Uk Coal Resource for New Exploitation Technologies
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UK COAL RESOURCE FOR NEW EXPLOITATION TECHNOLOGIES Report No. COAL R271 DTI/Pub URN 04/1879 November 2004 by N S Jones, S Holloway, D P Creedy and S Durucan N J P Smith and K Garner M A E Browne British Geological Survey Wardell Armstrong Imperial College Kingsley Dunham Centre Lancaster Building Department of Environmental Keyworth High street Science and Technology Nottingham Newcastle-u- Lyme South Kensington Campus NG12 5GG ST5 1PQ London United Kingdom United Kingdom SW7 2AZ United Kingdom Tel: +44 (0)115 9363100 Tel: +44(0)1782 612626 Tel: +44 (0)20 7594 7354 The work described in this report was carried out under contract as part of the DTI Cleaner Coal Technology Transfer Programme. The programme is managed by Future Energy Solutions. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of the DTI or Future Energy Solutions First published 2004 © Crown copyright 2004 iii iv EXECUTIVE SUMMARY This focus of this report are the UK coal resources available for exploitation by the new technologies of Underground Coal Gasification, Coalbed Methane production and Carbon Dioxide Sequestration. It also briefly considers the potential for further underground and opencast mining and the extraction of methane from working and closed mines. The potential for mining was mainly considered because it has a bearing on the scope for the new exploitation technologies rather than to identify resources or potential mine development areas. The report covers the UK landward area and nearshore areas, although information on the extent of underground mining was not available for the nearshore areas. This work was carried out by the British Geological Survey, with the assistance of Wardell Armstrong and Imperial College, London. It represents a summary of the results of the Study of the UK Coal Resource for New Exploitation Technologies Project, carried out for the DTI Cleaner Coal Technology Programme (Contract No. C/01/00301/00/00) under the management of Future Energy Solutions (Agreement No. C/01/00301/00/00). Coalbed methane production can be subdivided into three categories: Methane drained from working mines, known as Coal Mine Methane (CMM), has been exploited in the UK since at least the 1950s. Currently all working mines except Daw Mill and Ellington drain methane. It is used to generate electricity at Harworth, Tower and Thoresby collieries and in boilers at Welbeck, Kellingley and Ricall/Whitemoor collieries. There is potential to increase the exploitation of CMM in the UK but this is mainly a question of economics. There is also an environmental case for further utilisation, as methane is an important greenhouse gas, 23 times more powerful than carbon dioxide on a mass basis. Methane drained from abandoned mines, known as Abandoned Mine Methane (AMM), is a methane-rich gas that is obtained from abandoned mines by applying suction to the workings. The fuel gas component consists primarily of methane desorbed from seams surrounding the mined seam(s). These unmined seams have been de-stressed and fractured by the collapse of overlying and underlying strata into the void left by the extracted seam(s). Currently AMM is being exploited at sites in North Staffordshire (Silverdale Colliery), the East Midlands (Bentinck, Shirebrook and Markham collieries) and Yorkshire (Hickleton, Monk Bretton and Wheldale collieries). The methane-rich gas is used for electricity generation or supplied to local industry for use in boilers and kilns. Over the last few years, the fledgling UK AMM industry has started to ascend a learning curve. However, it has suffered a major setback since the wholesale price of electricity fell under the New Electricity Page v Trading Arrangements and AMM does not currently qualify as renewable energy in the UK. Coalbed methane produced via boreholes from virgin coal seams, known as Virgin Coalbed Methane (VCBM), has been the subject of significant exploration effort in Lancashire, North Wales, South Wales and Scotland. The best production of gas and water from a single well is understood to be from the project at Airth, north of Falkirk in Scotland. However, this is not economic at present. The main reason for the slow development of VCBM in the UK is perceived to be the widespread low permeability of UK coal seams, although little work has been carried out in the UK on coal permeability, or to truly identify the reasons for the lack of success. This must be overcome before the otherwise significant resource bases in the Clackmannan Syncline, Canonbie, Cumbria, South Lancashire, North Wales, North Staffordshire and South Wales coalfields can be exploited. A technological breakthrough is required to overcome the likely widespread low permeability in the UK Carboniferous coal seams. Otherwise, at best, production will probably be limited to niche opportunities in areas where high seam permeability exists. The criteria used to define and map the location of VCBM resources are as follows: • Coal seams greater than 0.4m in thickness at depths >200m • Seam gas content >1m3/tonne • 500 metres or more horizontal separation from underground coal workings • Vertical separation of 150m above and 40m below a previously worked seam • Vertical separation of >100m from major aquifers, and • Vertical separation of >100m from major unconformities Areas with a CMM resource (current underground coal mining licences) were excluded. Note that the presence of a CBM resource does not imply permeability in the coal seams or that the resource can be recovered economically now or at any time in the future. Using these criteria resource areas were defined and represented on the maps. The total VCBM resource of these areas is thought to be about 2,900 x 109m3 (about 29 years of UK natural gas consumption). Underground coal gasification (UCG) is the process whereby the injection of oxygen and steam/water via a borehole results in the partial in-situ combustion of coal to produce a combustible gas mixture consisting of CO2, CH4, H2 and CO, the proportions depending on temperature, pressure conditions and the reactant gases injected. This product gas is then extracted via a producing well for use as an energy source. All previous trials of this technology in the UK took place in the 1950’s or before, eg Durham (1912), Newman Spinney (1949-1956) and Bayton (c.1955), although this country is well placed for UCG, with large reserves of indigenous coal Page vi both onshore and offshore. The main criteria used for the delineation and mapping of resource areas with potential for UCG were: • Seams of 2m thickness or greater • Seams at depths between 600 and 1200m from the surface • 500m or more horizontal and vertical separation from underground coal workings and current coal mining licences, and • Greater than 100m from major aquifers While seams outside these depth and thicknesses criteria are known to support UCG, the criteria were chosen for this generic study on economic and environmental grounds as described later in this report. The establishment of these criteria do not rule out UCG projects in shallower or thinner seams, if local site specific factors support it. Mapping of the potential UCG resource has identified large areas suitable for UCG, particularly in Eastern England, Midland Valley of Scotland, North Wales, Cheshire Basin, South Lancashire, Canonbie, the Midlands and Warwickshire. Potential also exists in other coalfields but on a smaller scale; this is often limited by the extent of former underground coal mining activities. The total area where coals are suitable for gasification is approximately 2.8 x 109m2. Where the criteria for UCG are met, the minimum volume of coal available for gasification, calculated assuming only one 2m thick seam meets the criteria across each area, is approximately 5,698 x 106m3 (~7Btonnes). Using an average of the total thickness of coals that meet the criteria across each area gives a more realistic resource figure of 12,911 x 106m3 (~17Btonnes). Carbon dioxide (CO2) sequestration onto coal is a technology that has been proposed as a greenhouse gas mitigation option. Carbon dioxide has an affinity to be adsorbed onto coal and this affinity is greater than that of methane. Thus it has been proposed that CO2 could be used to enhance coalbed methane production by displacing the methane from sorption sites on coal. Furthermore, nitrogen has the potential to enhance coalbed methane production, by lowering the partial pressure of methane in the cleat and causing methane to desorb faster from the sorption sites as well as sweeping the gases from the natural coal fracture system. Thus it may be possible to enhance coalbed methane production using flue gas (essentially a mixture of nitrogen and CO2) and thus bypass the expensive step of separating the CO2 from flue gases. If the main objective, however, is CO2 sequestration rather than methane production then separation of the flue gases may be worthwhile. This technology is at a very early stage of development. A trial has been conducted in the San Juan Basin, USA, but the results were inconclusive as, from a research Page vii perspective, the trial was brought to an end prematurely. Further research programmes are under way, but conclusive results are not yet available. However, any CO2 sequestration project that relies on injecting CO2 into coal seams will require significant coal seam permeability and this appears to be a major issue in the UK (see VCBM above). Furthermore, if there was a requirement for permanent sequestration of CO2 on coal seams, this would render them unminable and ungasifiable (because the CO2 would be released). Any future mining of such coals would require re-capture and sequestration of the stored CO2. Because of the major uncertainties surrounding this technology, no areas specifically suitable for it have been identified.