ash clogging causes sideways and upward expansion of the channel (Biezen and others, 1995) – a low permeability ash layer forming at the cavity bottom leads to the bypassing of a considerable amount of coal – maintaining a higher temperature in a longer gasification channel promotes the stability Steep coal seam sub-model and heating value of the product gas (Yang, 2004) – increasing the gasification time increases the pressure drop in the gasification channel

– the characteristic shape of the cavity growth rate increases at low water influxes and declines as the water influx is increased Reactor sub-model – the cavity growth rate increases with increase in moisture content; and at a given (Perkins and others, 2006) temperature, with the volatile matter content of the coal – the build-up of an ash layer significantly reduces the cavity growth rate

– the linking time is proportional to the squared distance between the wells (in the absence of developing instabilities of the combustion front) Linking sub-model – the combustion temperature in FCL is significantly higher than in RCL (Blinderman and others, 2008) – the cavity formed in FCL has a pear shape, whereas in RCL it is a relatively narrow channel

Underground coal gasification 103 G prevent excessive gas loss; G prevent or minimise failure of both the injection and production wells; G minimise the environmental impact of the process; G manage the behaviour of the under- and over-burden, and its impact on both the process and the environment.

Modelling can provide the basis for: G identifying the key parameters for efficient design, smooth operation and performance enhancement; G predicting the overall performance of the process; G controlling the process to meet required objectives; G optimising the process under local conditions.

Some of the principal models which have been developed are listed in Table 11.

Australia (CSIRO) The CSIRO/Carbon Energy suite of models address most of the issues and are currently being validated and modified based on the results from Bloodwood Creek (see Section 9.1.2).

The coal model is based on the series of UCG reactions shown in Figure 4. It looks at the conditions in the wet coal, with an initial evaporation front; in a devolatalisation zone and finally in the gasification zone where the char reacts. The model addresses coal and char reactions, and structural changes; gas flows and reactions – and heat transfer. It can be used to predict the general operating regimes which are desirable for efficient gasification.

The cavity model looks at a similar list of factors, in conjunction with rock and coal breakage and collapse. It uses a 3D model of a CRIP-type reactor and includes chemical, heat transfer and flow processes. It can produce a process simulation for producing a syngas to feed a liquid fuel synthesis plant using Fischer-Tropsch, which is a tempting option due to the high value of the products.

COSFLOW is a related geotechnical model addressing issues such as ground deformation, water flow and gas losses. It was developed by CSIRO together with JCOAL and NEDO in Japan (Beath and others, 2007).

CSIRO say that the suite of models has been developed and demonstrated to provide predictions and a basis for decision making, relating to all the UCG processes taking place. What is now necessary is that the models are tested at specific sites to verify that the process and environmental performance is potentially acceptable. However, each site is unique, and so all the modelling must be repeated for each new location, and related to the proposed size of the prospect.

India (IIT) IIT have developed a reactor model where the gasification channel is assumed to be a packed bed in which: G there is a steady state in the gas phase; G the solid reactants, coal or char, are stationary; G the gas phase consists of eight species (N2, O2, H2O, H2, CH4. CO, CO2 and tar). Axial dispersion is not accounted for (Khadse and others, 2007a).

The pseudo steady-state model can be used to predict gas composition, temperature profiles and movement of the reaction zone. It can predict the effects of water inflow and of changes in the oxygen content of the injectant gas. However, the model is one dimensional and cannot predict the cavity size and shape. The present model is an important preliminary step to modelling the actual UCG process and 2D and 3D versions need to be developed.

USA (LLNL) The LLNL has access to powerful computers for UCG modelling. It has a Computational Fluid Dynamics (CFD) model in which a cylindrical cavity is assumed. It considers coal pyrolysis and water influx. The WGS reaction and coal gasification reactions are considered to be volumetric, and known kinetics are used. LLNL can also carry out simulations of the impacts of UCG on geologic and hydrologic systems (Upadhye and others, 2006). More of the LLNL work is described in Friedmann (2008).

China It is noteworthy that China has published relatively little about its modelling efforts, although there is likely to be ongoing work at the China University of Mining and Technology in Beijing. The lack of published information may be because much of their work to date has concentrated on steeply dipping coal seams, as described by Yang and others (2007).

104 IEA Clean Coal Centre 8 Syngas use

Since this report is focused on the underground and as yet largely unproven aspects of UCG, this chapter will include only a brief overview of the possibilities for syngas use. The first requirement is for an appropriate gas cleaning stage to remove tars, particulates and other unwanted contaminants.

Most of the syngas cleaning and usage processes are established and proven, although there may need to be some development work on turbine design for using a syngas fuel and on dealing with variable syngas composition during chemical and liquids production. Some aspects are discussed in more detail in another IEA Clean Coal Centre report Coal to liquids (Couch, 2008). The necessary developments will use fairly well established approaches and methods, and should be capable of technical solution.

The UCG operation can be optimised to produce either a fuel gas with the highest possible heating value, or to produce a high hydrogen content product for further synthesis (Beath, 2003). Typically a H2:CO ratio of 2:1 is optimal, but different processes have different requirements. The proportion of CH4 is not often discussed in the literature, but it should be noted that can contribute significantly to the heating value of the product syngas. As described earlier, the composition of the product gas (referred to here simply as syngas) is dependent on a range of factors, including, principally the composition of the injected feed gas, but also water influx, the temperatures through the reaction cavity, its pressure and the nature of the coal. It also depends on the ‘age’ of the particular reactor cavities.

The product gas from UCG can be used for a number of different applications, in particular for: G low grade heat generation for industrial size boilers or as a supplementary fuel in a boiler based on another fuel. Most of the syngas produced in the USSR was used in such applications; G power generation using a suitably designed gas turbine; G methanol or ammonia synthesis, depending on the syngas composition and its subsequent treatment; G producing liquid transport fuels using Fischer-Tropsch synthesis; G separation into methane and hydrogen streams for use as petrochemical or fertiliser production. The LLNL is promoting the possible production of hydrogen in conjunction with CCS (Friedmann, 2008).

The syngas specification for these applications and the consistency required will be very different. The most forgiving, which can cope most readily with product gas variations will be the low grade heat and power generation applications, particularly where it is used as a supplementary fuel. Most of the syngas generated so far has either been used for power or heat generation, or has been flared. The gas composition has not been a particularly sensitive parameter and use as a fuel allows for more variability than its use for chemical and/or liquid fuels production. Turbine design and development for air-based syngas is ongoing at Majuba, South Africa, and for oxygen-based syngas at Bloodwood Creek, Australia. Gas turbine technology for syngas in coal-based IGCC is discussed in another IEA Clean Coal Centre report (Smith, 2009).

The only coal-to-liquids (CTL) application is that at Chinchilla in Australia where pilot plant work using a UCG derived syngas is ongoing. It is reported that this operation is to be moved to Arkaringa in South Australia for commercial-scale development (see Section 5.1.1). The Bloodwood Creek development will initially involve power generation, but is planning to diversify into the production of chemicals such as ammonia for the production of ammonium nitrate, and possibly into liquid fuels production. In China it is planned to supply syngas to a two 10 MWe turbines and to a 20,000 t/y methanol plant (see Section5.4).

Chemical synthesis, and in particular the Fischer-Tropsch process, requires a higher grade and consistent syngas whose production has not yet been demonstrated on a commercial scale. Large- scale UCG with gas blending from several parallel reactors should be able to provide a consistent and reliable syngas feed, but this has yet to be demonstrated (Beath and others, 2007). A UCG activity that is tuned for optimal gas production for power generation will inevitably produce some liquid products as well, comprising both aqueous and hydrocarbon streams. This offers an opportunity of combining both industries and producing power and liquid chemicals/fuels at the same time (Van der Riet, 2009).

The raw syngas should generally be used on or near the site where it is produced as the economics of pipeline transportation are not particularly favourable (Energy Economist, 2008). The upgraded products may then be transportable by pipeline or in tankers.

The syngas composition will be dependent on the gasification conditions (pressure and temperature), the coal being gasified, whether or not the oxidant is air or is oxygen enriched and how much steam is present. In a commercial-scale application it would almost certainly be averaged out from four or five gasification chambers at different stages in their ‘life’. It should thus be possible to maintain a reasonably

Underground coal gasification 105 AIR OXYGEN

100% 14

12 80%

10 (dry, STP) (dry, 3

60% 8

6 40% Product gas, volume% (dry) Product

4

20% Gas calorific (heating) value, MJ/m

2

0% 0

Mars

Mars

Mars

Xinhe

Xinhe

Thulin

Xiyang

Xiyang

Gorgas

Angren

Suncun

Angren

Suncun

Gorgas

Gorgas

Krutova

Hanna I Hanna

Alcorisa

Gorlovka

Hoe Ck I Ck Hoe

Gorlovka

Gorlovka

Gorlovka

Liuzhang

Gorlovka

Liuzhang

Hanna III Hanna

Goriovka

Rawlins 2 Rawlins

Chinchilla

Pricetown

Hanna IIB Hanna

Hanna IIA Hanna

Hanna IIC Hanna

Hanna IID Hanna

Xiezhuang

Lisichansk

Lisichansk

Hanna IVA Hanna

Hoe Ck IIA Ck Hoe Lisichansk

Lisichansk

Hanna IVB Hanna

Lisichansk

Centralia B Centralia

Centralia A Centralia

Rawlins 1A Rawlins

Hoe Ck IIB Ck Hoe

Rawlins 1B Rawlins

Hoe Ck IIIB Ck Hoe

Hoe Ck IIIA Ck Hoe

Podmoskovia

Podmoskovia

Rocky Mtn 1A Mtn Rocky

Rocky Mtn 1A Mtn Rocky

Yuzhno-abinsk

Yuzhno-abinsk Leninsk-Kuznets CH CO H CO other gases 4 2 2

Figure 28 UCG syngas composition from various trials (Mark, 2008)

consistent syngas composition from the UCG operations. The results from different UCG trials are shown in Figure 28.

These illustrate the wide range of different conditions used in UCG trial work in various parts of the world, principally in the USSR, USA, and China, with one result from Australia at Chinchilla. They also illustrate the differences between the use of air as the oxidant, and of oxygen-enriched air (or oxygen/steam).

The gas from an UCG operation commonly has a methane content which is similar to that from a moving bed gasifier. This is probably because of the low exit temperature which promotes the formation of CH4 via the reaction of H2 with the char. Another factor which can contribute to a high methane content is the release of the CH4 trapped in the pore structure of the coal, and this is likely to be a bigger factor in deeper seams.

The production of the higher hydrocarbons in UCG is also typically higher than that from an entrained flow or fluidised bed surface gasifier (where the operational temperature is closely controlled). The lower reaction temperatures in parts of the UCG reactor result in relatively low rates of thermal cracking of the hydrocarbon molecules. However the hydrocarbon yields are typically found to be higher than those from a moving bed surface gasifier, presumably because some of them are cracked in the higher temperature region underground (Perkins, 2005). This is of significance if the syngas is to be used for liquids production.

BP have recently been taking a significant interest in UCG, and have formed a number of links and partnerships. In an overview paper entitled UCG syngas: product options and technologies, Puri (2006) outlines the options, see Figure 29. The analysis suggests that the syngas from UCG has high potential for use in the power generation market, and is feasible for the production of liquids. With CCS it could

106 IEA Clean Coal Centre CO + 2H 2 synthesis gas

hydrogen synthetic crude methanol

H power 2 refinery products acetic acid fuel and additives

ammonia formaldehyde DME

clean diesel naphtha

lubrication oils jet olefins

Figure 29 Tomorrow’s syngas to products business (Puri, 2006)

offer a low carbon route for the production of hydrogen and other fuels.

With current development projects, discussed in more detail in Chapter 9, at Majuba in South Africa, it is intended to use the syngas for power generation. At Chinchilla/Arkaringa, it is intended to use Fischer- Tropsch synthesis and at Bloodwood Creek the current proposal is to use the syngas for power generation and for ammonia and chemicals production. None have yet produced syngas in commercial- scale quantities to establish how consistent the quantity and composition can be, although good results from Bloodwood Creek have been reported.

Srinivas and others (2007) have carried out a simulation to assess the feasible range of steam-to-oxygen ratios which can be used if the syngas is to be used for Fischer-Tropsch synthesis (FTS). The simulation looks at a subbituminous coal and a lignite and illustrates some wide variations. The FTS requirements and process conditions are discussed in more detail in Couch (2008).

The overall FTS reaction is represented typically by the equations:

→ CO + 2.15H2 hydrocarbons + H2O (for the high temperature FT process with cobalt catalyst) → CO + 1.7H2 hydrocarbons + H2O (for the low temperature FT process with iron catalyst)

The amount of CO2 in the UCG syngas depends largely on the steam-to-oxygen ratio in the gasification chamber. That in turn depends on the steam which is injected, but it will also depend on the moisture already held in the coal and on water flow from surrounding strata into the chamber.

It is necessary to clean and treat the raw syngas appropriately, to separate and remove CO2, and to remove components which might poison the catalysts used. If the CO2 content of the syngas is too high, then under the right conditions the reverse water gas shift (WGS) reaction can be used:

CO2+H2 a CO+H2O

Underground coal gasification 107 9 Carbon management

Because of the perceived need to reduce the emissions of greenhouse gases, the question of the potential for CCS has emerged as a key aspect of the development of any coal-based technology. It is likely that there will be increasingly stringent limits set on GHG emissions, any technology development connected with coal such as UCG, needs to be able to address the questions which arise. The issues are discussed by Beath and others (2001), and in Carbon management and underground coal gasification (Friedmann and others, 2007a).

In relation to UCG, the syngas produced will undoubtedly contain significant amounts of CO2, but this can be separated using reasonably well established technologies. It is an area where a considerable amount of work is ongoing to reduce the costs involved. From the syngas, the CO2 will almost certainly be more easily separated when the oxidant is oxygen or oxygen-enriched air than when it is just air, because of the diluent nitrogen present. The processes involved are similar to those being considered for the reduction in CO2 emissions from coal combustion.

The composition of the product gas can be manipulated to maximise its hydrogen content through adjustments to the gas feed rates, water addition rate and the operating pressure in the underground gasification zone (although this is heavily influenced by the coal seam depth). On the surface, gas clean-up processes can be used to remove sulphur-containing gases, and further composition adjustments can be made through the use of a catalytic WGS reactor. This can be used to maximise the amount of hydrogen in the product gas. The amount of adjustment needed will depend on the eventual product gas use (Beath and others, 2001). If required, hydrogen can be separated, leaving a separate stream with all the carbon-containing gases. The separate combustion of the two streams allows for a flue gas stream containing only water vapour and nitrogen, which a carbon dioxide rich stream can be generated at high pressure for disposal and storage.

The other requirement is that after carbon capture (the separation of a CO2-rich gas stream), it will need to be pressurised, transported and buried somewhere where it is going to stay for at least several centuries, and preferably for some thousands of years. The chief geological targets for carbon storage include deep saline aquifers, depleted natural gas fields, and active or depleted oilfields (where CO2 injection can be used to enhance the amount of oil recovery).

There has been a considerable amount of discussion about the possibilities of storing CO2 in the cavities formed by UCG, and this has been used as a way of ‘promoting’ the technology. In their commentary, the LLNL is always careful to say that storage in UCG cavities has yet to be established as a practical and commercial possibility (Friedmann and others, 2007a; 2008a). Storage in the cavities would imply that the caprock above has not been fractured, and there is far too little experience so far to establish whether this will be the case in many situations.

In relation to CCS there seems to be a high degree of coincidence between coal resources and potential storage sites in China, India and the USA, although this is not the case in Australia and South Africa where developments are taking place. The economics of CCS would be greatly improved if there are nearby possibilities for using the CO2 for EOR, and where the operational pressure is higher (in deeper seams), and the product gas temperature higher, possibly equivalent to that from a surface gasifier. These requirements place further constraints on the sites where UCG might initially be developed. The economics of the operation will also be affected by the preference for using an oxygen-enriched feed, necessitating an on-site ASU, although there is a trade-off with the higher value syngas produced.

Carbon capture A number of technologies exist for separating CO2 from other gases. If the syngas is used for power generation then the separation might take place either before or after combustion. There are also opportunities for either partial or full CO2 separation (Friedmann, 2008). The processes can be conveniently classified as: G sorbent systems, wherein a liquid sorbent is used to preferentially adsorb/absorb CO2 in the first stage. The sorbent loaded with CO2 is then sent to the next stage where the sorbent is regenerated and recycled back. The stripped CO2 is processed further to make it ready for storage. Examples of such systems are amine-based CO2 absorption systems. At least three commercial processes using liquid sorbents are available including Selexol; G membrane separation, wherein a selective membrane is used to preferentially allow either CO2 or the non-CO2 gases to pass through the membrane; G cryogenic separation, where the entire gas mixture is liquefied, and the gaseous components are separated by distillation and/or using pressure swing absorption as in the Rectisol process (Burton and others, 2006; Friedmann, 2008).

It is clear that not all these technologies will be suitable for any given case, and specific assessment will be required to select the best for a particular application. Detailed descriptions for most of the

108 IEA Clean Coal Centre technologies can be found in Halmann and Steinberg (1999). There have been two recent reviews in IEA Clean Coal Centre reports, Post combustion carbon capture from coal fired plants – solvent scrubbing, Davidson (2007), and a parallel report on the application of solid sorbents and membranes, Davidson (2009). While most of the work to date has concentrated on capturing the CO2 from power plant emissions, the principles involved for its capture from other sources, including the syngas from a UCG operation, are much the same.

Carbon storage A lot has been written about storage of carbon dioxide in geological formations. Most notably in Geologic storage of carbon dioxide – staying safely underground (IEA GHG, 2008) and in the discussion in Friedmann (2008).

In geologic storage, CO2 is injected under high pressure into deep stable rocks in which there are countless tiny pores that trap natural fluids. Some types of rock formation have securely trapped fluids, including CO2 (and methane) for periods of millions of years.

Several types of rock formation are potentially suitable for long-term CO2 storage. These include: G depleted oil and gas reservoirs; G deep saline aquifer formations; G unmineable coal seams.

Deep porous rock formations with trapped natural fluids such as oil, natural gas or highly salty and unusable water are common throughout the world. The same geological forces that kept the original fluids in place should also secure the CO2. Once injected, the CO2 will be trapped, initially in tiny pores in the rock. Over time it will dissolve in any water in the rock formation and then may combine chemically with components in the rock to hold it even more securely.

Two projects at Weyburn in Canada (from 2000) and Sleipner off the Norwegian coast (from 1996) have already successfully stored some 5 Mt and 10 Mt respectively of CO2, and extensive monitoring has detected no leakage. During the coming years there are likely to be many more such demonstrations, such as the ones at In Salah in Algeria and the K12B project in the Netherlands, both of which started in 2004 (IPCC, 2005). By the time that UCG becomes a more mature technology with the potential for expansion, there should be a good body of experience with carbon storage on which to draw.

In terms of concept, the physical and chemical processes involved, likely targets, and of costs, storage in conventional target locations with gas from an UCG operation would be very similar to any other CCS stream. Secondary issues, such as the co-storage of contaminant gases (such as H2S), would also be similar.

There is, however, a need for improved storage capacity estimates at global, regional and local levels, and for a better understanding of long-term storage, migration and leakage processes. Addressing the latter issue will require an enhanced ability to monitor and verify the behaviour of geologically stored CO2. The implementation of more pilot and demonstration storage projects in a range of geological, geographical and economic settings will be important to improve our understanding of these issues (IPCC, 2005).

As for the regulation of UCG activity, current knowledge about the legal and regulatory requirements for implementing CCS on a large scale is still inadequate. There is no appropriate framework to facilitate the implementation of geological storage and take into account the associated long-term liabilities. Clarification is needed regarding potential legal constraints on storage in the marine environment (ocean or sub-seabed geological storage). Other key knowledge gaps are related to the methodologies for emissions inventories and accounting (IPCC, 2005).

It is unlikely that the operations of UCG and CCS would interfere geologically. In conventional storage, CO2 would be injected as a supercritical phase, requiring injection into formations at a depth typically greater than 800 m. For shallow UCG projects (<500 m), substantial rock volumes would separate the CCS and UCG efforts, and it is unlikely that there would be any substantial mass transfer between them. Although there may be some pressure transfer from the storage reservoir at depth into the UCG strata, these pressure changes should be small relative to the pressure changes associated with gasification, and as long as cavity pressure remained at or slightly below hydrostatic, transport should not be affected. It is thus unlikely that there would be any substantial interference between UCG and CCS components which could be treated independently.

Combined UCG CCS strategies It is claimed that UCG provides some inherent synergies to facilitate CO2 separation and its long-term geological storage, but as with CCS from coal-fired power plants the technology is at a very early stage of development.

There is a substantial programme under way at Aachen University in Germany in conjunction with

Underground coal gasification 109 DMT GmbH. This involved the conceptual design of economic and environmentally friendly UCG-CCS applications. The concept is discussed by Kempka and others (2009). The aim of the programme named CO2SINUS is to evaluate a low emission power plant based on the utilisation of syngas from a UCG operation, with emphasis on placing free-gas and adsorptive CO2 in the resulting gasified coal seams (CO2SINUS, 2009). The project envisages undertaking the preparatory scientific work for the implementation of a large-scale field test. It is currently at the process concept stage.

There will be some sites with potential for UCG development where there will be the possibility of using the CO2 captured for EOR. Others may lie near prospective saline aquifers for long-term storage. Site selection should include questions relating to CO2 storage such as injectivity, capacity and effectiveness. In addition any storage sites will need to be monitored. In terms of injectivity, the rate of volume injection needs to be assessed and must be sustainable over a period of several years. The site capacity involves an estimate of the total volume available, and its sensitivity to trapping mechanisms. The effectiveness of the site involves its ability to store the CO2 long beyond the lifetime of the project, potentially for hundreds of years. This last criterion is the most difficult to define or defend (Friedmann and others, 2007a) as it is impossible to demonstrate with absolute certainly in the short term although there are many known geological formations where gases have been trapped and held for many thousands of years.

One of the hindrances to carbon dioxide separation/removal from the product gas stream is the potential costs involved. If the product syngas is to be used for power generation, then not only is there a cost involved in the separation plant but there would be an effective ‘derating’ of the power plant, meaning that for a given output a larger and more costly installation is needed (Beath and others, 2001). Underground gasification has the advantage that the capital costs of a surface, conventional, gasifier (and of the mine to supply coal) would be much higher. In addition, when UCG is being applied to deeper coal seams in the future the higher operating pressures possible will be advantageous in terms of reducing the costs of providing the eventual CO2 stream for storage.

Much more practical and well monitored work on UCG CCS combined operations will be needed before it can be established whether the processes can be used in commercial-scale operations in the future. In July 2009 Carbon Energy in Australia (see Section 5.1.2) announced a partnership with ZeroGen to demonstrate a combined UCG CCS operation from the Bloodwood Creek pilot to store the CO2 from a 20 MWe generator (Stockwatch, 2009).

110 IEA Clean Coal Centre 10 Key requirements during the next five years

In its review The urgency of sustainable coal the NCC in the USA concluded that while UCG appears to be commercially ready in many contexts, there remain several key scientific and technical gaps (Nelson and others, 2008). These could be addressed by an accelerated research programme which is discussed in more detail in Section 10.2. It would build on existing knowledge, planned commercial tests, and advances in engineering and earth science simulations.

The main hindrances to the large-scale commercial development of UCG are associated with: G a lack of short-term competitive advantage where there are secure low cost alternative sources of energy in the form of natural gas and/or mined coal, and based on established technologies; G operational risks due to its unproven performance on a large scale, and the considerable number of operational problems that have occurred during trials in the USA and in western Europe; G uncertainties connected with its environmental performance; G public perceptions of a technology which has been poorly explained; G inadequate coverage and reporting in the literature, with contradictory information presented from various sources; G a lack of clear guidelines for site selection and characterisation since most published criteria only provide the basis for a preliminary screening exercise in locally understood strata; G a lack of clear guidelines for regulators, and complex overlapping jurisdictions in many places; G a shortage of people both in academia and industry with the necessary interdisclipinary management and technical skills to bring big projects to a successful conclusion.

The reason why UCG has not been pursued with greater vigour until quite recently has been the ready availability of relatively cheap energy (either coal or natural gas) in many of the places where it might have been developed. Where there is little or no economic advantage in using UCG its ‘untried’ status is a disincentive to investment. That hindrance will disappear as the costs of other fuel sources rise, and countries become more conscious of issues connected with supply security. Provided the current pilots in Australia, Canada, China and South Africa, grow in size to become significant demonstrations and show the potential for the competitive production of energy without environmental problems, UCG is likely to be much more widely applied.

It seems probable that each potential UCG site will be unique, as in many senses, is every underground mining site. It needs to be remembered that conventional mining techniques developed over many decades and that the necessary rules governing the conditions for safe extraction have been heavily influenced by the results of many serious accidents involving loss of life, and the flooding of underground workings by uncontrolled water inflows. While UCG involves entirely different risks, particularly in terms of the possibilities of water contamination, and there will be no men working underground, the many uncertainties need to be properly assessed and investigated.

The whole technology would benefit enormously from a much greater exchange of information and knowledge between the companies and research institutes involved, although in a competitive market this may be difficult to achieve. It is difficult enough to describe what is going on underground and the added ‘layer’ of secrecy and inadequate explanation in published material is unhelpful (as this author has found). As the potential is so huge, developers should see the benefits of such open exchange, but it does not seem that this is widely practised. The existence of two ‘rival’ series of international UCG conferences in London and Houston in recent years, largely attended by different groups of people is symptomatic of the problem, as is the lack of comment from several major players on the content of this report, even though they were sent draft copies.

One way of encouraging a more open approach to information is for there to be continued government sponsored research and development with the outcome(s) and results put in the public domain as happened with the US DOE programme in the 1970s and 80s. In a similar way, the work of the UK DTI has resulted in several detailed and useful reports, as has that of the CSIRO in Australia. Currently the approach of many of the companies to what they regard as their IP, is in danger of constraining the successful development of UCG, and of increasing the risks involved. As the technology is only just emerging, and is at a stage when commercial-scale operations are a real possibility but involve many uncertainties, such government support would seem to be well justified.

10.1 Undertaking demonstration-scale projects

Most of the current work has been at pilot scale, and during the next five years the main objective in relation to UCG development should be to run a number of demonstrations in relatively favourable circumstances in terms of seam depth and thickness and of the associated geological formations and the associated hydrogeology. Tests in seams at greater depth can perhaps wait until there is a more secure

Underground coal gasification 111 body of knowledge based on successful demonstrations in the 200–500 m deep range. The demonstrations would involve operating several UCG reactors/panels in parallel and establishing how consistent the syngas supply can be in terms of both composition and quantity.

Carrying out work on a demonstration scale (possibly with zero profit) and then on a larger commercial, profit making scale is already envisaged: G at Majuba in South Africa; G at Bloodwood Creek in Queensland, Australia; G at Chinchilla, Queensland, followed by development at Arckaringa in South Australia; G at Kingaroy in Queensland; G in Alberta, Canada; G at Wulanchabu in Inner Mongolia, China; G and possibly the Linc Energy and GasTech developments in Wyoming, USA together with that by Promgaz in the Kuzbas in Russia and Sasol in South Africa.

Carbon Energy in Australia have published detailed proposals for commercial-scale UCG development with a clear explanation of the technical basis for the expansion from a pilot-scale trial (Mallett, 2007). The plant design basis is illustrated in Figure 30 with three parallel UCG modules. The design allows for mixing the syngas from panels at different stages of development. It shows modules consisting of three parallel production wells, separated by coal panels 60 m wide which are left in place. The commercial- scale development at Bloodwood Creek may involve up to ten panels in parallel. UCG using the parallel CRIP method will be like longwall mining, but with more of the coal removed, and the ash staying behind underground. The minimum depth for large-scale extraction is thought to be 250–300 m, and above that, only partial extraction is safe.

With the operation of several demonstration-scale plants it should be possible to provide a much better assessment of the overall costs of UCG, and to project these into the future to cover the 20–25 year life of a large development. However, commercial secrecy may in practice inhibit such knowledge sharing, probably to the detriment of the speed with which UCG becomes more widely used, making the role of the regulators more difficult, and increasing the risk of environmental accidents.

10.1.1 UCG economics Various assessments have been made about the costs associated with setting up and running an UCG operation. Most estimates made by those promoting UCG projects tend to be somewhat optimistic. The difficulty in assessing the economics of any specific proposal is that it is necessary to forecast, project (or perhaps more precisely, guess) what is going to happen to a wide range of costs and prices over the next 25 to 30 years, so there are huge uncertainties attached to the figures. One of the hurdles to be overcome for the commercial use of UCG is assessing the technical risks involved, which are primarily those associated with the geology and hydrogeology of the coal deposit.

Only when operational results have been obtained and lessons have been learned from the first group of demonstration plants will it be possible to assess the contribution which the technology is likely to make in the longer term. This is unlikely to be for another five years, and might take longer as the demonstrations need to run for two or three years to sort out teething problems, and environmental problems may take a while before they emerge. Because the projects involve high up-front capital costs, and it is quite challenging to ensure that environmental requirements can be met, the schedules for the various feasibility studies being undertaken may be extended in order to get the necessary information to justify any financial investment.

The economics of UCG are firstly dependent on the geological setting of the coal and of the land use on the surface. The geological setting in terms of the nature of the various layers in the strata over the coal, and the local hydrogeology, and includes coal seam thickness, depth and quality.

Costs will also depend on the state of technical development of the various possible methods of carrying out UCG. The technology is just now moving from the pilot stage to possible demonstration-scale operations in four or five places in relatively shallow and favourable settings, while commercial-scale activities are still being planned. The coal seam depth and geological setting will directly impact on the costs of drilling, as will the ease of making the necessary underground linkages in the coal seam which will affect well spacing. Environmental risk will be a key determinant.

Coal seam depth will also affect the operating pressure thus affecting the nature and quality of the syngas produced.

The overall economics of any given UCG operation will be strongly affected by the oxidant used (and whether it is air or oxygen/steam). This largely determines the composition and heating value of the product syngas which then alters the options for its use and the value of the final products produced. The

112 IEA Clean Coal Centre a) Module design most basic application for the syngas is as a supplementary fuel for example in a coal-fired boiler. In >100 m ignition well an existing boiler up to 20% of the fuel can be syngas, but above this level boilers would need to be assessed on a case by case basis (Davis 2009). It may also be used in appropriately designed gas turbines or as a feed to chemical or Fischer-Tropsch synthesis processes for the production of liquid chemicals or transport fuels. There are a wide range of options depending on the composition and consistency of the syngas, and on the local markets for different products. The cost of the oxidant will be higher if an ASU is needed to provide oxygen, although the cost of subsequent CO2 capture may be significantly reduced. Local environmental requirements will determine the need CRIP for CCS. Storage possibilities and the costs will depend on whether there is any opportunity for using the CO2 for EOR or whether it needs to be injected into a deep saline aquifer. injection well There will also be the costs of the necessary infrastructure to support site operation. These may include the construction of new roads, a link to and from the power production well vertical well supply grid together with storage tanks, an administration and laboratory block. There will be a power generation unit and/or a chemicals production plant as generally the heating value of the syngas will not be high enough to justify piping it a long distance to remote users.

The scale of the long-term development of UCG processes will be dependent on: G the results obtained from the first five or ten pilots, and whether or not they are followed by demonstrations; G the ease with which groundwater contamination can be avoided; G the validation of various models to assist with process b) Parallel modules (module life 2.3 years) control; G whether or not the syngas produced is consistently of sufficient quality to facilitate the production of higher value products (for chemicals production and/or 1st module methanol or Fischer-Tropsch synthesis); G the availability of specialist equipment, skilled labour and of contractor capacity (also referred to in Section 10.5); 600 m G requirements of permitting and of the various local regulations relating to environmental issues, including CCS.

2nd module The potential costs of UCG It is difficult to extract meaningful economic data from the goaf 3rd module literature, since what is published often has some kind of ‘agenda’ behind it. However, generalised and published 180 m information and data can be helpful in gaining a broad 60 m burn progress understanding of what is involved. In the right updip circumstances, UCG undoubtedly has the potential for the production of lower cost electricity and of a range of chemicals from the syngas when compared with using other methods and raw materials. Most cost estimates which have been published are at the ‘pre-feasibility’ level of accuracy based on limited geological data and very limited operating experience. As operating and contractual Figure 30 Plans for UCG expansion to commercial experience widens, both the risks and the costs will be scale using parallel CRIP (Mallett, 2007) clarified, and the potential for the use of UCG on a wider scale will become clearer. This process will take a number of years.

One of the best available economic assessments of a UCG application is included in a study undertaken by the Wyoming Business Council in the USA (GasTech, 2007b). The design basis is an air-based UCG operation producing syngas for a 200 MWe IGCC power plant or for an oxygen-blown UCG for a

Underground coal gasification 113 FT liquids production facility. It looks in some detail at the sensitivity of the costs to: G seam depth and thickness; G well spacing; G syngas heating value; G resource recovery.

Plant location UCG operations are likely to be located near large reserves of otherwise unmineable coal in reasonably thick seams where the geology is environmentally friendly and the risks low. They are likely, initially, to be mainly in relatively remote places where the land on the surface is largely undeveloped, and there will be some costs associated with infrastructure development. These would include the provision of roads and of power lines both to supply electricity and, if there is an on-site power plant to take the power generated to the grid.

The economics of an UCG operation will be strongly affected by future requirements for CO2 capture and sequestration. In terms of plant location, if there are nearby places where CO2 can be readily or even profitably sequestrated for example in depleting oil wells or in exhausted natural gas reservoirs, then the costs can possibly be contained. Future research and development may establish that CO2 can be stored in adjacent coal seams or even in the caverns formed by UCG.

Developing an economic model Much more information is needed about the relative costs of drilling a closely spaced grid of vertical holes compared with inclined and in-seam holes which may be up to 500 to 700 m long. The drilling also depends on the quality of the exploration data available. It is highly desirable that an economic model is developed to cover all aspects of an UCG operation. This would include both surface and sub-surface aspects. It should be looking at a production scale operation with a design layout which ensures effective use of the coal asset in a particular location and to be able to compare different UCG approaches (Sallans, 2009). To build and validate a useful model, the developers will need to share more of their experience and knowledge, and this would make a significant contribution to the potential for UCG use.

10.2 Establishing a science and technology roadmap

Coincident with better discussion and increased openness between the developers, it would be helpful to set out a science and technology roadmap. This would identify technology gaps and could ensure that those working in different academic establishments undertake complementary projects. There are active groups in Australia (at CSIRO and at the University of Queensland); in China (at the CUMTB); in the UK at several universities (Cardiff, Heriot-Watt, Keele, Imperial College, and Newcastle) and in the USA at the LLNL and at Purdue University in Indiana.

Universities could be encouraged to team up with industrial partners which would help develop relations between industry and academia in connection with UCG but could help in terms of getting information into the public domain by means of scientific papers (Turner, 2009). These could be beneficial in cross- validating the work done in different places.

There is a huge amount of work to be done in validating and developing the various models which have been proposed. It is essential to clarify various aspects relating to site selection and screening, and to operational and shut-down procedures. In addition, techniques need to be developed which can monitor what is going on in the underground reactor in a meaningful way which might pave the way for providing real-time process control. More insight is needed into the potential hazards associated with ground movement and of groundwater contamination. The issues are discussed by Upadhye and others (2006).

In terms of estimating the coal reserves in which UCG might be applicable, a great deal of work needs to be done to interpret geological information, as there is very limited experience of the effects of carrying out gasification reactions underground, the development of cavities and the thermal effects on surrounding strata.

The roadmap proposed by NTPC in India includes some useful guidelines (NTPC, 2006): G framing appropriate regulations for UCG operations (see also Section 10.3); G estimating the coal reserves where UCG might be carried out; G initial site selection(s) based on existing geological data; G mapping and assessment of the sites for suitability for UCG; G establish the cost parameters within which the process would be competitive; G carry out comparisons with other possible technologies; G identifying which UCG technology would be appropriate: – to achieve the necessary syngas quality and availability on a continuous basis; – to address environmental concerns; – to identify the economic capacity for a power plant;

114 IEA Clean Coal Centre – to achieve the cleaning of the syngas; G selection of the UCG technology; G identify a semi-commercial site; G develop a pilot UCG operation to provide first hand experience with the technology which would facilitate a realistic cost assessment.

In the USA the National Coal Council recommended that a substantial renewed research programme be started. This should involve research institutions, universities and companies. The programme should include a detailed engineering analysis of each step in the entire process, along with thorough economic analysis. Following the US DOE programme from 1973 to 1989, many issues remain unexplored, including: G subsurface process monitoring and control; G the assessment of risks and hazards; G synergies with carbon management; G improved simulations/models to define cavity formation, gasification reactions, the flow and transport of contaminants and of subsidence.

In any such programme, it would be important to engage with field demonstrations as these can provide the platform for testing subsurface monitoring equipment, to validate models and simulations and to understand potential environmental impacts and concerns. The knowledge gained could be used to develop standards, since at present there are no broadly accepted guidelines for the siting and operation of UCG projects. To help commercialisation in north America, the NCC recommends a 3–5 year research programme aimed at providing key industries, regulators and decision makers with the technical basis needed to screen out problem sites and encourage sound investment (Nelson and others, 2008).

10.3 Regulatory harmonisation

It may be that differences will remain between the regulation in different countries (and even between different states within a country) because they have arisen on a historical basis and are not necessarily consistent across territorial boundaries. The first places to tackle are obviously where UCG development might take place during the next few years, and where it is under serious consideration. It would clearly be helpful to have examples of where the regulatory regime handles the issues of land ownership and use, and of the minerals under the land and of their extraction, in a straightforward way. This can then be harmonised with the existing procedures for preparing EIAs, and for the necessary surface installations associated with an UCG operation.

10.4 Improving the public perception of UCG

This is an area which has had inadequate attention during the development phases of UCG. Some proposals for development in the UK around the Silverdale colliery were deflected and dropped, because of local public opinion.

A study undertaken by the Tyndall Centre in the UK used a literature review and a focus group (Shackley and others, 2004). Its main recommendations were that in order to build up trust with local communities where UCG might be deployed, it is desirable to: G develop UCG on a small scale in order to obtain mastery of the process and of potential innovations in an incremental fashion; G only develop UCG in conjunction with policies promoting CCS; G include UCG in a package of measures which would improve the local communitie’s quality of life, economy, environment and employment; G ensure that all operations, operators and other responsible parties are transparent and open in their dealings with both the public and regulators. Clear and accurate information is needeed with opportunities for community representatives to cross-examine the ‘experts’; G include local stakeholder and public reactions as part of the site selection process alongside more tangible issues such as the geology and hydrogeology of the strata, and other planning issues; G undertake a professional communication strategy before any trial is undertaken, with an ongoing stream of information on a website and through appropriate publications.

Few studies have been done, and part of the poor image that UCG has amongst some sections of the public is that the technology has been poorly explained, and the risks involved have either been ignored or seem to have been glossed over. The public are not impressed when exaggerated claims are made. There is thus scope for a considerable amount of work, particularly in places where development is being considered, to provide good explanation(s) and information. The completion of some successful demonstrations and open publication of the results, including a thorough geological analysis and commentary, would provide an excellent basis for providing such information.

The programme recommended by the NCC in the USA, discussed in Section 10.2, could also provide the

Underground coal gasification 115 basis for education and outreach about UCG since few decision makers are familiar with UCG as a technology option. The US DOE could then usefully develop briefing materials and public outreach documents that could be used as information resources (Nelson and others, 2008).

10.5 Meeting the skills shortage

There is a serious skills shortage relating to people with the necessary experience and knowledge for designing, setting up and operating an UCG plant. Many of those involved in earlier trials have moved on and/or retired. The sites where UCG may be exploited may be quite remote, which brings its own limitations and challenges.

The technology requires the exploitation of a unique mixture of inter-disciplinary skills. It suffers because it needs: G drilling expertise from the oil and gas industries (although some of the requirements are somewhat different). There is a lack of experience in in-seam coal drilling, except in a few places; G geological and hydrological expertise, but the basis is different from that for conventional coal mining; G chemical process engineers, most of whom would be unfamiliar with such an ‘uncontrolled’ process; G a project management team who can work together flexibly and maintain high standard of safety and of environmental management.

There is a need for more training courses, and the UCG Partnership in the UK are to be commended for starting this process, although there is a long way to go before such courses will address many of the issues listed above. The first need is for trainers, and while the obvious place to go is to universities, there is a need for people with a practical background as well as an academic one. Even in academia there are not many people with the relevant knowledge and understanding, and very few have even played an operational role in an active UCG development.

116 IEA Clean Coal Centre 11 Conclusions

UCG has the potential to unlock vast amounts of previously inaccessible energy in unmineable coal resources. However there are formidable obstacles to be overcome before this is possible, many of which are associated with the fact that the process takes place deep underground in a context where it is difficult (or impossible) to monitor and control the conditions. In the short term, one of the obstacles to sucessful development is that the major developers are not sharing their knowledge and experience.

It seems probable that each potential UCG site will be unique as, in many senses, is every underground mining site. Conventional mining techniques developed over several decades and the necessary rules governing the conditions for safe extraction were heavily influenced by the results of serious accidents involving loss of life. While UCG involves entirely different risks, particularly in terms of the possibilities of water contamination, there will be no men working underground. However the uncertainties need to be properly assessed, based on the emerging experience gained from the current projects.

UCG requires a multi-disciplinary integration of knowledge from exploration, geology, hydrogeology, drilling, and of the chemistry and thermodynamics of gasification reactions in a cavity in a coal seam. This involves rethinking almost all past experience connected with coal utilisation because there is commonly little contact and technical understanding between those who mine coal and others who use it. Even at an academic level, there are few experts who can cut across the boundaries between the geologists and mining engineers responsible for coal extraction, and the chemical and process engineers largely responsible for its use. In addition, many coal experts have developed an in-depth knowledge and understanding of their own coals and of their geological settings, but have limited practical knowledge of the coals and their associated geology which occur in other places. Where coal is mined, geological expertise is focused on its impact on conventional mine design, construction and operation, and in many places this is based on decades of experience. The behaviour of an UCG reactor/cavity is quite different and there is as yet very limited experience of what happens.

There has been a great deal of test work over a period of more than fifty years, particularly in the USSR during the 1950s and 60s and some of this has been described as ‘commercial’. A more accurate description is probably that some of it was on an industrial scale, since the concept of commercial profitability was rather different under the Soviet regime compared with that which would be applied now. Our understanding of the environmental standards to be applied has also changed. Only some 15–20 Mt of coal has been gasified in total, which illustrates the limited scale of the work undertaken, and UCG is described in the early 1990s by a prominent Russian commentator as ‘unstable and inefficient with respect to thermal power’.

In the 1970s and 80s there was an extensive programme of tests in the USA, and there have been other trials in various European countries as well as in China. These have all been in different types of coal, at different depth and using various techniques for linking the injection and production wells. Thus the results are quite scattered with a strong empirical basis, and few clear patterns have emerged that would guarantee a successful outcome in a new location, although a number of useful lessons have been learned.

It is unfortunate that some of the proponents for the use of the technology have used rather loose language when discussing it. The phrase ‘UCG is proven technology’ has been used when it would have been more accurate to say that ‘some aspects of it have been established in particular tests’. It has undoubtedly reached the stage of ‘proof of concept’, but different parts of the technology have been demonstrated/proved separately and each in unique circumstances (as is commonly the case with emerging coal technologies). Only now are the various steps being put together to establish UCG on a consistent and potentially commercial basis. It is likely to be several more years, when the Bloodwood Creek, Chinchilla and Majuba developments (and others) have reached a degree of maturity, before UCG can said to be ‘proved’. Each needs to establish relatively smooth operations for at least two or three years at demonstration and then commercial scale with no unacceptable environmental impacts before the word ‘proved’ can be used with confidence. The word would also apply only to similar coal deposits with similar associated geology, and as the technology is used in different circumstances, for example in different strata and hydrogeological settings, thicker seams, in lignites and in deeper seams, it will need further ‘proof’ under these circumstances. The schedule for commercial-scale development at Majuba envisages the commissioning of power plant units based on UCG syngas from 2017 onwards and progressively to 2020, following a demonstration-scale unit to be operating by 2013.

The single most important decision that will determine the technical and economic performance of UCG is site selection. Because of the lack of reliable and comprehensive data covering a range of coals at different depths and in different geological settings, it is difficult to define firm guidelines relating to where UCG might be developed. Virtually all the published guidelines are based on the deposits in a particular area and apply only to a particular range of coals, seam depth and of geological conditions.

Underground coal gasification 117 Since this qualification is commonly left unsaid, much of the published literature is misleading, and the criteria listed are more accurately described as a preliminary screening for sites worth further consideration and investigation.

The field trials undertaken so far are grouped into two main categories. Trials conducted at shallow depths, some in thicker seams, and those at greater depth in thin seams. While the trials included coals of different rank, the results have been too scattered to draw firm conclusions and all that has been established is that given the right conditions, coals of different rank can be gasified underground. Whether those conditions might be suitable for large-scale economic development has not yet been established and most of the trials have been of relatively short duration. No trials have been carried out in thicker seams at any depth below 300 m, although at the time of writing a trial is just starting in a seam of indeterminate thickness at a depth of 1400 m. One problem in discussing depth limitations is that different developers have taken different views largely based on the particular coals (and its geology) they are interested in, then publishing Outline criteria for UCG sites without taking into account the highly varied nature of coal deposits worldwide. People have put forward quite different and sometimes contradictory site criteria, largely based on their own coals and geology.

A good number of the past trials took place in seams less than 200 m deep, and were associated with gas losses (as the overburden collapsed or cracked) and in some cases with consequential water contamination. For example, the Hoe Creek trial in the USA which resulted in contamination was in a seam just 30 m deep, and was overpressurised at times which led to gas losses.

The fundamental issue is the surrounding geology and hydrogeology, and exactly what happens when a reactor at 1000ºC moves through the coal seam. There will be sites at most depths, possibly with an upper limit of (say) 100 m where it would be possible to use UCG. However it will mean a great deal more work and many more trials and demonstrations before the criteria can be more authoritatively spelled out, and even then they will vary from coalfield to coalfield.

The other issue is that seam depth affects the probable operating pressure – which is normally held at just below the prevailing hydrostatic pressure so that the gases are contained within a water-based envelope. The pressure increases by roughly 0.01 MPa/m for fresh water and 0.012 MPa/m for a saturated saline aquifer. Deeper UCG reactors can/will operate at higher pressures – which will affect the syngas composition and its handling on the surface. The higher pressures can bring advantages.

As the coal seam depth increases, drilling costs will increase, and the stability of in-seam holes may be affected. At the same time, operating pressures will also increase, which will affect the composition of the syngas. In thick seams there will be a more significant hydrostatic gradient from the top to the bottom which may affect the stability of operation as water inflow may be more difficult to control.

There are widely differing approaches being followed by those making plans in Australia and those making plans in Europe. For example, the requirement to operate the UCG cavity at just below the prevailing hydrostatic pressure and having a water seal to prevent gas leakage may relate mainly to shallower deposits. In Europe where deep deposits may be exploited a depths between 500 and 1500 m, a water seal may not be relevant where there is an impervious rock formation above the UCG cavities. The conflicting approaches relating to the possible need for a water seal compared with the need for a cap rock involve some gross oversimplifications of the nature of UCG. It seems likely that each UCG site will be unique, with some shallow sites having nearby water, and others being bone dry. Similarly some deep sites may be dry while others will have surrounding and overlying aquifers. Likewise the suitability of the cap rock for providing long-term seal can only be determined by a detailed rock engineering study including an assessment of the effects of UCG where temperatures in the coal seam cavities may reach well over 1000ºC.

Because of the requirement in some places for a water seal around the UCG reactor cavity, a successful test in terms of syngas quality at pilot scale does not establish that a commercial-scale operation is necessarily viable. The water table and supply source may be able to sustain the water seal around a small area, but when the scale of the operation multiplies by ten times, and later (possibly) by as much as a hundred times, there may be insufficient water to maintain the necessary seal.

Much more information is needed about the relative costs of drilling a closely spaced grid of vertical holes compared with inclined and in-seam holes which may be up to 500 to 700 m long. The costs and accuracy of drilling will depend on whether there are local experienced contractors. The drilling also depends on the quality of the exploration data available.

Surprisingly little attention has been paid to the variability of coal seam properties associated with their rank, grade (ash content) and depth. Tests have shown that coals of almost any rank can be gasified in principle, as they can in a surface gasifier. However the behaviour of coal, its ignitability for example, will vary. Much more work needs to be done before a range of coals can be used successfully by UCG. The current trials in Australia and South Africa are (quite rightly) being carried out in relatively favourable circumstances in terms of seam depth and thickness, and of coal rank and behaviour. Other

118 IEA Clean Coal Centre coals, particularly the higher rank ones, may be more challenging.

It is interesting to note that in the current trials, different technologies are being explored, namely: G air-blown gasification using vertical wells together hydrofracturing and reverse combustion to establish inter-well linkages at Majuba in South Africa (and shortly at Kingaroy in Australia); G air-blown gasification using in-seam boreholes to establish the links between vertical wells at Linc Energy in Australia (and shortly at Sasol in South Africa and Promgaz in Russia); G oxygen-blown gasification with steam injection at Bloodwood Creek in Australia using parallel in- seam boreholes.

Much of the current work at active test sites in Australia (both Bloodwood Creek and Chinchilla) and in South Africa at Majuba is taking place in subbituminous or high volatile bituminous coals. The Wyoming coals in the USA, where much of the test work took place and where development is planned are subbituminous. The lower rank coals are generally more permeable than higher rank ones which has implications for the ease with which linkages can be made between wells. Lower rank coals may also be somewhat softer, which could affect the stability of in-seam boreholes.

In relation to UCG development, there will be surface facilities including the access wells and associated pipework (covering a considerable area), gas cleaning units, and, generally a power generation plant and/or a liquids production facility. Thus UCG will be subject to all the familiar constraints. In addition there will be a whole number of geological constraints which are far less well understood as they have only been tested in limited circumstances. UCG takes place out of sight in a context where it is not possible to control many of the variables and it will be important to extend our understanding of the processes going on so that sufficient control can be achieved. Both monitoring and modelling will be of considerable importance.

Development needs include: G a cost-effective means of acquiring high-resolution coal seam geological data, and information on the surrounding strata and its hydrogeology; G reproducible drilling accuracy, particularly for in-seam drilling; G the parallel operation of multiple independent gasifier chambers with separate injection and production wells to ensure a consistent supply of syngas; G the validation of various models which have been proposed to represent various aspects of the process. In particular to understand the factors affecting the behaviour of the underground reactor, so that its performance can be predicted and optimised; G integrated surface plant for gas cleaning, followed by either IGCC power generation and/or for the production of liquids fuels or chemicals. G in the longer term, there is likely to be the requirement that UCG operations are associated with CCS.

Progress with establishing UCG as a viable technology is being held back for a number of reasons. These include: G a lack of understanding of the requirements of a successful UCG project by some of those who might provide the necessary investment; G an acute skills shortage of people with appropriate project management experience and of people and companies with the necessary drilling experience. Even in academia there is a lack of people with any kind of in-depth understanding of the practicalities and complexities of UCG; G a lack of understanding that the geological knowledge needed may be different (and possibly more extensive) than that needed for conventional underground mining. During the early stages of UCG development, for the next five to ten years, each potential site should be regarded as unique, thus requiring careful and detailed geological assessment; G a lack of enabling legislation in most countries which would facilitate appropriate development, and clashes between those who might be wanting to extract various underground resources including water, oil, gas and CBM, as well as the possible production of syngas from UCG. As a result, the regulators can have a difficult job in deciding which development might take priority; G the fact that the technology is being promoted by two industry groups whose activities may alternatively be regarded as complementary or competitive. There are two series of UCG conferences, running, apparently, in parallel. One is sponsored by the UK UCG Partnership, while the other is sponsored by the US Zeus Corporation. In a mature technology, competition can be regarded as potentially making a positive contribution to development. In a fledgling technology like UCG, cooperation would seem to offer great benefits to development; G the fact that the currently more advanced and successful UCG projects use a technology with certain proprietary aspects, which therefore makes it difficult to assess its potential for wider application; G the lack of government involvement and support, which is needed to ensure the spread of knowledge and understanding which would underpin the extensive deployment of a technology with enormous potential.

The next stages of development should be in places (geological settings and coal seams) where there is

Underground coal gasification 119 the best chance of success. Then, as more experience is gained, the boundaries of what it permissible can be gradually extended in tackling slightly more difficult situatons. There is a significant risk that premature development in the wrong place could result in environmental damage which would give the technology a bad reputation. This could happen if developers try to cut corners, and perhaps proceed without having done sufficient exploration or test and demonstration work.

Despite the many trials and a considerable amount of research, no commercial UCG project has yet been demonstrated. Even the Angren plant in Uzbekistan which has been operating for nearly fifty years does not meet the criteria of commercial viability. It is small, and uses old equipment which is fully depreciated. There have been no moves to scale-up the operation. Linc Energy who now own the plant are not considering any investment at Angren. In past operations for providing a fuel gas for the power plant the consistency and quality of the syngas produced has not been a critical factor, and the environmental standards applied would probably not meet current requirements in OECD countries.

The development of new technologies and the increase in the value of energy may change this situation, and there has been a great deal of progress during the past five years. Some projects such as those at Majuba in South Africa and Chinchilla and Bloodwood Creek in Australia are showing considerable promise, though even these are at an early stage of development. The current pilot tests should result in demonstration-scale plants within three to five years, and possibly commercial-scale plants within seven or eight years, providing greatly increased confidence in the technology. At Bloodwood Creek it is planned to demonstrate a combined UCG CCS operation, capturing and storing the CO2 from a 20 MWe generator.

In view of the potential value of UCG in terms of unlocking huge amounts of energy, tests and demonstrations in different settings are worth a substantial effort, but projects need careful assessment and to build on what has already been established. This, however, requires a high level of openness and thorough reporting of what happens during development and government supported programmes might help to keep knowledge in the public domain.

120 IEA Clean Coal Centre 12 References

ABC News (2009) Metro Coal expects ‘20,000 bpd’ from new project. ABC News. Available from: http://www.abc.net.au/news/stories/2009/05/29/2584052.htm, 1 pp (29 May 2009) ABNnewswire (2009a) Linc Energy Limited (ASX:LNC) Technology Update On Chinchilla Underground Coal Gasification (UCG) Operations. Available from: http://www.abnnewswire.net/press/en/60275/Linc-Energy-Limited-(ASX:LNC)-Technology-Update-On- Chinchilla-Underground-Coal-Gasification-(UCG)-Operations, 2 pp (10 Mar 2009) ABNnewswire (2009b) Linc Energy Limited (ASX:LNC) Commences Stage 1 of the UCG Project in Vietnam. Available from: http://www.abnnewswire.net/press/en/60485/Linc_Energy_Limited_ (ASX:LNC)_Commences_Stage_1_of_the_UCG_Project_in_Vietnam.html, 1 pp (20 Apr 2009) Ahner P F (2009) Personal communication. Consultant, Tulsa, OK, USA, PFA Consulting LLC, [email protected] (12 Feb 2009) Barone S P, Malavasic K F (1987) Underground coal gasification. Overview of an energy alternative. In: Proceedings of the 14th biennial lignite symposium on the technology and utilisation of low-rank coal. Dallas, TX, USA, 18-21 May, 1987. Grand Forks, ND, USA, University of North Dakota, 13 pp (1987) BCG (2008) Submission from BCG Energy Ltd. Available from: http://www.scottish.parliament.uk/ s3/committees/eet/inquiries/energyFuture/12EnergyLtd.pdf, 5 pp (Oct 2008) BCG (2009a) Projects. Available from: http://www.britishcoalgasification.co.uk/projects.html, Aberdeen, Scotland, UK, British Coal Gasification (BCG) Energy Ltd, 1 pp (21 Jan 2009) BCG (2009b) Firth of Forth UCG. Available from: http://www.britishcoalgasification.co.uk/News- item1.html, 1 pp (2009) Beath A (2003) Process studies for clean electricity and liquid fuels from UCG. Paper presented at the Beath A (2004) Gasification of coal in situ: United Kingdom and CSIRO research. CSIRO Exploration and Mining report 1168R, Kenmore, Queensland, Australia, CSIRO, 28 pp (Jan 2004) Beath A (2006) Session 2B: Process performance and economic viability. Tutorial session at The underground gasification workshop. Kolkata, India, 12-15 Nov 2006. Available from: http://www.fe.doe.gov/international/Publications/Tutorial_UCG_Session2_12Nov06.pdf, 7 pp (2006) Beath A (2009) Personal communication. CSIRO Energy Technology, Newcastle, NSW, Australia (23 Feb 2009) Beath A, Davis B (2006) UCG history. In: Proceedings of the underground coal gasification workshop. Kolkata, India, 12- 15 Nov 2006, Available from: http://fossil.energy.gov/international/Publications/ ucg_1106_history.pdf, 41 pp (2006) Beath A, Mallett C (2006) UCG modelling. In: Proceedings of the underground gasification workshop. Kolkata, India, 12-15 Nov 2006. Available from: http://fossil.energy.gov/international/Publications/ ucg_1106_modeling_csiro.pdf, 28 pp (2006) Beath A, Su S (2003) Gasification of coal in situ (with sections on the USA, Australia, NZ, China and modelling). CSIRO Exploration and Mining report 1110C, Kenmore, Queensland, Australia, CSIRO, vp (Jan 2003) Beath A, Wendt M, Mallett C (2000) Optimisation of underground coal gasification for improved performance and reduced environmental impact. Available from: http://www.australiancoal.csiro.au/ pdfs/min-bea.pdf, 8 pp (2000) Beath A C, Wendt M, Mallett C (2001) Underground coal gasification as a method for reducing the greenhouse impact of coal utilisation. In: Proceedings of the 5th international conference on greenhouse gas control technologies: GHGT-5. Cairns, Qld, Australia, 13-16 Aug 2000. Collingwood, Victoria, Australia, CSIRO Publishing, 1307-1312 (2001) Beath A, Craig S, Littleboy A, Mark R, Mallett C (2004) Underground coal gasification: evaluating environmental barriers. CSIRO Exploration and Mining report P2004/5, Kenmore, Queensland, Australia, CSIRO, 125 pp (Aug 2004) Beath A, Mallett C, Craig S, Mark R (2007) Simulating cavity growth, gas production and associated processing for underground coal gasification. In: Proceedings of Petrotech 2007 conference. Delhi, India, 15-19 Jan 2007. vp (2007) Berïiï G (2008) Personal communication. (18 Nov 2008) Biezen E N J, Bruining J, Molenaar J (1995) An integrated 3D model for underground coal gasification. In: Proceedings of the annual technical conference of the Society of Petroleum Engineers. Dallas, TX, USA, 22-25 Oct, 1995. Available from: http://cat.inist.fr/?aModele=afficheN&cpsidt=6303867; 929-940 (1995) Blinderman M, Maev S (2003) The Exergy underground coal gasification technology and the Chinchilla IGCC project: Canadian perspective. In: Proceedings of ‘Combustion Canada 03’ conference. 21-24 Sep 2003,Vancouver, BC, Canada, 15 pp (2003) Blinderman M S, Klimenko A Y (2007) Theory of reverse combustion linking. Combustion and flame. 150; 232-245 (2007) Blinderman M S, Saulov D N, Klimenko A Y (2008a) Exergy optimisation of reverse combustion linking in underground coal gasification. Journal of the Energy Institute. 81, (1); 7-13 (2008) Blinderman M S, Saulov D N, Klimenko A Y (2008b) Forward and reverse combustion linking in underground coal gasification. Energy. 33, 446-454 (2008)

Underground coal gasification 121 Bond P (2008) Personal communication. Managing Director, Linc Energy, Brisbane, Qld, Australia (1 Oct 2008) Bowen B H (2008) Underground coal gasification. Presentation to the Heritage Research Laboratory, Indianapolis, IN, USA. Available from: http://www.purdue.edu/dp/energy/pdfs/CCTR/presentations/ UCG-HeritageLab-10-21-08.pdf. 37 pp (21 Oct 2008) BP (2007) BP statistical review of world energy - June 2007. Available from: www.bp.com, Egham, Surrey, UK, BP Distribution Services, 45 pp (Jun 2007) Bradbury D (2008) Canadian firm to take clean coal underground. BusinessGreen. Available from: http://www.businessgreen.com/business-green/news/2232912/canadian-firm-clean-coal, (19 Dec 2008) Brand J F (2008) UCG pilot study in Secunda, South Africa – the experimental design and operating parameters for the demonstration of the UCG technology and verification of models. In: Proceedings of the 2008 Pittsburgh coal conference. 30 Sep-2 Oct 2008, Pittsburgh, PA, USA, CD-ROM, Pittsburgh, PA, USA, University of Pittsburgh, 11 pp (2008) Bruining H, Wolf K-H (2007) Underground coal gasification. Presentation given at the 2nd meeting of the European Commission Directorate-General Energy and Transport. Bilateral cooperation India. 28-29 Nov 2006, Brussels, Belgium. Available from: http://ec.europa.eu/dgs/energy_transport/international/ bilateral/india/energy/3_eu_india_working_group_energy_en.htm (2007) Burton E, Friedmann J, Upadhye R (2006) Best practices in underground coal gasification. Draft. US DOE contract no W-7405-Eng-48. Livermore, CA, USA, Lawrence Livermore National Laboratory, 119 pp (2006) Carbon Energy (2009a) Carbon Energy delivers major UCG syngas milestone. ASX announcement. Available from: http://www.carbonenergy.com.au/documents/major%20syngas%20milestone.pdf, West Perth, WA, Australia, Carbon Energy Ltd, 3 pp (13 Jan 2009) Carbon Energy (2009b) Carbon Energy in A$32 million capital raising to develop UCG project. Available from: http://www.proactiveinvestors.com.au/companies/news/1653/carbon-energy-in-32- million-capital-raising-to-develop-ucg-project-1653.html, 1 pp (5 Jun 2009) Chaiken R F, Martin J W (1992) In-situ gasification and combustion of coal. SME mining engineering handbook. 2nd edition vol 2. Chapter 22.6. Littleton, CO, USA, Society for Mining, Metallurgy and Exploration. p 1954-1970 (1992) Chandelle V, Li T-K, Ledent P, Patigny J, Henquet H, Kowol K, Masson G, Mostade M (1989) Belgo-German experiment on underground gasification. Demonstration project. EUR 12263 EN. Brussels, Belgium, Commission of the European Communities, vp (1989) CMTF (2008) Coal Mining Taskforce. Asia Pacific Partnership on Clean Development and Climate. Las Vegas, NE, USA, Sep 2008. Available from: http://www.asiapacificpartnership.org/Coal%20Mining/ CMTF_AUSTRALIAN_SLIDES_Las_Vegas_(2).pdf, 19 pp (2008) Coober Pedy (2008) Coober Pedy Regional Times. Available from: http://cooberpedyregionaltimes.wordpress.com/2008/11/19/arkaringa-basin-to-host-linc-coal-and-oil- operation/ 2 pp (19 Nov 2008) CO2SINUS (2009) CO2 storage in in-situ converted coal seams. Available from: www.co2sinus.org/index_en.html (2009) Couch G R (1993) Fuel peat – world resources and utilisation. IEACR/56. London, UK, IEA Clean Coal Centre, 118 pp (Mar 1993) Couch G R (2004) The potential for coal use in Pakistan. CCC/83. London, UK, IEA Clean Coal Centre, 39 pp (Apr 2004) Couch G R (2006) Ash management in coal-fired power plants. CCC/118. London, UK, IEA Clean Coal Centre, 69 pp (Oct 2006) Couch G R (2008) Coal to liquids. CCC/132. London, UK, IEA Clean Coal Centre, 114 pp (Mar 2008) Cougar Energy (2009) Kingaroy, Queensland – 400MW Power Station Project. Available from: http://www.cougarenergy.com.au/projects.html, 1 pp (2009) Covell J R (2007) US regulatory framework. Available from: http://fossil.energy.gov/international/ Publications/cwg_june07_covell.pdf, vp (Jun 2007) Covell J R, Thomas M H (1996) Combined air sparge and bioremediation of an underground coal gasification site. DOE/MC/31346-97/C0830. Paper presented at the Ninth Annual IGT Symposium on Gas, Oil, and Environmental Biotechnology and Site Remediation Technology Conference. Colorado Springs, CO, USA, 9-11 Dec 1996, Available from: http://www.osti.gov/bridge/servlets/purl/293384- 0XYmFn/webviewable/293384.pdf. 27 pp (1996) Creedy D P, Garner K, Holloway S, Jones N, Ren T X (2001) Review of underground coal gasification technological advancements. COAL R211 DTI/Pub URN 01/1041. London, UK, Department of Trade and Industry, vp (2001) Creedy D P, Garner K, Oakey J E, Abbott D, Edwards J S, Ren T X, Jie L, Shuqin L, Chai (2004) Clean energy from underground coal gasification in China. COAL R250 DTI/Pub URN 03/1611. London, UK, Department of Trade and Industry, vp (Feb 2004) Curl S J (1979) Underground gasification – reaction zone mapping. ICTIS/TR 06. London, UK, IEA Coal Research. 71 pp (Jun 1979) Daggupati S, Khadse A, Ganesh A, Mahajaniand S, Aghalayam P (2007) Compartment Modeling for Underground Coal Gasification Cavity. International Conference on Advanced Energy Research, 13 Dec 2007, Bombay, India, Indian Institute of Technology. Available from: http://www.ese.iitb.ac.in/~icaer2007/Latest%20PPT%20File/52_225_TS4%20A.pdf, 19 pp (2007) Dantas A (2008) Brazilian geological knowledge. In: Proceedings of PDAC 2008. Toronto, Ontario,

122 IEA Clean Coal Centre Canada, 3 Mar, 2008, Available from: http://www.pdac.com.br/2008/noticia16/agamenon.pdf, 46 pp (2008) Davidson R M (2007) Post-combustion carbon capture from coal fired plants – solvent scrubbing. CCC/125, London, UK, IEA Clean Coal Centre, 58 pp (Jul 2007) Davidson R M (2009) Post combustion carbon capture – solid sorbents and membranes. CCC/144, London, UK, IEA Clean Coal Centre, 64 pp (Jan 2009) Davis B (2009) Personal communication. UCG Process Consultant to Carbon Energy, Australia. [email protected] (8 Mar 2009) Davis B, Mallett C (2009) RM1 to Bloodwood Creek. In: Proceedings of the 4th international underground coal gasification conference. London, UK,10-11 Feb, 2009. Woking, Surrey, UK, The UCG Partnership, 25 pp (2009) de Olivera D P S, Cawthorn R G (1999) Dolerite intrusion morphology at Majuba colliery, northeast Karoo basin, Republic of South Africa. International Journal of Coal Geology. 41; 333-349 (1999) Do T S (2008) Coal bed methane is hot in Vietnam. Available from: http://www.frost.com/prod/servlet/market-insight-top.pag?docid=140182389 2 pp (7 Aug 2008) DTI (2004) Review of the feasibility of underground coal gasification in the UK. DTI/Pub URN 04/1643, Didcot, Oxfordshire, UK, Harwell International Business Centre, 46 pp (Oct 2004) DTI (2005) Directional drilling in coal. DTI/Pub URN 05/657. Technology status report TSR024. Didcot, Oxford, UK, Department of Trade and Industry Cleaner Fossil Fuels Programme. Available from: http://www.berr.gov.uk/files/file20917.pdf, 27 pp (Mar 2005) DTI (2006) Creating the coalmine of the 21st century. The feasibility of UCG under the Firth of Forth. DTI/Pub URN 06/885. Available from: http://www.berr.gov.uk/files/file30689.pdf. Didcot, Oxford, UK, Department of Trade and Industry, Carbon Abatement Technologies Programme. 6 pp (Mar 2006) Dufaux A, Gaveau B, Letolle R, Mostade M, Noel M, Pirard J P (1990) Modelling of the underground coal gasification process at Thulin on the basis of thermodynamic equlibria and isotopic measurements. Fuel. 69, 624-632 (1990) Dvornikova E V, Kreinin (1993) Interaction of subsurface waters with the combustion site during underground coal gasification. Journal of Mining Science. 29, (5); 452-456 (1993) Ecplaza (2009) Linc Energy Limited (ASX:LNC) commences Stage 1 of the UCG project in Vietnam. Available from: http://www.ecplaza.net/news/0/24157/linc_energy_limited_asxlnc.html, 2 pp (20 Apr 2009) Energy Economist (2008) Mining without mines: UCG. Energy economist. 317, 16-18 (Mar 2008) Ergo Exergy (2005) UCG history. Available from: http://www.ergoexergy.com/eUCG_his.htm 1 pp (2005) Feng Chen (2008) The UCG progress in China. In: Proceedings of the 3rd international UCG conference. London, UK, 6 Feb 2008, Underground Coal Gasification Partnership, vp (2008) Feng Chen (2009) Personal communication. UCG Vice Chief Engineer, ENN Science and Technology Co Ltd (17 Jun 2009) Friedmann S J (2006) Congressional hearing on climate change in the Senate Foreign Relations Committee. Underground coal gasification in the USA and abroad. Available from: https://co2.llnl.gov/pdf/UCG_CongTest.pdf, 7 pp (14 Nov 2006) Friedmann S J (2008) Low-cost, zero carbon, H2 production: underground coal gasification with carbon capture and sequestration. Available from: http://www.mountainstateshydrogen.com/ 2008%20Presentations/Friedmann%20-%20UCG_H2_MountainStates_Laramie_July2008.pdf, 21 pp (Jul 2008) Friedmann J, Burton E, Upadhye R (2007a) Carbon management and underground coal gasification. Available from: http://www.purdue.edu/dp/energy/pdfs/CCTR/presentations/CCTR-Dec07- Friedmann.pdf, 30 pp (Dec 2007) Friedmann J, Burton E, Upadhye R (2007b) Underground coal gasification. Paper presented at The Potential for Underground Coal Gasification Meeting. 5 Jun 2007, Washington, DC, USA. Available from: http://www.fossil.energy.gov/international/Publications/cwg_june07_friedman.pdf 18 pp (2007) Friedmann J, Burton E, Kong F-M, Upadhye R, Salari K, Weisgraber T, Buscheck T, Morris J, Goldstein N, Vorobiev O (2008a) Recent advances in UCG technology development. In: Proceedings of the underground coal gasification conference. Houston, TX, USA, 16-17 Jun 2008, Houston, TX, USA, Zeus Development Corporation, 31 pp (2008) Friedmann S J, Upadhye R, Kong F-M (2008b) Prospects for underground coal gasification in a carbon-constrained world. Energy Procedia. 7 pp (2008) Gan Z, Sung M (2008) ENN. Available from: http://www.netl.doe.gov/publications/proceedings/08/CO2E/PDF/session%202/ENN.pdf, 14 pp (2008) GasTech (2007a) GasTech UCG Project, Powder River Basin, Wyoming. In: Proceedings of the 2nd International Conference on Underground Coal Gasification. CD-ROM. 7 Feb 2007, London, UK. Woking, Surrey, UK,The UCG Partnership. 23 pp (2007) GasTech (2007b) Viability of underground coal gasification in the “deep coals” of the Powder River Basin, Wyoming. Casper, Wyoming, GasTech Inc. Available from: http://www.wyomingbusiness.org/pdf/energy/WBC_Report_061507_SPM.pdf ,187 pp (Jun 2007) Gaston B, Franklin T (2009) UCG Central Asia. In: Proceedings of the 4th international underground coal gasification conference. London, UK,10-11 Feb, 2009. Woking, Surrey, UK, The UCG Partnership, 28 pp (2009)

Underground coal gasification 123 Gospodinova T (2008) Personal communication. Promgaz. (12 Dec 2008) Government of India (2007) Status report on underground coal gasification. PSA/2007/1. Available from: http://psa.gov.in/writereaddata/11913281701_ucg.pdf New Delhi, India, Office of the Principal Scientific Adviser, 93 pp (Aug 2007) Granite Island (2009) TDR Tutorial and Riser Bond TDR Product Review. Available from: http://www.tscm.com/riserbond.html, vp (2009) Green M (2008) Underground coal gasification, state of the art. Poland Clean Coal Conference. Bedewo, Poland, 8 Dec 2008. Available from: http://www.kpk.gov.pl/pliki/9343/Michael_Green_08_12_2008.pdf, 25 pp (8 Dec 2008) Green M (2009) Overview of worldwide field activity and the future of UCG. In: Proceedings of the 4th international underground coal gasification conference. London, UK,10-11 Feb, 2009. Woking, Surrey, UK, The UCG Partnership, 33 pp (2009) Green Car Congress (2008) 12 Japan firms to develop underground coal gasification tech. Green Car Congress. Available from: www.greencarcongress.com/2008/06/12-japan-firms-html. 1 pp (17 Jun 2008) Green Car Congress (2009) Alberta to host underground coal gasification demo. Available from: http://www.greencarcongress.com/2009/03/alberta-to-host-underground-coal-gasification-demo-update- on-linc-chinchilla-ucg-in-australia.html 3 pp (18 March 2009) Gregg D W, Hill R W, Olness D U (1976) Overview of the Soviet effort in underground gasification of coal. OSTI ID: 7196456. Livermore, CA, USA, Lawrence Livermore National Laboratory, 58 pp (29 Jan 1976) Gross C, Van der Riet, M (2007) Eskom develops UCG technology project. In: Proceedings of the underground coal gasification conference. Houston, TX, USA, 21 Jun 2007, Houston, TX, USA, Zeus Development Corporation, 13 pp (2007) Halmann M M, Steinberg M (1999) Greenhouse gas carbon dioxide mitigation: science and technology. CRC Press, Taylor & Francis Group, New York, NY, USA, 568 pp (Nov 1998) IEA GHG (2008) Geologic storage of carbon dioxide – staying safely underground. Cheltenham, Gloucestershire, UK, IEA Greenhouse Gas R&D Programme, Available from: http://www.ieagreen.org.uk/glossies/geostoragesfty.pdf, 34 pp (Jan 2008) IPCC (2005) IPCC special report on carbon dioxide capture and storage. Available from: http://arch.rivm.nl/env/int/ipcc/pages_media/SRCCS-final/IPCCSpecialReportonCarbondioxideCapture andStorage.htm, vp (2005) Jackson P (2003) Drilling technologies for underground coal gasification. Paper presented at the DTI international workshop. 1-2 Oct 2003, London, UK, vp (2003) Jones N S, Holloway S, Smith N J P, Browne M A E, Creedy D P, Garner K, Durucan S (2004) UK resource for new exploitation technologies. COAL R271 DTI/Pub URN 04/1879. vp (Nov 2004) Karasevich V (2008) Characteristics and perspectives of new UCG technologies. In: Proceedings of the 3rd international UCG conference. London, UK, 6 Feb 2008, Underground Coal Gasification Partnership, 25 pp (2008) Karaÿ H (2007) Strategic research agenda for Europe. R&D in Polish mining industry. Lulea University of Technology. European Technology Platform on Sustainable Mineral Resources. Available from: http://www.bergforsk.se/presentationer/KGHM_Karas_070524.pdf, 44 pp, (24 May 2007) Kempka T (2009) Personal communication. Project leader. Centre for CO2 storage. Potsdam, Germany (5 Jun 2009) Kempka T, Nakaten N, Azzam R, Schlüter R (2009) Next generation drilling. World Coal. 12, (3); 28-35 (Mar 2009) Ketzer J M, Villwock J A, Caporale G, da Rocha L H, Rockett G, Braum H, Giraffa L (2007) Opportunities for CO2 capture and geological storage in Brazil: the CARBMAP project. In: Proceedings of the Sixth Annual Conference on Carbon Capture & Sequestration, Pittsburgh, PA, USA, 7-10 May, 2007. Available from: http://www.netl.doe.gov/publications/proceedings/07/carbon- seq/data/papers/wed_025.pdf, 25 pp (2007) Khadse A, Mahajani S, Ganesh A, Aghalayam P (2007a) Modelling of underground coal gasification. In: Proceedings of the 2nd international UCG conference. London, UK, 7 Feb 2007, Underground Coal Gasification Partnership, 23 pp (2007) Khadse A, Qayyumi M, Mahajani S, Aghalayam P (2007b) Underground coal gasification: a new clean coal ulilization technique for India. Energy. 32, (11), 2061-2071 (2007) Kolar A J (2008) UCG modeling and simulation. In: UCG workshop, Kabini, Mysore, India, 18-20 Jun 2008. Available from: http://www.cstep.in/presentationsfromspeakers/Presentation_Files/9- UCG_Sim_Mod_Ajit%20Kolar.pdf, 60 pp (2008) Korre A, Durucan S (2008) Coal mineralogy, petrology and coalfield geology. Paper presented at UCGp Training Course, Imperial College, London, UK. 22 Sep 2008. 18 pp (Sep 2008) Kostúr K (2007) The experimental equipment and its automation for underground coal gasification. In: Proceedings of the 16th international symposium on mine planning and equipment selection (MEPS 2007) and the 10th international symposium on environmental issues and waste management in energy and mineral production (SWEMP 2007). CD-ROM. Bangkok, Thailand, 11-13 Dec 2007, Irvine, CA, USA, The Reading Matrix Inc, 506-510 (2007) Kostúr K, Kaïur J (2009) UCG research in Slovakia. In: Proceedings of the 4th international underground coal gasification conference. London, UK,10-11 Feb, 2009. Woking, Surrey, UK, The

124 IEA Clean Coal Centre UCG Partnership, 35 pp (2009) Kostúr K, Blištanová M (2009) The research of underground coal gasification in laboratory conditions. Petroleum & Coal. 51, (1); 1-7 (2009) Krantz W B, Gunn R D (1982) An overview of underground coal gasification – a comparison of modeling studies with field test data. In: Proceedings of the 64th CIC coal symposium. Coal Phoenix of the ‘80s. (Ed: Al Taweel A M). 31 May-3 Jun, 1981, Halifax, Nova Scotia, Canada, Ottawa, Ontario, Canada, Canadian Society for Chemical Engineering. p 468-475 (1982) Kreynin E V (1993) Physical and technological aspects of increasing the efficiency of underground coal gasification. Journal of Mining Science. 29, (N1); 71-74 (1993) Translated from Fiziko- Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No 1 pp 81-85, Jan-Feb, 1993 Kreynin E V (2009) Personal communication. Promgaz, Russia, Chief of Science Technical Centre (11 Feb 2009) Kristiansen A (1996) Understanding coal gasification. IEACR/86, London, UK, IEA Coal Research, 69 pp (Mar 1996) Li Y, Liang X, Liang J (2007) An overview of the Chinese programme on UCG. Data Science Journal. 6, supplement (11 Aug 2007) Slides available from: http://www.codata.org/06conf/presentations/B9/B9-YulanLi.pdf, 26 pp Liang J, Schimada S (2008) Underground coal gasification activities in China. In: Proceedings of the 2008 Pittsburgh coal conference. 30 Sep-2 Oct 2008, Pittsburgh, PA, USA, CD-ROM, Pittsburgh, PA, USA, University of Pittsburgh, 14 pp (2008) Liang J, Liu S, Yu L (1999) Trial study on underground coal gasification of abandoned coal resource. Mining science and technology ‘98. Papers presented at: 1999 international symposium on mining science and technology: 99/SMST. Beijing, China, 29-331 Aug 1999, Rotterdam, Netherlands, Balkema, 854 pp (1999) Liberty Resources (2009) Cleaner. Greener. Safer. Brisbane investor presentation (Syngas). Available from: www.libertyresources.com.au, 19 pp (18 Feb 2009) Linc (2008a) Queensland company promotes cleaner energy in Vietnam. Linc Energy press release. Available from www.lincenergy.com.au, 1 pp (28 Mar 2008) Linc (2008b) Industry Review and an Assessment of the Potential of UCG and UCG Value Added Products. PriceWaterhouseCoopers. Available from: http://www.lincenergy.com.au/pdf/relatedreport- 02.pdf, 53 pp (May 2008) Linc (2008c) Vietnam signs coal gasification deal with foreign partners. Available from: http://www.lincenergy.com.au/pdf/coverage-226.pdf, 1 pp (12 Oct 2008) Linc (2009) Linc Energy’s UCG update. Available from: http://www.lincenergy.com.au/pdf/asx- 139.pdf, 7 pp (10 Mar 2009) Lindblom S R, Smith V E (1993) Rocky Mountain 1 Underground Coal Gasification Test, Hanna, Wyoming, Groundwater Evaluation, Final Report. DOE/MC/25038-3652. June 10, 1988 - June 30, 1993. Available from: http://www.fischer-tropsch.org/DOE/DOE_reports/25038-3652/25038- 3652,%20Part%201,%20Pages%201%20-%20104, %206.04%20MB.pdf, 103 pp (Jun 1993) Liu S (2003) UCG laboratory simulation and studies in China. Paper presented at the DTI international workshop. 1-2 Oct 2003, London, UK, vp (2003) Liu S, Li J-G, Mei M, Dong D-L (2007) Groundwater pollution from coal gasification. Journal of China University of Mining & Technology. 17, (4) 467-472 (2007) Luca Technologies (2009) Technology. Available from: www.lucatechnologies.com 1 pp (2009) Lyman R M, Volkmer J E (2001) Pyrophoricity (spontaneous combustion) of Powder River Basin coals – considerations for coalbed methane development. CR 01-1. Available from: http://www.wsgs.uwyo.edu/Coal/pdf/CR01-1.pdf, Laramie, Wyoming, USA, Wyoming State Geological Survey. 12 pp (Mar 2001) M2M (2008) Underground coal mine methane recovery and use opportunities. Available from: www.methanetomarkets.org, 2 pp (Mar 2008) Mallett C (2006) Managing ground deformation in UCG. Paper presented at the Indo-US Working Group on Coal – Workshop on underground coal gasification. Kolkata, West Bengal, India, 13-14 Nov 2006. Available from: http://fossil.energy.gov/international/Publications/ucg_1106_mallett.pdf, 30 pp (2006) Mallett C (2007) Commercial scale underground coal gasification. Available from: www.carbonenergy.com.au, 34 pp (22 Feb 2007) Mallett C (2008) Carbon Energy’s Bloodwood Creek UCG project. Paper presented at: CoalTech 2008. Brisbane, Qld, Australia, 29-30 Sep 2008. Sydney, NSW, Australia, IIR Pty Ltd. 11 pp (2008) Mallett C, Beath A (2007) Managing environmental impacts associated with large underground coal gasification operations. Paper presented at Petrotech 2007, Delhi, India, 31 pp (15 Jan 2007) Mallett C, Mark R (2007) Underground coal gasification – the logical clean coal option. Paper presented at the WA Energy Summit 2007. Available from: http://carbonenergy.com.au/uploads/File/carbonenergy/presentations/WA%20Energy%20Summit%20 (Perth%20Sept%2020 07).pdf, 22 pp (2007) Mark R (2008) Underground coal gasification – the logical clean coal option. Chinchilla, Qld, Australia, 12-13 Sep 2008. Available from: wdrdc.com.au/downloads/surat-basin-energy- conference/rusty-mark-carbon-energy/download.html 15 pp (Sep 2008) Mark R, Mallett C (2008) Wyoming UCG trials at Hanna. A template for commercial scale UCG in Queensland. In: Proceedings of the conference on clean coal technologies Queensland and Wyoming –

Underground coal gasification 125 the case for cooperation. Brisbane, Qld, Australia, 10-11 Apr 2008, Brisbane, Qld, Australia, University of Queensland, 14 pp (2008) Mastalerz M, Drobniak A, Rupp J, Shafirovich E, Varma A (2008) The potential for underground coal gasification in Indiana. Phase II report to the Indiana Center for Coal Technology Research, West Lafayette, IN, USA, Purdue University. Available from: www.purdue.edu/dp/energy/pdfs/CCTR/researchReports/IGS-PhaseIIReport_Dec08.pdf 27 pp (Nov 2008) Mayne D (2009) Personal communication. (26 Feb 2009) Minotti M (2009) Personal communication. Project Manager, Linc Carbon Solutions, Chinchilla, Queensland, Australia (26 May 2009) Moncarz P D (2008) Underground Coal Processing. Polish – US Made Radical Energy Solution Technologies. Pilot Plant in Rybnik. Paper presented at: Clean Coal Technology Conference, Krakow/Katowice, Poland, 17-18 March, 2008. Available from: http://www.kpk.gov.pl/pliki/8263/ Piotr%20Moncarz.pdf, 42 pp (2008) Morzenti S (2008) UCG in the “Deep Coals”of the Powder River Basin, Wyoming Progress 2007-2008. In: Proceedings of the underground coal gasification conference. 21-22 Jun 2008. Houston, TX, USA, Zeus Development. 42 pp (2008) Morzenti S (2009) Personal communication. President, GasTech Inc, Casper, WY, USA (11 Jun 2009) Nandakumar K (2006) UCG and power generation – BHEL’s role. Available from: http://www.fossil.energy.gov/international/Publications/cwg_april06_ucg_bhel.pdf, 16 pp (Apr 2006) Nelson G R, Mueller M G, Palmer F D (2008) The urgency of sustainable coal. Washington DC, USA, The National Coal Council. Library of Congress Control Number 2008928663. Available from: http://www.nationalcoalcouncil.org/Documents/NCC_REPORT_2008.pdf, 197 pp (May 2008) Nordic (2009) Nordic Oil and Gas to submit application for underground coal gasification project. Available from: http://www.nordicoilandgas.com/july209.html, 1 pp (2 Jul 2009) NorthAm Oil (2008) Swan Hills Synfuels plans coal gasification project. NorthAm Oil. 20, 12 (10 Sep 2008) NTPC (2006) Economics of power generation with UCG. Available from: http://www.fossil.energy.gov/international/Publications/ucg_1106_ntpc.pdf, 67 pp (Nov 2006) Ökten G, Didari, V (1994) Underground gasification of coal. Coal. Resources, properties, utilization, pollution. (Ed: Kural O). Istanbul, Turkey, Mining Faculty, Istanbul Technical University. p 371-378 (1994) Olness D U (1981) The Podmoskovnaya underground coal gasification station. OSTI ID: 6152202; DE81030632. UCRL-53144. Livermore, CA, USA, Lawrence Livermore National Laboratory, 81 pp (15 May 1981) Olness D, Gregg D W (1977) Historical development of underground coal gasification. UCRL-52283. OSTI ID: 7284583. Lawrrence Livermore Laboratory, Livermore, CA, USA, Available from: http://www.osti.gov/bridge/servlets/purl/7284583-Fb1MIt/ 62 pp (1977) Palarski J (2007) Polish activities in underground coal gasification. Paper presented at: Society of Mining Professors, 18th annual general meeting. Belgrade, Jun 2007, Available from: http://www.mineprofs.org/info/research/SOMP-07-Research-Palarski.pdf, 30 pp (2007) Pearce S (2008) Maximising the potential for ␧UCG by leveraging core mining competencies. In: Proceedings of the underground coal gasification conference. 21-22 Jun 2008. Houston, TX, USA, Zeus Development. 42 pp (2008) Perkins G (2004) Coupling dominant surface submodels and complex physical process Computational Fluid Dynamics. Australian Mathematical Society Journal ANZIAM. Available from: http://anziamj.austms.org.au/V45/CTAC2003/Perk/Perk.pdf, 45, C817-830, 14 pp (2004) Perkins G M P (2005) Mathematical modelling of underground coal gasification. PhD Doctorate Thesis. Available from: http://handle.unsw.edu.au/1959.4/25518. Sydney, NSW, Australia, Materials Science & Engineering, University of New South Wales. vp (Dec 2005) Perkins G, Saghafi A, Sahajwalla V (2003) Numerical modelling of underground coal gasification and its application to Australian coal seam conditions. Available from: http://barossa.ac3.edu.au/edu/papers/perkinsg01.pdf, 12 pp (2003) Perkins G, Sahajwalla V (2006) A numerical study of the effects of operating conditions and coal properties on cavity growth in underground coal gasification. Energy & Fuels, 20, 596-608 (2006) Puri R (2006) UCG syngas: product options and technologies. In: Proceedings of the underground gasification workshop. Kolkata, India, 12-15 Nov 2006. Available from: http://www.fe.doe.gov/international/Publications/ucg_1106_bp.pdf, 16 pp (2006) Red Orbit (2007) China begins building first industrial underground coal gasification project. Red Orbit. Available from: http://www.redorbit.com/news/business/973181/china_begins_building_first_industrial_underground_coal _gasification_project/index.html, 1 pp (19 Jun 2007) Reuters (2008) Altona Resources PLC – Field Programme Completion. Available from: http://www.reuters.com/article/pressRelease/idUS72604+04-Mar-2008+RNS20080304, 3 pp (4 Mar 2008) Rippon J (2009) Personal communication. Consultant geologist. (17 Feb 2009) Rogut J (2008) Review of European and Russian UCG. In: Proceedings of the 3rd international UCG conference. London, UK, 6 Feb 2008, Underground Coal Gasification Partnership, 32 pp (2008) Rogut J, Steen M (2008) Hydrogen oriented underground gasification of coal. In: Proceedings of the

126 IEA Clean Coal Centre 2008 Pittsburgh coal conference. 30 Sep-2 Oct 2008, Pittsburgh, PA, USA, CD-ROM, Pittsburgh, PA, USA, University of Pittsburgh, 8 pp (2008) Rogut J, Steen M, de Santi G, Dubinski J (2008) Technological, environmental and regulatory issues relating to CCS and UCG. In: Proceedings of the Clean Coal Technology Conference: geological aspects of underground storage and processing. Cracow-Katowice, Poland, 17-18 Mar 2008. Available from: http://www.kpk.gov.pl/pliki/8262/Marc%20Steen.pdf, 17 pp (2008) Saghafi A (2001) Coal seam gas reservoir characterisation. Paper presented at: Gas from coal symposium. 27 Mar 2001, Brisbane, Qld, Australia. Available from: http://www.australiancoal.csiro.au/ pdfs/saghafi.pdf 14 pp (2001) Sallans P (2009) Personal communication. Manager, Unconventional Energy, Mitchell Energy Group, Toowong, Qld, Australia (25 Mar 2009) Sapex (2007) SAPEX announces an initial inferred coal resource estimate for Arckaringa project. Available from: http://www.sapex.com.au/asx/07-06-28_SAPEX_announces_initial_JORC_coal_ figures.pdf, 6 pp (28 Jun 2007) Shackley S, Reiche A, Mander S (2004) The public perceptions of underground coal gasification (UCG): a pilot study. Working paper 57. Manchester, UK,Tyndall Centre for Climate Change. Available from: http://www.tyndall.ac.uk/publications/working_papers/wp57.pdf, 51 pp (Aug 2004) Shafirovich E, Mastalerz M, Rupp J, Varma A (2008a) The potential for underground coal gasification in Indiana. Phase 1 report. Text version. Discovery Park Energy Centre. Purdue University, IN, USA. Available from: http://www.purdue.edu/dp/energy/pdfs/CCTR/researchReports/UCG-Phase1- 08-31-08.pdf, (31 Aug 2008) Shafirovich E, Varma A, Rupp J, Mastalerz M (2008a) The potential for underground coal gasification in Indiana. Presentation at CCTR Advisory Panel Meeting, 5 Jun, 2008, Purdue University, Indianapolis, IN, USA, Available from: http://www.purdue.edu/dp/energy/pdfs/CCTR/presentations/Shafirovich-CCTR-June08.pdf, 14 pp (5 Jun 2008) Shafirovich E, Mastalerz M, Rupp J, Varma A (2008b) The potential for underground coal gasification in Indiana. Phase 1 report to CCTR. Slide presentation. Discovery Park Energy Centre. Purdue University, IN, USA. Available from: http://www.purdue.edu/dp/energy/pdfs/CCTR/ presentations/UCG-09-16-08.pdf, (16 Sep 2008) Shafirovich E, Varma A, Mastalerz M, Drobniak A, Rupp J (2008c) The potential for underground coal gasification in Indiana. Presentation at CCTR Advisory Panel Meeting, 11 Dec, 2008, Purdue University, Indianapolis, IN, USA. Available from: http://www.purdue.edu/dp/energy/events/CCTR_Meetings_Dec_2008/presentations/Varma-12-11- 08.pdf, 27 pp (11 Dec 2008) Shafirovich E, Varma A, Mastalerz M, Drobniak A, Rupp J (2009) The potential for underground coal gasification in Indiana. Final report to the Indiana Center for Coal Technology Research (CCTR). Available from: www.purdue.edu/discoverypark/energy/pdfs/cctr/researchReports/UCG-FinalReport-03- 02-09.pdf, 51 pp (Mar 2009) Sherwood A (2009) Personal communication. Senior Geologist, Crown Minerals, Ministry of Economic Development, Wellington, New Zealand (4 Feb 2009) Shimada S, Ogha K, Tamari A, Ishii E (1996) Cost estimation of underground coal gasification in Japan. Mineral Resources Engineering. 5, (3); 241-252 (1996) Singareni Collieries (2007) Exploration Division. Godavari Valley coal. Available from: http://scclmines.com/downloads/exploration.pdf, 15 pp (2007) Singh A K (2006) Underground coal gasification in India. In: Proceedings of the underground gasification workshop. Kolkata, India, 12-15 Nov 2006. Available from: www.fossil.energy.gov/international/International_Partners/November_2006_UCG_Meeting.html 35 pp (2006) Singleton A H, Pilcher R C (2007) The commercialization of ISE’s steeply dipping bed UCG technology. In: Proceedings of the 2nd International Conference on Underground Coal Gasification. CD-ROM. 7 Feb 2007, London, UK. Woking, Surrey, UK, The UCG Partnership. 18 pp (2007) Sloss L L (2005) Coalbed methane emissions – capture and utilisation. CCC/104. London, UK, IEA Clean Coal Centre, 56 pp (Nov 2005) Smith I M (2009) Gas turbine technology for syngas/hydrogen in coal-based IGCC. IEA/CCC 155, London, UK, IEA Clean Coal Centre, vp (Sep 2009) Srinivas S, Khadse A, Aghalayam P, Ganesh A, Malik R K, Mahajani S M (2007) Fischer-Tropsch synthesis of the UCG product gas. In: Proceedings of the 24th annual international Pittsburgh coal conference. Johannesburgh, South Africa, 10-14 Sep 2007, CD-ROM, Pittsburgh, PA, USA, University of Pittsburgh, 12 pp (2007) Stephens D R, Hill R W, Borg I Y (1985) Underground coal gasification review. UCRL-92068; CONF-850427-2. Presented at: Western fuels symposium. 24 Apr 1984, Grand Junction, CO, USA. 13 pp (1985) Stockwatch (2009) Carbon Energy Limited (ASX:CNX) signs agreement with ZeroGen for Australia's first demonstration of UCG and CCS technology. Available from: http://www.stockwatch.com/ newsit/newsit_newsit.aspx?bid=U-ab61081-U:CNXAF-20090721&symbol=CNXAF&news_region=U, 3 pp (21 Jul 2009) Sury M, White M, Kirton J, Carr P, Woodbridge R, Mostade M, Chappell R, Hartwell D, Hunt D, Rendell N (2004a) Review of environmental issues of underground gasification. COAL R272 DTI/Pub

Underground coal gasification 127 URN 04/1880. Didcot, Oxfordshire, UK, Harwell International Business Centre, vp (Nov 2004) Sury M, White M, Kirton J, Carr P, Woodbridge R, Mostade M, Chappell R, Hartwell D, Hunt D, Rendell N (2004b) Review of environmental issues of underground gasification. Best practice guide. COAL R273 DTI/Pub URN 04/1881. Didcot, Oxfordshire, UK, Harwell International Business Centre, vp (Nov 2004) Syngas Refining (2008a) Linc Energy produces first Chinchilla GTL liquids. Zeus Syngas Refining Report. 24 (16 Oct 2008) Syngas Refining (2008b) Linc moving Chinchilla UCG/GTL project south. Zeus Syngas Refining Report. IV, (21); 13-14 (24 Nov 2008) Syngas Refining (2008c) Linc Energy extending BP’s Australian UCTL fuel option. Zeus Syngas Refining Report. IV, (23); 14-17 (22 Dec 2008) Syngas Refining (2009a) Worldwide underground coal gasification plants & projects. Zeus Syngas Refining Report. V, (10); 9-10 (21 May 2009) Syngas Refining (2009b) Carbon Energy raises capital to advance UCG projects. Zeus Syngas Refining Report. News Update (8 Jun 2009) Syngas Refining (2009c) Canadian deep UCG project producing product gas this month. Zeus Syngas Refining Report. V, (11); 8 (8 Jun 2009) Teel G (2009) Alberta to be site of $30-million experiment to turn underground coal into syngas. Calgary Herald. Available from: http://www.calgaryherald.com/Technology/Alberta+site+million+experiment+turn+underground+coal+ into+syngas/1399356/story.html 3 pp (17 Mar 2009) The Australian (2008) Clash over gas on the plains of western Darling Downs. The Australian. Available from: http://www.theaustralian.news.com.au/story/0,25197,24150163-5005200,00.html 2 pp (9 Aug 2008) Thompson P N, Mann J R, Williams F (1976) Underground gasification of coal. London, UK, National Coal Board, 72 pp (1976) Thorsness C B, Britten J A (1989) Lawrence Livermore National Laboratory underground coal gasification project: final report. UCID-21853. Livermore, CA, USA, Lawrence Livermore National Laboratory. vp (15 Oct 1989) Tillman T (2008) TEXYN’s “Santa Barbara” mining system. In: Proceedings of the 2008 Pittsburgh coal conference. 30 Sep-2 Oct 2008, Pittsburgh, PA, USA, CD-ROM, Pittsburgh, PA, USA, University of Pittsburgh, 20 pp (2008) Tobol (2009) Development of Chernigovskoye deposit with subsequent coal gasification. Available from: http://92.47.47.154/index.php?part=project_full&project=102&pageid=500013, 1 pp (2009) Turner M (2009) Personal communication. Senior Geologist, Clean Coal Ltd, London, UK Turner M, Brabham P, Griffiths A, Marsh R, Sapsford D, Williams K (2009) The potential for underground coal gasification in Wales. In: Proceedings of the 4th international underground coal gasification conference. London, UK,10-11 Feb, 2009. Woking, Surrey, UK, The UCG Partnership, 34 pp (2009) Upadhye R, Burton E, Freidmann J (2006) Underground coal gasification: science and technology gaps. Available from: http://www.fe.doe.gov/international/Publications/ucg_1106_llnl_upadhye.pdf, Livermore, CA, USA, Lawrence Livermore National Laboratory, 30 pp (14 Nov 2006) US DOE (1989) Rocky Mountain 1. Underground coal gasification test, Hanna, Wyoming. Summary report. Prepared by the United Engineers & Constructors Inc. Stearns-Roger Division for the US Department of Energy. vp (Mar 1989) US DOE (1997) Environmental assessment. Hoe Creek underground gasification test site remediation. DOE/EA-1219. Available from: http://www.osti.gov/bridge/servlets/purl/555289-cbOfnH/webviewable/ 121 pp (Oct 1997) USGS (2008) Common water measurements. Reston, VA, USA, United States Geological Service. Available from: http://ga.water.usgs.gov/edu/characteristics.html#pH vp (7 Nov 2008) US-India WG (2006) Third US-India working group meeting on coal. Clean coal technology. Available from: http://www.fe.doe.gov/international/Publications/cwg_april06_cbm_neyveli.pdf, 21 pp (2006) Van der Riet (2008) Underground coal gasification. Energize. 40-43 (Mar 2008) Van der Riet (2009) Personal communication. Manager. Eskom UCG Project at Majuba. (25 Jun 2009) Van der Riet M, Beeslaar M, Gross C, Blinderman M (2008) Progress on Eskom’s Majuba underground coal gasification project. In: Proceedings of the underground coal gasification conference. Houston, TX, USA, 61-17 Jul 2008, Houston, TX, USA, Zeus Development Corporation, 13 pp (2008) Vasyuchkov Y F, Vorobjev B M, Vasioutchkov K (1998) Unconventional mining technologies for clean and efficient power generation. Mining Engineering. 65-69 (Apr 1998) Veber I (2003) Feasibility study of UCG in Velenje, Slovenia. Paper presented at the DTI international workshop. 1-2 Oct 2003, London, UK, vp (2003) Veber I, Dervariè E (2004) Reserves presentation for Velenje colliery according to United nations framework classification. Paper presented at the First Session of UNECE Ad Hoc Group of Experts on Supply of Fossil Fuels, Geneva, Switzerland, 10-11 Nov 2004, Available from: http://www.unece.org/energy/se/pdfs/adclass/day2/Subelj_Veber_UNFC.pdf, 43 pp (2004) VNBusinessNews (2009) Gazprom to supply coal gasification technology to Vietnam Vietnam Business Finance. Available from: http://www.vnbusinessnews.com/2009/05/gazprom-to-supply-coal-

128 IEA Clean Coal Centre gasification.html, 1 pp (15 May 2009) WA Business News (2008) Altera Resources changes focus to UCG. WA Business News, 1 pp (28 Aug 2008) Walker L K (2007) Commercial development of underground coal gasification. Proceedings of he Institution of Civil Engineers. Energy 160. Paper 700010. Issue EN4. 175-180 (Nov 2007) Walker S (2000) Major coalfields of the world. CCC/32. London, UK, IEA Clean Coal Centre, 131 pp (Jun 2000) Walker L (2008) The development and future of underground coal gasification in the Asian region. In: Proceedings of the underground coal gasification conference. Houston 21-22 Jun 2008. Houston, TX, USA, Zeus Development. 14 pp (2008) Walters S (2009) UCG – getting the most out of coal. Energy World. 372, 16-17 (Jun 2009) Wilcox B (2008) Underground coal gasification: the missing piece in the world’s energy puzzle. In: Proceedings of the underground coal gasification conference. Houston, TX, USA, 21-22 Jun 2008. Houston, TX, USA, Zeus Development. 50 pp (2008) Wilks I H C (1983) The cavity produced by gasified thin deep seams. In: Proceedings of the 9th underground coal gasification symposium. US DOE Report DOE/METC/84-7; 314-322 (1983) Winning D (2008) Chinese plant to rely on underground coal gasification. Dow Jones. Available from: http://www.downstreamtoday.com/(S(df0y3x45j1wazz45dukdkc45))/news/ArticlePrint.aspx?aid=11150 &AspxAutoDetectCookieSupport=1, 2 pp (2 Jun 2008) World Energy Council (2001) 2001 Survey of Energy Resources. (Eds Clarke A W, Trinnaman J A), London, UK, World Energy Council, CD-ROM (2001) World Energy Council (2004) 2004 Survey of Energy Resources. London, UK, World Energy Council. Available from: http://www.worldenergy.org/documents/ser2004.pdf, 464 pp (2004) World Energy Council (2007) 2007 Survey of Energy Resources. London, UK, World Energy Council. Available from: http://www.worldenergy.org/documents/ser2007_final_online_version.pdf, 600 pp (2007) Yang L (2003) Study on the method of two-phase underground coal gasification with unfixed pumping points. Energy Sources. 25, (9); 917-930 (Sep 2003) Yang L (2004) Study on the model experiment and numerical simulation for underground coal gasification. Fuel. 83, 57584 (2004) Yang L, Liu S, Yu L, Liang J (2007) Experimental study of shaftless underground gasification in thin high-angle coal seams. Energy & Fuels. 21, (4); 2390-2397 (2007) Zancan F L, Cunha P (2007) RDID&D perspectives towards climatechangeless coal technologies in Brazil. In: Proceedings of the third international conference on clean coal technologies for our future. 15-17 May 2007, Cagliari, Sardinia, Italy. London, UK, IEA Clean Coal Centre, vp (2007) Zanuz M (2009) Personal communication. (17 Mar 2009) Zapušek A (2008) Personal communication. (19 Nov 2008) Zavšek S (2008) Personal communication. (24 Nov 2008) Zieleniewski M, Brent A C (2008) Evaluating the achievable benefits of extending technologies for uneconomical coal resources in South Africa. In: Proceedings of the 2008 Pittsburgh coal conference. 30 Sep-2 Oct 2008, Pittsburgh, PA, USA, CD-ROM, Pittsburgh, PA, USA, University of Pittsburgh, 15 pp (2008) Zorya A Y, Kreynin E V, Sushentsova B Y (2009) What is necessary for transformation of a UCG enterprise into highefficient, stable and economically effective industrial production? In: Proceedings of the 4th international underground coal gasification conference. London, UK,10-11 Feb, 2009. Woking, Surrey, UK, The UCG Partnership, 31 pp (2009)

Underground coal gasification 129