A preliminary evaluation of sources of geothermal energy for direct heat use

A. G. Reyes

GNS Science Report 2007/16 July 2007

GNS Science

BIBLIOGRAPHIC REFERENCE

Reyes, A. G., 2007. A preliminary evaluation of sources of geothermal energy for direct heat use, GNS Science Report 2007/16, 42 p.

A. G. Reyes, GNS Science, PO Box 30368, Lower Hutt

© Institute of Geological and Nuclear Sciences Limited, 2007 ISSN 1177-2425 ISBN 978-0-478-09980-5

CONTENTS

ABSTRACT...... iii KEYWORDS ...... iii 1.0 SOURCES OF GEOTHERMAL ENERGY FOR DIRECT USE ...... 1 2.0 PRESENT DIRECT HEAT USE FROM GEOTHERMAL SOURCES ...... 2 3.0 CONVENTIONAL SOURCES OF GEOTHERMAL ENERGY...... 4 3.1 Hot springs ...... 4 3.2 Cascade and parallel uses from operating geothermal systems ...... 5 3.2.1 Cascade uses...... 5 3.2.2 Parallel uses...... 6 4.0 UNCONVENTIONAL SOURCES OF GEOTHERMAL ENERGY...... 8 4.1 Introduction...... 8 4.2 Conductive heat flow ...... 9 4.2.1 Heat Reserves in Dry Rock at Shallow Depths (<250m) ...... 14 4.2.2 Heat Reserves in Dry Rock at 120oC ...... 14 4.2.3 Heated Water in Abandoned Hydrocarbon Wells ...... 15 4.2.4 Heated Water in Abandoned Underground Mines ...... 18 5.0 PROJECTED USE OF UNCONVENTIONAL GEOTHERMAL RESOURCES ...... 20 5.1 Shallow conductive heat flow and ground source heat pumps ...... 20 5.2 Abandoned hydrocarbon wells ...... 20 5.3 Abandoned underground mines...... 20 6.0 SUMMARY AND CONCLUSIONS ...... 20 7.0 REFERENCES ...... 25

FIGURES

Figure 1 Conventional and unconventional sources of geothermal energy in New Zealand for direct use and power generation and their general temperatures, source depths, permeability, heat grade and presence of circulating fluids. ORC= Organic Rankine Cycle, NE= Natural Energy engine...... 1 Figure 2 Drect heat uses in various hot spring systems of New Zealand (data from White, 2006)...... 3 Figure 3 Direct heat uses in terms of relative percentage of extracted energy (data from White, 2006)...... 3 Figure 4 Hot spring system locations and direct heat usage in New Zealand...... 4 Figure 5 Cascade use of waste water for prawn farming in Wairakei. The power plant is on the left and the prawn farm on the right...... 5 Figure 6 Two cascade options for an agri-business complex using 130oC wastewater in Wairakei. Total energy usage for each process is roughly estimated and assumptions are shown above...... 6 Figure 7 Conductive heat flow map of New Zealand (Allis et al, 1998)...... 10 Figure 8 Map showing areas under the jurisdiction of the Department of Conservation (blue), regions with thermal gradient >33oC/km (yellow), <33oC/km (outside yellow regions), the TVZ, Coromandel and Northland...... 11 Figure 9 Geothermal areas in the TVZ (from Bibby et al, 1995)...... 12 Figure 10 Estimated constant temperatures at 250m depth...... 13

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Figure 11 Location of onshore abandoned oil and gas wells...... 16 Figure 12 Potential uses of heat from abandoned hydrocarbon wells...... 17 Figure 13 Location of flooded abandoned underground coal and mineral mines, used in calculating the available low-grade heat from flood waters in mine caverns...... 18 Figure 14 Map of New Zealand showing the conductive heat flow contours (Allis et al, 1998)), hot spring systems and their discharge temperatures in the TVZ, Ngawha and areas outside these two, abandoned hydrocarbon wells and the location of some underground coal and gold or copper mines...... 22 Figure 15 Potential energy from conventional and unconventional sources of heat in New Zealand. *Does not include the edges of geothermal systems in the TVZ...... 23

TABLES

Table 1 Conservative projected energy use, in megawatts thermal (MWt) and petajoules (PJ), of parallel direct heat usage in power-producing geothermal systems...... 7 Table 2 Specific heat capacity and bulk density values of andesite, greywacke and water. Greywacke density data is from Malengreau et al (2000), upper value for andesite from Johnson and Olhoeft (1984). The heat capacity of greywacke is that of sandstone (www.edumine.com) and the heat capacity of granite (www.EngineeringToolbox.com) at 27oC and 100 kPa is used as a proxy for andesite. Water constants are from Weast et al (1989)...... 9 Table 3 Areas with thermal gradients of 21-33oC and >33oC outside environmentally- and socio-politically- sensitive regions administered by the Department of Conservation, shown in Figure 8. The total area of New Zealand is 264,787 km2. Percentages are with respect to total land area...... 12 Table 4 Estimate of heat reserves from 250m for ground source heat pump use. In the calculation, porosity is arbitrarily set at 0.01, the thermal gradient used for low thermal gradient regions is 28oC/km, 50oC/km for the TVZ, 40oC/km for Coromandel and Ngawha Northland and 33oC/km for the rest of the North Island and parts of the South Island. C= heat capacity, ρ= density; initial temperature = 15oC; recovery factor = 1%...... 14 Table 5 Estimate of heat reserves from depths where temperatures are about 120oC. In the calculation, porosity is 0.01, the thermal gradients used for the different regions are the same as in Table 4...... 15 Table 6 Extractable heat energy from warm waters in abandoned underground mines...... 19 Table 7 Present and potential extractable energy from geothermal systems in New Zealand for direct heat use. See calculations in appendices. GSHP= ground source heat pump...... 21

APPENDICES

Appendix 1 Waste water and steam from power generating geothermal systems in the TVZ (cascade and parallel uses) ...... 27 Appendix 2 Warm grounds and waters at edges of high-temperature geothermal systems in the TVZ...... 29 Appendix 3 Abandoned Hydrocarbon wells ...... 30

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ABSTRACT

New Zealand is one big geothermal system with pockets of subsurface high temperatures where heat can be mined economically, from fluids and/or rock. Exploitable temperatures range from as low as <10oC to as high as >350oC. Depths of heat extraction vary from about 15m to >5000m. Conventional sources of geothermal energy with high grade heat reserves include high enthalpy geothermal systems in the Taupo Volcanic Zone (TVZ) and Ngawha and hot spring systems outside the TVZ. About 265 PJ of energy can be extracted from conventional sources of geothermal energy such as hot springs and hot waters discharged from power plants or from wells used expressly for direct heat use from high enthalpy geothermal systems in the TVZ and Ngawha. Only 5% of energy is being used at present at about 14.2 PJ. There are, however, a wide range of unconventional sources of geothermal energy from low to high grade heat reserves that have hardly been exploited including edges of high-enthalpy geothermal systems in the TVZ and Ngawha, warm to hot water in abandoned hydrocarbon wells and underground flooded coal and mineral mines, and the natural conductive heat in sedimentary basins and igneous terrain. At relatively shallow depths from 15m to about 250m, where temperatures remain constant at about 15o to 27oC throughout the year, heat can be extracted from the ground using ground source heat pumps. However harnessing heat at deeper levels from dry rock is not a viable option at this time due to technological and economic restraints. Only about 0.002 PJ of unconventional geothermal heat is being used at present. Projections show that, at most, <20% of conventional and <0.1% of unconventional sources of geothermal heat will be used in the next 10 years due to accessibility and a number of economic, environmental, social, political and technological barriers.

KEYWORDS Geothermal, direct heat use, conventional sources, unconventional sources, ground sources heat pumps, conductive heat flow.

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1.0 SOURCES OF GEOTHERMAL ENERGY FOR DIRECT USE

A geothermal resource is a volume of rock where heat can be economically harnessed for conversion to power or direct utilization. Heat is mined from fluids circulating in the rock or, in the case of geothermal ground source heat pumps, directly from the ground or circulating groundwater. The absolute temperature of a rock or fluid that can be considered geothermally significant could be as low as 4oC (Lund and Freeston, 2001), because of technological advances in heat pumps and their increasing use in Europe, the USA (Fridleifsson, 2003; Rybach and Sanner, 2000) and Japan (Yasukawa and Takasugi, 2003), to >350oC. Permeability and the presence of circulating fluids can range from high to nearly nil (Figure 1). Hence, essentially New Zealand is one big geothermal system with pockets of subsurface exploitable temperatures where heat can be mined economically from circulating fluids and/or dry rock. In this report conventional geothermal sources refer to geothermal systems where large quantities of hot water or steam can be tapped economically from permeable zones at <3500m for direct use or power generation. These systems usually discharge hot springs and fumaroles on the surface. Unconventional geothermal sources include any source of heat from the earth outside hot spring systems (Figure 1) where permeability and fluid flow may be marginal and the heat low-grade. High-grade heat can be extracted economically from circulating fluids using conventional extraction and energy conversion (e.g., heat to electricity) techniques. The harnessing of low-grade heat systems, which have insufficient permeability to induce flow and hardly any circulating fluid and which may be deep-seated, requires unconventional or experimental techniques such as EGS (Engineered or Enhanced geothermal systems, (www.eere.energy.gov) and is usually not economically viable at present.

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Figure 1. Conventional and unconventional sources of geothermal energy in New Zealand for direct use and power generation and their general temperatures, source depths, permeability, heat grade and presence of circulating fluids. ORC= Organic Rankine Cycle, NE= Natural Energy engine.

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The conventional sources of geothermal energy for power generation and direct heat utilisation in New Zealand include (1) high enthalpy geothermal systems in the (TVZ) and Ngawha, used mainly for power generation at present, and (2) hot spring systems outside these two regions that can be used for direct heat and power generation using binary systems. Unconventional sources of geothermal energy include: (1) natural conductive heat flow from the earth at depths where temperatures remain constant, from about 15m and deeper, found at the edges of high-enthalpy geothermal systems in the TVZ and Ngawha, in sedimentary basins and igneous terrain with some water circulation and hot dry rock at >4000m and (2) warm to hot water in abandoned hydrocarbon wells and flooded underground coal and mineral mines (Figure 1).

2.0 PRESENT DIRECT HEAT USE FROM GEOTHERMAL SOURCES

The majority of direct heat uses in New Zealand are exploited from hot spring systems, including the producing geothermal systems in the TVZ and Ngawha. However only <0.1% is being utilised from unconventional sources of geothermal energy such as the 27oC waters from a hydrocarbon well in New Plymouth, Taranaki used for commercial baths and production of mineral waters and the use of geothermal heat pumps in Blenheim and Timaru (White, 2006), for example.

Hot spring systems have a wide use of direct heat uses, most common of which are swimming and bathing followed by space-heating and various domestic uses such as bathing and washing (Figure 2). In terms of energy extracted however (Figure 3), drying (81%) is dominant over swimming and bathing (9%).

A recent study shows that New Zealand has an installed capacity of 448 megawatts thermal (MWt), or 14.14 PJ, for direct heat utilisation of geothermal energy (White, 2006). The amount of energy in PJ, used in one year is derived from MWt using Equation 1:

Energy in 1 year (PJ) = energy (MWt) x 8766 hours/year x 0.0000036 Equation 1

About 62% of the installed capacity is derived in conjunction with the operation of four power- generating geothermal systems in the TVZ using outflow from the power plant or from discharging wells. These include Wairakei (prawn farming, greenhouse for orchid-growing), Ohaaki-Broadlands (timber drying, space heating), Mokai (vegetable growing in greenhouse, bathing, tourism park) and Kawerau (timber and paper drying, space heating). The rest, 38%, are derived from other hot spring systems in the TVZ, other regions of North Island and in the South Island (White, 2006).

In summary, the geothermal energy extracted for direct use, at present, is 14.14 PJ.

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Figure 2. Drect heat uses in various hot spring systems of New Zealand (data from White, 2006).

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Figure 3. Direct heat uses in terms of relative percentage of extracted energy (data from White, 2006).

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3.0 CONVENTIONAL SOURCES OF GEOTHERMAL ENERGY

3.1 HOT SPRINGS

There are 25 major hot spring systems in the TVZ and at least another 100 outside this region (Figure 4), containing at least one spring. About 80% of the hot springs in the North Island are being used, ranging from commercial baths as in Waiwera, domestic use (Maketu), tourism (Rotorua), therapeutic use (Te Puia) and bathing spots (Kawhia). In

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Figure 4. Hot spring system locations and direct heat usage in New Zealand.

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the South Island, however, <10% are used regularly because most are remote, located within at least two hours walk from the nearest road, and are thus only occasionally used by trampers or hunters. In some regions, such as Waiwera, Parakai and Tauranga in the North Island, most of the springs have stopped flowing because of lowered water levels and pressures and all the hot waters presently discharged from wells.

The TVZ has at least 7500 MWt (237 PJ) of energy available from surface springs, including the springs in the Waikato River, Lake Taupo and Lake Rotorua (Bibby et al, 1995). At least another ~160 MWt are present in hot springs outside the TVZ, with 135 MWt (4.26 PJ) in the North Island and 25 MWt (0.8 PJ) in the South Island.

3.2 CASCADE AND PARALLEL USES FROM OPERATING GEOTHERMAL SYSTEMS

3.2.1 Cascade uses

Reinjection is the norm for most power producing geothermal systems in the world and any New Zealand system that may be developed in the future will most likely require reinjection of waste fluids.

Figure 5. Cascade use of waste water for prawn farming in Wairakei. The power plant is on the left and the prawn farm on the right.

At present, Kawerau discharges about 170 kg/s or 50% of its waste hot waters into the Tarawera river (Young and White, 2005) at 95oC (Dunstall, 1999). Wairakei discharges about 257 MWt of its 130oC wastewaters into the Waikato river (estimated from www.nzgeothermal.org.nz).

Thus about 6.7 PJ of energy are wasted in Wairakei and Kawerau (Appendix 1) that can be cascaded into several direct heat uses. For example, the 5.3 PJ of 130oC waste waters available in Wairakei can be harnessed for an agricultural business complex, in cooperation with orchards and farms in the Waikato or Gisborne and Napier. The complex may include, for example, a sequence of processes from high to low temperature e.g., refrigeration (using 120oC waters), drying of grain, vegetables and fruit (100-110oC), alcohol distillation from fruit and tubers (75-85oC) and freeze distillation of alcohol, or use geothermal waste water to produce bioethanol for fuel (e.g., Figure 6).

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Figure 6. Two cascade options for an agri-business complex using 130oC wastewater in Wairakei. Total energy usage for each process is roughly estimated and assumptions are shown above.

3.2.2 Parallel uses

Parallel uses may involve drilling of new wells or using discarded wells for direct heat uses, in a developed power-generating field, e.g., the greenhouse in Mokai and the pulp and paper mill in Kawerau.

In calculating the potential energy for direct heat uses parallel to power generation, the following are assumed:

1. Twenty geothermal systems have been developed for power generation including Wairakei, Mokai, Ohaaki-Broadlands, Mokai, Rotokawa, Kawerau, Rotorua and Ngawha.

2. (In geothermal systems with >1 MWe potential (Lawless, 2002) at least two wells are dedicated for direct heat use.

3. Where direct heat utilisation is already employed such as in Wairakei, Mokai, Ohaaki, Mokai and Kawerau, only one well is assumed (Appendix 1).

4. Minimum discharge temperature from the wells dedicated to direct heat use is 180oC (763 kj/kg) and the flow is at least 5 L/s.

A shown in Table 1 the minimum total energy from parallel use of geothermal energy is 2.53 PJ.

In summary conventional sources of geothermal heat, which include hot spring systems and cascade and parallel uses of geothermal fluids from power-producing systems, have a potential total energy of at least 265 PJ of which only 5% is presently being used.

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Table 1. Conservative projected energy use, in megawatts thermal (MWt) and petajoules (PJ), of parallel direct heat usage in power-producing geothermal systems.

Potential Number of Area generating wells for MWt PJ capacity1 parallel use

Atiamuri 1 1 3.8 0.12 Horohoro 1 1 3.8 0.12 Kawerau 350 1 3.8 0.12 Ketetahi off limits 0.0 0.00 Mangakino 20 2 7.6 0.24 Mokai 95 1 3.8 0.12 Ngatamariki 90 2 7.6 0.24 Ngawha 50 2 7.6 0.24 Ohaaki 100 1 3.8 0.12 Orakeikorako 90 2 7.6 0.24 Reporoa 20 2 7.6 0.24 Rotokawa 230 2 7.6 0.24 Rotorua 25 1 3.8 0.12 Rotoma 28 2 7.6 0.24 Tauhara 200 2 7.6 0.24 Te Kopia 75 2 7.6 0.24 Tikitere 160 2 7.6 0.24 Tokaanu 130 2 7.6 0.24 Waimangu 180 2 7.6 0.24 Waiotapu 250 2 7.6 0.24 Wairakei 380 1 3.8 0.12 TOTAL 3.96 1from Lawless (2002)

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4.0 UNCONVENTIONAL SOURCES OF GEOTHERMAL ENERGY

4.1 INTRODUCTION

The heat in place for unconventional sources of energy in New Zealand is estimated using Equation 2.

Total heat in place = Heat in Rock + Heat in Circulating Fluid i.e.,

Total heat in place =[ V(1-Φ)Crockρrock(Tf -To)] + [VΦCwaterρwater(Tf -To)] Equation 2

Where: V = volume in m3 Φ = porosity

Crock = heat capacity of rock in kJ/kg) 3 ρrock = density of rock in kg/m ) Cwater = heat capacity of water (4.18 kJ/kg) 3 3 ρwater = density of water in kg/m (1000 kg/m ) o To = base temperature (15 C used in report) Tf = source temperature for extraction of geothermal energy

Where the rock is dry and low in permeability and circulating fluids, a porosity of 0.01 is assumed. In flooded underground mines, where heated flood waters fill mine caverns, a porosity of 1.0 is assumed.

Heat capacity and density values for andesite and greywacke, rock formations generally intersected at depth in New Zealand, are shown in Table 2.

The calculations in this report are rough estimates and need to be updated in the future by:

1. Refining the surface heat flow map into smaller regions that may be accessed later on by people who may wish to install ground source heat pumps, for example,

2. Correcting or rechecking certain regions of the present heat flow map of New Zealand,

3. Estimating the heat flow and heat reserves at various depths in New Zealand,

4. Defining the heat capacity, density and porosity of the various lithologies intersected at various depths and temperatures,

5. Refining the base temperatures used in the different regions and,

6. Establishing factors that affect the efficiency of energy extraction from various sources of unconventional geothermal energy and define this parameter for heat reserve calculations.

One of the most basic data used in calculating heat at depth is heat flow. Heat flow trends within a large area of the TVZ is fairly well-defined by the temperature measurements in numerous wells drilled in the geothermal areas and several heat flow studies (e.g. Studt and Thompson, 1969; Alllis, 1979; Bibby et al, 1984; Bromley and Hochstein, 2000). The main heat flow data for the rest of the country, used in this report, is based on Pandey (1981) and the heat flow isoline map published by Allis et al (1998; Figure 7).

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Table 2. Specific heat capacity and bulk density values of andesite, greywacke and water. Greywacke density data is from Malengreau et al (2000), upper value for andesite from Johnson and Olhoeft (1984). The heat capacity of greywacke is that of sandstone (www.edumine.com) and the heat capacity of granite (www.EngineeringToolbox.com) at 27oC and 100 kPa is used as a proxy for andesite. Water constants are from Weast et al (1989).

Material Heat Capacity (kJ/kg) Density (kg/m3)

Andesite 0.79 2800

Greywacke 0.92 2670

Water 4.18 1000

4.2 CONDUCTIVE HEAT FLOW

The calculation of available heat reserves from conductive heat flow is based on a total area of ~184,415 km2, nearly 70% of the New Zealand landmass that excludes national parks, forest parks, reserves, archaeological sites and protected private land under the jurisdiction of the Department of Conservation (Figure 8) and large lakes outside these areas e.g., Lake Taupo.

In the following calculations the country is divided into two general heat flow regions: low heat flow at <70 mW/m2, where the thermal gradient is 21-33oC, and high heat flow (>70mW/m2) where the thermal gradient is >33oC/km. In regions of low heat flow, a thermal gradient of 28oC/km is used in the calculations. Within the high heat flow region a thermal gradient of 33oC/km is used outside the TVZ, Coromandel-Thames and Ngawha-Northland subdivisions.

On land, the TVZ has a total area of 9000 km2 with about 18% (1620 km2) occupied by parts of the Tongariro National Park, and other protected forests, and parks in the region. Lake Taupo has an area of 616 km2 (www.doc.govt.nz). The area encompassed by the geothermal systems is 291 km2 (Figure 9; Appendix 2; Bibby et al, 1995). Therefore the area in the TVZ used in the evaluation of low-grade heat is about 6,475km2. The regional thermal gradient used in calculating heat reserves in this region is 50oC/km (Table 3).

The area of Coromandel is about 2300 km2 with 30% of the land governed by the Department of Conservation (www.doc.govt.nz) leaving an area of 1,610 km2 for possible heat exploitation. The area is within the 80 mW/m2 heat flow isoline and the thermal gradient is about 40oC.

The whole of Northland has an area of 6670 km2 with 1680 km2 under the jurisdiction of the Department of Conservation (www.doc.govt.nz). About 65% of this area is encompassed by the 80 mW/m2 heat flow isoline (Figure 7). The total area used in the calculations is 3245 km2 and the thermal gradient set at 40oC/km, similar to Coromandel-Thames.

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Figure 7. Conductive heat flow map of New Zealand (Allis et al, 1998). Contours in mWm-2).

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Figure 8. Map showing areas under the jurisdiction of the Department of Conservation (blue), regions with thermal gradient >33oC/km (yellow), <33oC/km (outside yellow regions), the TVZ, Coromandel and Northland.

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Figure 9. Geothermal areas in the TVZ (from Bibby et al, 1995).

Table 3. Areas with thermal gradients of 21-33oC and >33oC outside environmentally- and socio-politically- sensitive regions administered by the Department of Conservation, shown in Figure 8. The total area of New Zealand is 264,787 km2. Percentages are with respect to total land area.

Area/ Thermal Gradient 21-33oC/km >33oC/km

South Island 75,000 km (28.3%) 18,800 km (7.1%)

North Island

Ngawha Northland 3,245 (1.2%)

Coromandel 1,610 (0.6%)

Taupo Volcanic Zone 6,475 (2.4%)1

Other regions of North Island 71,422 (27.0%) 7,865 (3.0%)

1area excludes geothermal systems and land administered by the Department of Conservation

Regions in the South Island with thermal gradients of >40oC/km are largely under the administration of the Department of Conservation and are not included in the calculations.

Figure 10 shows the distribution of estimated temperatures at 250m depth in New Zealand.

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Figure 10. Estimated constant temperatures at 250m depth.

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4.2.1 Heat Reserves in Dry Rock at Shallow Depths (<250m)

Estimates of heat reserves and extractable heat for possible geothermal use are shown in Table 4 for shallow depths where heat may be harnessed through closed-loop ground source heat pumps using wells with maximum depths of 250m where temperatures range from about 21o to 28oC (Figure 10).

A recovery factor for mining heat from unfractured ground is arbitrarily set at 1% in this report, resulting to nearly 8,400 PJ of potential extractable heat from the upper 250m of the crust in New Zealand that is accessible for exploitation.

Table 4. Estimate of heat reserves from 250m for ground source heat pump use. In the calculation, porosity is arbitrarily set at 0.01, the thermal gradient used for low thermal gradient regions is 28oC/km, 50oC/km for the TVZ, 40oC/km for Coromandel and Ngawha Northland and 33oC/km for the rest of the North Island and parts of the South Island. C= heat capacity, ρ= density; initial temperature = 15oC; recovery factor = 1%.

Potential Extractable Temperature Volume C ρ Total Heat Energy Thermal gradient Area (km2) (oC) at 250m (m3) (kJ/kg) (kg/m3) Reserves (1% ) PJ PJ

SHALLOW (<250 m) Low thermal gradient (21-33oC/km) North and South Islands 146,420 21.5 3.66E+13 0.92 2,670 633,832 6,338 High thermal gradient (>33oC/km) Taupo Volcanic Zone 6,475 27.5 1.62E+12 0.79 2,800 36,125 361 Coromandel 1,610 25.0 4.03E+11 0.79 2,800 8,982 90 Ngawha Northland 3,245 25.0 8.11E+11 0.92 2,670 20,067 201 other parts of North Island 7,865 23.5 1.97E+12 0.92 2,670 41,300 413 South Island 18,800 23.5 4.70E+12 0.92 2,670 98,800 988 TOTAL 8,392

4.2.2 Heat Reserves in Dry Rock at 120oC

The minimum depth where a temperature of 120oC can be intersected varies from about 2,100m in the Taupo Volcanic Zone to >3,800m in regions of lower conductive heat flux. One percent of the total estimated heat reserves in all regions, at depths where 120oC is projected, is enormous at more than 1,700 EJ. However most of this heat energy cannot be harnessed because the technology to use this heat is not yet well-developed and other sources of energy are more economical.

Wellbore heat exchangers, used for EGS, may be used in the future to mine low-grade heat from deep levels of sedimentary basins and igneous terrain. Essentially, cold water from the surface is injected to depths, that are often artificially fractured (e.g., Asanuma et al, 2005), where temperatures are >200oC. Surface waters introduced through a well are heated at depth by conduction and then extracted via the same well or adjacent wells (Smith, 1983; White, 1983). At present the well bore heat exchanger concept is still experimental (Nalla et al, 2004), with most of the studies carried out in Soultz, France and Cooper basin, Australia (e.g., Baria et al, 1999; Swenson et al, 2000).

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Table 5. Estimate of heat reserves from depths where temperatures are about 120oC. In the calculation, porosity is 0.01, the thermal gradients used for the different regions are the same as in Table 4.

1% of Total Total Heat Heat Depth Volume C ρ Reserves Reserves Thermal gradient Area (km2) (m) at 120oC (m3) (kJ/kg) (kg/m3) PJ PJ

DEEP (temperature <120oC) Low thermal gradient (21-33oC/km) North and South Islands 146,420 3,800 5.56E+14 0.92 2,670 144,513,723 1,445,137 High thermal gradient (>33oC/km) Taupo Volcanic Zone 6,475 2,100 1.36E+13 0.79 2,800 3,186,253 31,862 Coromandel 1,610 2,600 4.19E+12 0.79 2,800 980,890 9,809 Ngawha Northland 3,245 2,600 8.44E+12 0.92 2,670 2,191,357 21,914 other parts of North Island 7,865 3,200 2.52E+13 0.92 2,670 6,540,000 65,400 South Island 18,800 3,200 6.02E+13 0.92 2,670 15,600,000 156,000 TOTAL 1,730,346

Large amounts of low grade heat may be present at depth but are virtually unusable at present except in regions where deep wells or deep mines have encountered heated water.

4.2.3 Heated Water in Abandoned Hydrocarbon Wells

There are 349 onshore abandoned hydrocarbon wells in New Zealand (Figure 11; Appendix 3) drilled to depths of 17 to 5065m with bottom hole temperatures from 16oC to 170oC. Forty percent of these wells (140) are found in Taranaki, within or near populated areas, where cogeneration of energy using geothermal and gas is possible. Wells deeper than 4000m occur mostly in Taranaki, except for one in the East Coast. Seventy-five percent (265) of the onshore wells have bottom hole temperatures <75oC, and 15% (55) have temperatures between 100-120oC. Except for 3 wells, all wells with bottom hole temperatures >120oC are found in Taranaki. The 3 wells outside Taranaki are found in Northland (125oC), the East Coast of North Island (150oC) and the West Coast of South Island (130oC; Reyes, 2007).

Water and/or gas is present in most of the abandoned wells ranging from brines to low-Cl groundwaters. Assuming a water flow of 4 L/s either from artesian pressures (King and Thrasher, 1996) or by use of a down hole pump, the total thermal energy from these wells amounts to at least 317 MWt (10.0 PJ). The wells can be used for various direct heat uses ranging from ground source heat pumps to milk pasteurization, drying, plant cultivation in greenhouses, alcohol distillation, bioethanol production, etc (Figure 12).

The highest number of abandoned wells, with bottomhole temperatures of ~80oC, which flow because of artesian pressures, occur in Taranaki where use of geothermal heat may benefit the large horticultural and dairy industries of the region. The minimum extractable heat in the abandoned onshore wells in Taranaki is 178 MWt (5.6 PJ), assuming a flow of 4 L/s.

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Figure 11. Location of onshore abandoned oil and gas wells.

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4.2.4 Heated Water in Abandoned Underground Mines

There are about 22 abandoned underground coal mines (Isaac, 1985; Fowke, 1987; Barry et al, 1994; Edbrooke et al, 1994), at least nine underground gold mines and one copper mine (Wodzicki and Weissberg, 1970; Christie and Brathwaite, 1997; Cox, 2000; R Brathwaite, pers. comm, 2007) which are flooded (Figure 13). Low-grade heat from the heated flood waters may be harnessed by ground source heat pumps.

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Figure 13. Location of flooded abandoned underground coal and mineral mines, used in calculating the available low-grade heat from flood waters in mine caverns. Heat flow (red) in mWm-2.

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Table 6. Extractable heat energy from warm waters in abandoned underground mines.

Underground Volume (m3) Tf (oC) C (kJ/kg) ρ (kg/m3) PJ Mines

Coal Mines Northland Kawakawa 9000000 20.0 4.18 1000 0.015 Hikurangi 98350000 20.0 4.18 1000 0.069 Kamo 54500000 20.0 4.18 1000 0.027 Kiripaka 31570000 20.0 4.18 1000 0.010 Avoca 76500 20.0 4.18 1000 0.0002 Waikato Drury 10862 17.5 4.18 1000 0.0001 Maramarua 10930075 17.5 4.18 1000 0.0019 Whatawhata 519348 17.5 4.18 1000 0.0025 Te Kuiti 1283096 17.5 4.18 1000 0.0003 Huntly East 33890020 17.5 4.18 1000 0.0345 Rotowaro 244399185 17.5 4.18 1000 0.2488 Glen Massey 26069246 17.5 4.18 1000 0.0265 Kawhia 814664 17.5 4.18 1000 0.0008 Taranaki Aria 179905 20.0 4.18 1000 0.0009 Ohura 56211813 20.0 4.18 1000 0.0229 West Coast Greymouth 7976918 23.8 4.18 1000 0.014 Denniston 5655125 17.5 4.18 1000 0.010 Charleston 142566 17.5 4.18 1000 0.0003 Otago Green Island 171079430 17.5 4.18 1000 0.035 Kaitangata 590631365 17.5 4.18 1000 0.120

Gold Mines Hauraki 27.0 4.18 1000 Martha's mine 275000000 25.0 4.18 1000 11.495 Golden Cross 720000 22.5 4.18 1000 0.023 Karangahake 1 1820000 32.5 4.18 1000 0.133 Karangahake 2 330000 22.5 4.18 1000 0.010 Tui (copper mine) 5761350 18.8 4.18 1000 0.090 Otago Imperial reform 8640000 19.5 4.18 1000 0.163 Just in time 2268750 23.3 4.18 1000 0.078 Fiery Cross 7252000 22.0 4.18 1000 0.212 Welcome hopeful 31654000 24.5 4.18 1000 1.257 Specimen 2268750 19.1 4.18 1000 0.039 Birthday reef 856000 35.0 4.18 1000 0.072

Copper Mine Hauraki 27.0 4.18 1000 Tui (copper mine) 5761350 18.8 4.18 1000 0.090 TOTAL 14.21 Notes: porosity = 1; To = 15oc; Tf= temperature at bottom of mine calculated from thermal gradient of region; c= heat capacity of water; ρ = density of water

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Estimated temperatures in the coal mines range from 18o to 24oC, with a mean of 18oC. Temperatures are higher in gold mines at 19o to 35oC with a mean of 23oC mainly because the mines could be as deep as 700 to 850m and are also located in high heat flux areas in the Coromandel and the South Island where the thermal gradient is about 35-40oC/km (Table 6).

The volume of the underground coal mines are calculated from the total mass extracted divided by the mean density of coal at about 1260 kg/m3. For the gold and copper mines the area covered by the underground mines and the depth of the deepest stopes are included in the calculation. The estimated potential heat energy from the warm waters is about 0.64 PJ for the 22 coal mines and 13.6 PJ for the gold and copper mines.

5.0 PROJECTED USE OF UNCONVENTIONAL GEOTHERMAL RESOURCES

5.1 SHALLOW CONDUCTIVE HEAT FLOW AND GROUND SOURCE HEAT PUMPS

In calculating the attainable use of heat for ground source heat pumps in New Zealand for the next 10 years, it is assumed that about 5% of the buildings in New Zealand will have at least 6 kW installed.

According to New Zealand Statistics, there are 1,961,290 buildings in New Zealand of which 309,750 are business buildings and 1,651,540 dwellings. About 18.6 PJ will be harnessed if 5% of the buildings (98,065) will have a 6 kW ground source heat pump installed within the next 10 years (Table 7).

5.2 ABANDONED HYDROCARBON WELLS

In the next 10 years about 20 of the 140 abandoned wells in Taranaki could be exploited for geothermal direct heat uses, approximately amounting to 25 MWt or 0.5 PJ on an annual basis. Another 20 could probably be harnessed for use with 6 kW ground source heat pumps amounting to an additional 0.004 PJ. Hence for the next 10 years, at least 0.504 PJ may be exploited from these wells.

5.3 ABANDONED UNDERGROUND MINES

Within the next 10 years two mines could probably be installed with 6 kW ground source heat pumps yielding an energy of 0.0004 PJ. Access to abandoned underground mines may, however, be hampered by several factors such as high concentrations of combustible gas in some coal mines, cave-ins, highly polluted environment as in the Tui mine and distance from populated areas. In some cases the abandoned mines may be filled-in and secured.

6.0 SUMMARY AND CONCLUSIONS

Potential sources of geothermal energy in New Zealand are widespread and are not only confined to active volcanic regions such as the TVZ and Ngawha in Northland (Figure 14). The sources of geothermal energy include (1) more than 100 hot spring systems occurring all over New Zealand, ranging in temperatures from 17oC to 100oC, (2) heated waters in abandoned hydrocarbon wells and flooded underground coal and mineral mines and (3) conductive heat in rock below 15m that can be harnessed by ground source heat pumps and in the future, by using the wellbore heat exchangers.

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Table 7. Present and potential extractable energy from geothermal systems in New Zealand for direct heat use. See calculations in appendices. GSHP= ground source heat pump.

GEOTHERMAL RESOURCE EXTRACTABLE ENERGY (PJ) DIRECT HEAT USE Present use Added Potential Can be Estimated use Harnessed in 10 years Conventional 1. Waste water and steam from power 8.81 cascade: 6.85 yes cascade: 4.1 generating geothermal systems in the parallel: 3.96 yes parallel: 0.3 TVZ (cascade and parallel uses) 2. Hot spring systems outside the TVZ 3.22 3.5 yes 2.0 (including producing wells) 3. Hot spring systems in the TVZ 2.23 237 yes 30 (including wells in Rotorua and Tauranga) SUBTOTAL 14.2 251.31 36.4 Unconventional 4.1 Heat at shallow depths -Dry rock (conductive heat) at <250m 8,392 some 18.6 -Heated water from abandoned wells (0.82) some 0.004 -Heated water from abandoned mines (0.9) some 0.0004 4.2. Deep heat - Dry rock (conductive heat) at >2100 1,730,346 not yet - - Heated water from abandoned wells at 0.0024 (9.20) some 0.500 >250m

-Heated water from abandoned mines (13.3) some - SUBTOTAL 0.00024 1,738,738 19.1 TOTAL 14.2 1,738,989 55.5 Notes: 1 calculated from White (2006); 2 White (2006) and A G Reyes field notes; 3 White (2006), 4use of Bonithon – 1 in Taranaki in a spa

The hot spring systems, including use of hot water from power-producing geothermal systems, or conventional sources of geothermal energy, has an extractable energy of about 267 PJ of which only 5%, at 14.2 PJ, is presently being used (Table 7).

There is an enormous amount of heat available below 15m (Table 7). However, >99% of this enormous heat reserve (Figure 15) are inaccessible because the technology to extract heat from deep-seated rock with little permeability and very limited circulating fluids is not yet well- developed (e.g., Nalla et al, 2004). Less than 0.01% of this heat may be harnessed through the use of ground source heat pumps from wells drilled to relatively shallow depths (<250m), or by using heated waters found in abandoned hydrocarbon wells and underground mines (Table 7).

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reyes 07

Figure 14. Map of New Zealand showing the conductive heat flow contours (Allis et al, 1998), hot spring systems and their discharge temperatures in the TVZ, Ngawha and areas outside these two, abandoned hydrocarbon wells and the location of some underground coal and gold or copper mines.

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reyes 07

Figure 15. Potential energy from conventional and unconventional sources of heat in New Zealand. *Does not include the edges of geothermal systems in the TVZ.

This preliminary study shows that subsurface heat reserves for geothermal direct heat use are widespread and enormous. However, most of the unconventional sources of geothermal energy are inaccessible using present technology. There are also other factors that may limit the widespread direct heat use of geothermal energy within the next 10 years. These include:

1. Low demand caused by the small population of the country and equable climate for 76% of the population who live in North Island. The latter may limit the number of ground source heat pump (GSHP) use in the North Island but fierce winters in some parts of South Island may create a niche market for use of GSHP.

2. Abundance of other energy sources e.g., solar, wind, land-fill gas.

3. General lack of knowledge regarding the widespread presence of geothermal resources outside the TVZ and the various ways to use direct heat from the ground by the public.

4. Limited legislation and support from the government that encourage use of low carbon emission renewable sources of energy like geothermal.

5. Limited government support for research on direct heat sources and utilisation. Foundation for Research Science and Technology (FRST) is cutting back completely any funds for research on this area by next financial year.

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6. A general lack of communication between sectors (e.g. agricultural; fuel production; building contractors) that may benefit from geothermal energy and the producers/owners of geothermal systems.

7. Hindrances from private interests e.g., private ownership either by individual families, tribes or companies of land that may contain exploitable geothermal systems such as hot springs and hydrocarbon wells.

8. Technological advances to exploit low grade heat from depth in low-permeability dry rock are not yet economically feasible at present.

9. Environmental considerations (although areas under the jurisdiction of the Department of Conservation land are excluded from heat calculations).

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7.0 REFERENCES

Allis R G (1979) Heat flow and temperature investigations in thermal ground. DSIR Geophysics Division Report 135, 28 p. Allis R G, Funnell R and Zhan X (1998) From basins to mountains and back again: NZ basin evolution since 10 Ma. Proceedings 9th International Symposium on Water-rock Interaction, Taupo New Zealand, 3-7. Anasuma H, Soma N, Kaieda H, Kumano Y, Izumi T, Tezuka K, Niitsuma H and Wyborn D (2005) Microseismic monitoring of hydraulic stimulation at the Australian HDR project in Cooper Basin. Proceedings World Geothermal Congress 2005, Turkey. Baria R, Baumgartner J, Gerard A, Jung R and Garnish J (1999) European HDR research programme at Soults-sous-Forets (France) 1987-1996. Geothermics, 28, 655-670. Bromley C J and Hochstein M P (2000) Heat transfer of the Karapiti fumarole field (1946- 2000). Proceedings of the New Zealand Geothermal Workshop, 87-92. Barry J M, Duff S W and Macfarlan D A B (1994) Coal Resources of New Zealand. Coal report series CR3132. Ministry of Economic Development. Bibby H, Caldwell G, Davey F and Webb T (1995) Geophysical evidence on the structure of the Taupo Volcanic Zone and its hydrothermal circulation. Journal of Volcanology and Geothermal Research, 68, 29-58. Christie A and Brathwaite R (1997) Gold. Mineral commodity report 14 - gold. New Zealand Mining, 21, 21-40. Cox S C (2000) The geometry of mineralisation and exploration models for the Blackwater mine in the Reefton Goldfield. 2000 New Zealand Minerals and Mining Conference Proceedings, 125-136. Dunstall M (1999) Small power plants: recent developments in geothermal power generation in New Zealand. GHC Bulletin December 1999, 5-12. Edbrooke S W, Sykes R and Pocknall D T (1994) Geology of the Waikato coal measures, Waikato coal region, New Zealand. Institute of Geological and Nuclear Sciences Monograph 6. Fowke N C (1987) Waikare coalfield assessment of exploration 1975-1982. New Zealand Geological Survey Report M157. Fridleifsson I B (2003) Status of geothermal energy amongst the world’s energy sources, Geothermics, 32, 379-388. Isaac M (1985) Coalfield geology and coal prospects in Northland. New Zealand Coal Resources Survey Record 4. Johnson G and Olhoeft G (1984) In: Carmichael R S (ed), Handbook of physical properties of rocks. 3, CRC Press, Boca Raton, Florida, USA. King P R and Thrasher, G P (1996) Cretaceous-Cenozoic geology and petroleum systems of the Taranaki Basin, New Zealand. Institute of Geological and Nuclear Sciences Monograph 13. Lawless J V (2002) New Zealand’s geothermal resource revisited, NZGA Seminar. Lund J W and Freeston D H (2001) World-wide direct uses of geothermal energy 2000, Geothermics, 30, 29-68. Malengreau B, Skinner D, Bromley C and Black P (2000) geophysical characterisation of large silicic volcanic structures in the Coromandel Peninsula, New Zealand. New Zealand Journal of Geology and Geophysics, 43, 171-186. Nalla G, Shook G M, Mines G L and Bloomfield K K (2004) parametric sensitivity study of operating and design variables in wellbore heat exchangers. Idaho National Engineering and Environmental Laboratory report INEEL/EXT-03-01433, 56 p. Pandey O P (1981) Terrestrial heat flow in the North Island of New Zealand. Journal of Volcanology and Geothermal Research, 10, 309-316.

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Reyes A G (2007) Abandoned oil and gas wells – a reconnaissance study of an unconventional geothermal resource. GNS Science report 2007/23. Rybach, L and Sanner B (2000) Ground source heat pump systems, the European experience, GHC Bull (2000), 16-26. Smith M (1983) A history of hot dry rock geothermal energy systems. Journal of Volcanology and Geothermal Research, 15, 1-20. Studt F E and Thompson G E K (1969) geothermal heat flow in the North island of New Zealand, New Zealand Journal of Geology and Geophysics, 12, 673-683. Swenson D P, Chopra and Wyborn D (2000) Initial calculations of performances for an Australian hot dry rock reservoir. Proceedings World Geothermal Congress 2000, Japan, 3907-3912. Thain I, Reyes A G and Hunt T (2006) A practical guide to exploiting low temperature geothermal resources. GNS Science Report 2006/09. Weast RC, Lide DR, Astle M J and Beyer W H (1989) CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data. 70th edition, CRC press, Boca Raton, Florida, USA. White A A L (1983) Sedimentary formations as sources of geothermal heat. Journal of Volcanology and Geothermal Research, 15, 269-284. White B (2006) An assessment of geothermal direct heat use in New Zealand. New Zealand Geothermal Association Inc, 30 p. Wodzicki A and Weissberg B G (1970) Structural control of base metal mineralisation at the Tui mine, Te Aroha, New Zealand. New Zealand Journal of Geology and Geophysics, 13, 610- 630. Yasukawa, K and Takasugi, S (2003) Present status of underground thermal utilization in Japan. Geothermics, 2, 609-618. Young, R (2005) Consent Scenarios for the Kawerau Geothermal Field, Industrial Research Limited.

Others: • www.doc.govt.nz • www.edumine.com • www.EngineeringToolbox.com • www.eere.energy.gov • www.nrc.govt.nz • www.nzgeothermal.org.nz • www.stats.govt.nz

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APPENDIX 1. WASTE WATER AND STEAM FROM POWER GENERATING GEOTHERMAL SYSTEMS IN THE TVZ (CASCADE AND PARALLEL USES)

1.1 CASCADE USES

1.1.1 Wairakei

Total water discharged from power plants: 1472kg/s Temperature of waters: 130oC (546 kJ/kg) 50% of waste water is reinjected.

Present use of waster water that is not reinjected: 14.4 MWe (3.0 PJ) – Wairakei Binary Cycle power plant (uses about 264 kg/s 130oC waste water and discharges 80oC wastewaters which are reinjected or used by the prawn farm)

89 MWt (1.85 PJ) for the prawn farm

About 472 kg/s of 130oC waters are discharged into the river

Total MWt = 472 kg/s x 546 kJ/kg x .001 = 257 MWt Energy = 5.3 PJ

The unused energy can be used for a multiple purpose agri business complex in cooperation with farms and orchards in the Waikato or Napier and Gisborne for freezing or refrigeration of fruits and vegetables prior to processing (120oC waters), drying of fruit and vegetables (100- 110oC), alcohol distillation from fruits and tubers to (75-85oC) and freeze distillation of alcohol, or a facility for the production of bioethanol for fuel use.

1.1.2 Kawerau

Total water discharged from plants: 340 kg/s 50% is discharged to the river: 170 kg/s Temperature of waters being discharged in river: 95oC (398 kJ/kg)

Total MWt = 170 kg/s x 398 x .001 = 67.7 MWt Energy = 1.4 PJ

Most of this waste energy can be used for greenhouses, drying facilities, alcohol distillation.

1.2 Parallel uses

At least one to two wells per power-producing area (or an existing one used) are drilled to depths where at least 180oC will be intersected, H= 763 kJ/kg, mass flow = 5 kg/s.

Attainable in the next 10 years: Use wells or drill wells for direct heat use in Rotokawa and Ngawha:

Thermal power = 5 kg/s x 763 kJ/kg x 4 wells x 0.001

= 15.2 MWt Energy = 0.32 PJ

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Probable in another 10 years: Drill wells or use existing wells specifically for direct heat use in five other geothermal systems that will be developed:

Thermal power = 5 kg/s x 763 kJ/kg x 10 wells x 0.001

= 38.2 MWt Energy = 0.79 PJ

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APPENDIX 2. WARM GROUNDS AND WATERS AT EDGES OF HIGH- TEMPERATURE GEOTHERMAL SYSTEMS IN THE TVZ

Total areas of geothermal systems in the TVZ (Bibby et al, 1995). Ngawha area from www.nrc.govt.nz.

Areas of Area (m2) fields

Kawerau 18,000,000 Taheke 2,000,000 Waiotapu 18,000000 Reporoa 12,000,000 Te Kopia 11,000,000 Broadlands 12,000,000 Rotokawa 18,000,000 Tauhara 25,000,000 Wairakei 25,000,000 Ngatamariki 7,000,000 Orakeikorako 9,000,000 Mokai 14,000,000 Atiamuri 8,000,000 Tokaanu 20,000,000 Rotoma 20,000,000 Waimangu 20,000,000 Taheke 2,000,000 Tikitere 15,000,000 Mangakino 8,000,000 Horohoro 4,000,000 Rotorua 23,000,000 Ngawha 25,000,000

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APPENDIX 3. ABANDONED HYDROCARBON WELLS

There are 349 extant abandoned hydrocarbon wells in eight onshore sedimentary basins and several non-basin areas. Estimated bottomhole temperatures (this study) range from 15.6 to 171oC assuming a surface temperature of 15oC. The total energy from the wells is 317.5 MWt or 10.0 PJ annually, calculated using a flow of 4 L/s. No capacity factor was used to obtain MWt.

Total Depth BHT Well Name o MWt PJ (m) (C ) Petroleum Creek-5 17.3 15.6 0.27 0.01 No2 Maoriland 19.0 15.7 0.27 0.01 B1 22.0 15.8 0.27 0.01 B4 24.0 15.9 0.27 0.01 Shaft 25.0 15.9 0.27 0.01 Waipai-1 45.0 16.0 0.27 0.01 No1 Lake Brunner 32.0 16.1 0.27 0.01 No4 Lake Brunner 32.0 16.1 0.27 0.01 B2 34.0 16.2 0.27 0.01 Toi Flat-1 55.0 16.2 0.27 0.01 No3 Maoriland 40.0 16.4 0.27 0.01 No4 Maoriland 40.0 16.4 0.27 0.01 No7 Lake Brunner 38.0 16.4 0.27 0.01 Westcott-1 67.0 16.4 0.27 0.01 No5 Maoriland 41.0 16.5 0.27 0.01 No1 Maoriland 44.0 16.6 0.27 0.01 Cutters Bridge-1 48.0 16.8 0.28 0.01 No1 Kotuku Consolidated 51.0 16.8 0.28 0.01 Okoke Bore 61.0 16.8 0.28 0.01 Alton 61.0 16.9 0.28 0.01 Totangi-1A 64.0 17.0 0.28 0.01 Waitangi Hill-1 64.0 17.0 0.28 0.01 Kioreroa-3 54.0 17.1 0.28 0.01 Petroleum Creek-2 59.0 17.1 0.28 0.01 Petroleum Creek-1 64.0 17.3 0.28 0.01 Rangitaike-1 61.0 17.3 0.28 0.01 Pukerau-1 73.0 17.4 0.28 0.01 Waewaepa-1 124.0 17.7 0.30 0.01 Corehole-8 100.0 17.9 0.30 0.01 Waiotapu-1 61.0 17.9 0.30 0.01 Kaiaua-1 108.0 18.1 0.30 0.01 Samuel Syndicate-6 92.0 18.1 0.30 0.01 Taranaki Petroleum-1 94.0 18.1 0.30 0.01 Totangi-1 103.0 18.1 0.30 0.01 Taranaki Petroleum-2 97.0 18.2 0.30 0.01 Bore 251 123.0 18.5 0.30 0.01 Moa Bore 140.0 18.5 0.30 0.01 No6 Lake Brunner 98.0 18.5 0.30 0.01

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Total Depth BHT Well Name o MWt PJ (m) (C ) Waikaia-2 121.0 18.5 0.32 0.01 Carrington Road-2 112.0 18.7 0.32 0.01 Great Barrier-2 92.0 18.9 0.32 0.01 Pukerau-2 118.0 18.9 0.32 0.01 Horotiu Bore-1 137.0 19.2 0.32 0.01 Horotiu Bore-2 137.0 19.2 0.32 0.01 No3 Bore 147.0 19.2 0.32 0.01 A1 122.0 19.4 0.32 0.01 Kioreroa-2 109.0 19.4 0.32 0.01 Ardmore-1 137.0 19.6 0.32 0.01 Te Karaka-1 152.0 19.7 0.34 0.01 Totangi-2 154.0 19.7 0.34 0.01 No5 Lake Brunner 133.0 19.8 0.34 0.01 Totangi-2A 156.0 19.8 0.34 0.01 No8 Lake Brunner 137.0 19.9 0.34 0.01 Rotokautuku-4 114.0 19.9 0.34 0.01 Omata Bore-1 152.0 20.1 0.34 0.01 Victoria 157.0 20.2 0.34 0.01 Limestone Test Bore 148.0 20.3 0.34 0.01 No3 Lake Brunner 147.0 20.3 0.34 0.01 Waiotapu-2 113.0 20.4 0.34 0.01 Whanga Road Bore 195.0 20.4 0.34 0.01 Kauana-1 179.0 20.5 0.35 0.01 Pukerau-3 165.0 20.5 0.35 0.01 Waikaia-1 197.0 20.6 0.35 0.01 Horotiu Bore-3 195.0 20.9 0.35 0.01 Koranga-1 273.0 20.9 0.35 0.01 Horotiu-2 198.0 21.0 0.35 0.01 Horotiu-5 198.0 21.0 0.35 0.01 Kioreroa-1 148.0 21.0 0.35 0.01 Rotokautuku-1 (So.Cross) 145.0 21.2 0.35 0.01 RSE-2 179.3 21.3 0.35 0.01 No3 Kotuku Oilfields 183.0 21.5 0.37 0.01 No2 Kotuku Petroleum 187.0 21.7 0.37 0.01 Santoft-1 312.0 21.7 0.37 0.01 Merryvale-1 239.0 21.8 0.37 0.01 Beta 208.0 21.9 0.37 0.01 Horotiu Bore-4 229.0 22.0 0.37 0.01 Rangitaike-2 194.0 22.4 0.37 0.01 Rotokautuku-2 172.0 22.4 0.37 0.01 Tikorangi-1 221.0 22.4 0.37 0.01 Papatotara-1 261.0 22.5 0.37 0.01 Corehole-9 215.2 22.7 0.39 0.01 Prospect Valley-1 272.0 22.9 0.37 0.01 Ruby Bay-1 281.0 23.0 0.38 0.01 No2 Lake Brunner 229.0 23.2 0.38 0.01

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Total Depth BHT Well Name o MWt PJ (m) (C ) Dargaville-1 248.0 23.3 0.39 0.01 Minerva Borehole 283.0 23.8 0.40 0.01 No2 Kotuku Oilfields 247.0 23.8 0.40 0.01 Tuatapere-1 306.0 23.9 0.40 0.01 Back Ormond Road-1 301.1 24.0 0.40 0.01 Back Ormond Road-2 300.1 24.0 0.40 0.01 Whitianga-1 295.0 24.1 0.40 0.01 RSE-1 263.1 24.3 0.40 0.01 Samuel Syndicate-1 283.0 24.4 0.40 0.01 No9 Lake Brunner 265.0 24.5 0.42 0.01 Great Barrier-1 226.0 24.7 0.42 0.01 Waikato-3 320.1 24.8 0.42 0.01 No1 Kotuku Oilfields 290.0 25.4 0.42 0.01 Westgas-3 310.6 25.4 0.42 0.01 No1 Kotuku Petroleum 293.0 25.5 0.42 0.01 Paddy Gully-1 294.0 25.5 0.44 0.01 Uruti-1 356.0 25.5 0.44 0.01 Samuel Syndicate-9 322.0 25.7 0.44 0.01 Omata Bore-2 323.0 25.8 0.44 0.01 Samuel Syndicate-2 335.0 26.2 0.44 0.01 Westgas-1 346.6 26.6 0.45 0.01 Corehole-11 423.0 27.1 0.45 0.01 Waingaromia Bore 403.0 27.1 0.45 0.01 Prospect Valley-2 430.0 27.5 0.45 0.01 Waihihere-1 421.0 27.6 0.47 0.01 Bore 252 459.0 28.1 0.47 0.01 No3 Kotuku Petroleum 375.0 28.4 0.47 0.01 Kaitieke-1 394.0 28.7 0.49 0.02 Waitangi-1 (Gisborne Oil) 450.0 28.9 0.49 0.02 Vogeltown Bore 422.0 29.1 0.49 0.02 Centre Bush-1 498.0 29.2 0.49 0.02 Chertsey Bore 661.0 29.2 0.49 0.02 Kaimata Bore 407.0 29.3 0.49 0.02 Puketaha-1 475.0 29.5 0.50 0.02 Rakaiatai-1 685.7 29.7 0.50 0.02 Dargaville-2 445.0 29.8 0.50 0.02 Waingaromia-2 502.1 30.1 0.50 0.02 Samuel Syndicate-7 457.0 30.2 0.50 0.02 Kiore-1 536.6 30.3 0.50 0.02 Samuel Syndicate-3 468.0 30.6 0.52 0.02 Waitangi-1 512.7 30.6 0.52 0.02 Corehole-10 445.0 30.7 0.52 0.02 Waitangi-1 513.0 30.9 0.52 0.02 Koporongo-1 590.9 31.6 0.54 0.02 Te Hoe-1 627.0 32.3 0.54 0.02 Taranaki Petroleum-4 511.0 33.0 0.55 0.02

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Total Depth BHT Well Name o MWt PJ (m) (C ) Access Road 476.0 33.1 0.55 0.02 Rangitaike-1A 479.0 33.2 0.55 0.02 Waikato-4 598.5 33.2 0.55 0.02 Rotokautuku-5 560.0 33.7 0.57 0.02 Speedy-1 876.0 33.8 0.57 0.02 Speedy-1 876.0 33.8 0.57 0.02 Peep-O-Day 917.0 34.7 0.59 0.02 Tane-1 (Mangaone) 917.0 34.7 0.59 0.02 Waitangi-2 662.0 35.2 0.59 0.02 Dobson-2 611.0 35.4 0.59 0.02 Karaka-1 614.0 35.5 0.60 0.02 Waipatiki-2 966.0 35.7 0.60 0.02 Kaiaka-1 625.0 35.8 0.60 0.02 Samuel Syndicate-8 625.0 35.8 0.60 0.02 Samuel Syndicate-5 626.0 35.9 0.60 0.02 Ohura-1 635.0 36.2 0.60 0.02 Norfolk Road Bore 762.0 36.8 0.62 0.02 Young-1 1035.0 37.2 0.62 0.02 Blenheim-2 640.0 37.6 0.64 0.02 Dobson-1 682.0 37.7 0.64 0.02 Takapau-1 1059.0 37.7 0.64 0.02 New Plymouth-1 655.0 38.1 0.64 0.02 Moturoa-3 658.0 38.2 0.64 0.02 Waipatiki-1 1097.0 38.5 0.65 0.02 Northland-1 625.9 38.8 0.65 0.02 River Road-1 789.0 39.0 0.65 0.02 Patea East-1 1082.5 39.2 0.65 0.02 Taipo Creek-1 679.0 39.3 0.65 0.02 Leeston-1 1158.5 39.8 0.67 0.02 Mawhera-1 697.0 39.9 0.67 0.02 Arnold River-1 710.0 40.0 0.67 0.02 Mangatawa-1 669.0 40.5 0.69 0.02 Gisborne-1 927.0 40.6 0.69 0.02 Kaimiro-12 835.0 40.8 0.69 0.02 Waiapu-1 774.0 40.8 0.69 0.02 SFL-2 908.0 40.9 0.69 0.02 Glenn Creek-1 739.0 41.0 0.69 0.02 Mangamahoe-1 802.0 41.7 0.69 0.02 Bonithon-2 764.0 41.9 0.70 0.02 Kawhaka-1 852.0 43.4 0.72 0.02 Oamaru-2 665.0 43.5 0.74 0.02 Tautane-1 1328.9 43.5 0.74 0.02 Tatu-1 860.0 43.7 0.74 0.02 Waiapu-2 994.0 44.8 0.75 0.02 Bell Block-2 853.0 45.1 0.75 0.02 Rotary Bore 853.0 45.1 0.75 0.02

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Total Depth BHT Well Name o MWt PJ (m) (C ) Oamaru-1 908.0 45.3 0.75 0.02 Whakamaro-1 916.0 45.5 0.77 0.02 Spotswood-1 925.0 45.8 0.77 0.02 Waikato-5 1013.1 45.9 0.77 0.02 Manutahi-1 1391.0 46.1 0.77 0.02 Whakatu-1 1455.0 46.2 0.77 0.02 Waikato-2 1026.2 46.3 0.79 0.02 J.T. Benny-1 1013.0 46.4 0.77 0.02 Waikato-1 1036.0 46.6 0.79 0.02 Gisborne-2 1192.0 46.8 0.79 0.02 Omata-1 960.0 47.0 0.79 0.02 Bonithon-1 916.0 47.3 0.79 0.02 Tupapakurua-1 1150.0 47.3 0.79 0.02 Maketawa-1 1135.4 47.4 0.79 0.02 Waikaka-1 978.7 47.6 0.80 0.03 T.E. Weily-1 1057.3 47.7 0.80 0.03 Ealing-1 1696.0 48.1 0.80 0.03 Niagara-2 952.0 48.5 0.82 0.03 Ongaonga-1 1573.0 48.7 0.82 0.03 Tapawera-1 1180.0 48.7 0.82 0.03 Waitaria-1B 1150.0 49.0 0.82 0.03 Carrington Road-1 1042.0 49.7 0.84 0.03 Ararimu-1 1057.6 50.3 0.84 0.03 Ahaura-2 1069.0 50.6 0.86 0.03 Patea-1 1613.0 51.1 0.86 0.03 Hohonu-1 1039.0 51.6 0.85 0.03 Kowai-1 1410.0 51.9 0.87 0.03 Card Creek-1 1342.0 53.3 0.89 0.03 Arcadia-1 1479.0 53.7 0.90 0.03 Bell Block-1 1131.0 54.9 0.92 0.03 Aratika-2 1149.0 55.5 0.94 0.03 Mangaone-1 1550.0 56.3 0.94 0.03 Huiroa Bore 1500.0 56.4 0.94 0.03 Kereru-1 1939.0 56.6 0.94 0.03 Ohaupo-1 1207.0 57.0 0.96 0.03 Taradale-1 1660.7 57.7 0.97 0.03 Mason Ridge-1 1880.0 58.0 0.97 0.03 Wingrove-1 1600.0 59.2 0.99 0.03 Moturoa Bore 1329.0 59.3 0.99 0.03 Stantiall-1 2096.0 59.9 1.00 0.03 Kauhauroa-5 1751.0 60.0 1.00 0.03 Tarata-1 1527.0 60.8 1.02 0.03 Uruti-2 1553.0 60.9 1.02 0.03 Oru-1 1700.0 61.1 1.02 0.03 Happy Valley-1A 1600.0 61.5 1.04 0.03 Happy Valley-1 1623.0 62.1 1.04 0.03

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Total Depth BHT Well Name o MWt PJ (m) (C ) Ratapiko-1 1597.0 62.1 1.06 0.03 Murchison-1 1245.0 62.4 1.04 0.03 SFL-1 1663.0 62.5 1.06 0.03 Windsor-3 1555.6 63.1 1.06 0.03 Kumara-2A 1697.0 63.5 1.07 0.03 Waimamaku-1 1273.0 63.5 1.06 0.03 Windsor-2 1469.4 64.0 1.07 0.03 Kumara-2 1756.0 65.2 1.09 0.03 Rotokautuku-1 625.1 65.6 1.10 0.03 Standish-1 1845.0 66.0 1.10 0.03 Te Rapa-1 1684.0 66.3 1.10 0.03 Totangi-1B 1737.0 68.8 1.16 0.04 Morere-1 2037.0 69.3 1.16 0.04 Toetoe-6A 1817.0 69.5 1.17 0.04 Kokatahi-1 1914.0 69.7 1.17 0.04 Kauhauroa-2 2131.0 69.8 1.17 0.04 Awatere-1 2136.0 69.9 1.17 0.04 Toetoe-2A, 2C 1829.0 69.9 1.17 0.04 J.D. George-1 1649.9 70.0 1.17 0.04 Parikino-1 2316.5 70.2 1.17 0.04 Kaipikari-1 1854.0 70.6 1.19 0.04 Clematis-1 1800.0 70.7 1.19 0.04 Tuhara-1B 2169.3 70.8 1.19 0.04 Matiri-1 1467.0 70.9 1.19 0.04 Kiakia-1/1A 2225.0 72.2 1.20 0.04 Upukerora-1 2009.0 72.4 1.20 0.04 Arahura-1 1736.0 72.9 1.22 0.04 Salisbury-1 2050.0 73.6 1.24 0.04 Toetoe-8 1986.0 74.6 1.26 0.04 Puniwhakau-1 2146.0 75.3 1.25 0.04 Taramakau-1 2129.0 75.8 1.27 0.04 Toetoe-9 2027.0 75.8 1.27 0.04 Te Horo-1 1829.3 76.0 1.27 0.04 Kaimiro-14, 14A 1843.0 76.4 1.27 0.04 Aratika-3 1729.0 76.8 1.29 0.04 Opoho-1 2320.0 76.9 1.29 0.04 McKee-7 2178.0 77.2 1.29 0.04 Devon-2 1883.0 77.8 1.30 0.04 Pukemai-3 2098.0 77.9 1.31 0.04 McKee-6 2227.0 78.6 1.32 0.04 Tuhua-3A, B, C 2125.0 78.8 1.32 0.04 McKee-2B 2237.0 78.9 1.32 0.04 Waitangi Station-1 2135.0 79.1 1.32 0.04 McKee-13 2278.0 80.1 1.34 0.04 Te Puia-1 2042.7 80.2 1.34 0.04 Durham-1 2303.0 80.8 1.36 0.04

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Total Depth BHT Well Name o MWt PJ (m) (C ) Pouri-2 2233.0 80.9 1.60 0.05 Tariki North-1 2431.0 81.0 1.36 0.04 J.W. Laughton-1 2135.0 81.1 1.36 0.04 Harihari-1 2527.4 81.2 1.36 0.04 McKee-2C 2316.0 81.2 1.36 0.04 Ahuroa-2 2465.0 83.1 1.39 0.04 Toetoe-2 2276.0 83.3 1.39 0.04 McKee-3 2400.0 83.6 1.41 0.04 Crusader-1A 2060.0 83.7 1.41 0.04 Pukemai-1 2293.0 83.8 1.41 0.04 Toetoe-1 2310.0 84.3 1.41 0.04 Toetoe-7 2315.0 84.5 1.42 0.04 Cape Egmont-1 2435.0 84.6 1.42 0.04 Tariki-2A 2564.5 84.6 1.42 0.04 Ruakituri-1 2745.0 85.6 1.44 0.05 Tuhua-8 2471.0 85.6 1.44 0.05 Waihapa-3 2706.0 85.9 1.44 0.05 Makuri-1, 1A 2500.0 86.4 1.44 0.05 Tauteka-1 2309.0 86.5 1.44 0.05 Tuhua-5A 2509.0 86.7 1.46 0.05 Toetoe-4A, B, C 2326.0 87.0 1.46 0.05 Tuhua-2, 2A 2529.0 87.3 1.46 0.05 Tipoka-2 2504.0 87.7 1.48 0.05 Pukemai-1A 2432.0 88.0 1.47 0.05 Tuhua-1 Re-entry 2564.0 88.3 1.47 0.05 Makara-1B 2467.0 89.0 1.49 0.05 Mangorei-1 2229.0 89.3 1.49 0.05 Whangaehu-1 3495.0 89.9 1.51 0.05 Waitaria-2 2548.1 90.2 1.51 0.05 Tariki-4, 4C 2777.0 90.4 1.51 0.05 Notown-1 2116.0 90.6 1.52 0.05 Toetoe-3 2618.0 93.5 1.58 0.05 Toetoe-5 2536.0 93.5 1.58 0.05 Stent-1 2710.0 93.7 1.58 0.05 Pukemai-2 2631.0 93.9 1.58 0.05 Hukarere-1 3213.2 94.6 1.59 0.05 Paritutu-1 2400.0 95.0 1.59 0.05 Piakau-1 2905.0 95.2 1.59 0.05 Crusader-1 2441.0 96.4 1.61 0.05 Tariki-2 3020.0 97.0 1.62 0.05 Mokoia-1 3750.0 97.1 1.62 0.05 Waihapa-6 3245.0 100.0 1.68 0.05 Oakura-1 3220.0 100.9 1.69 0.05 Tariki-1 3191.0 101.6 1.69 0.05 Ahuroa-1A 3153.0 102.1 1.71 0.05 Tariki North-1A 3209.0 102.1 1.69 0.05

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Total Depth BHT Well Name o MWt PJ (m) (C ) Rotokare-1 3232.7 102.7 1.73 0.05 Makara-1 2940.0 103.2 1.73 0.05 Toko-2 3202.0 103.4 1.73 0.05 Midhurst-1 3330.8 105.4 1.76 0.06 Hu Road-1/1A 3350.0 105.9 1.78 0.06 Happy Valley-1C 3131.4 106.0 1.78 0.06 Ahuroa-1 3326.0 106.9 1.80 0.06 Pukearuhe-1 3138.0 107.6 1.81 0.06 Burgess-1 3264.0 108.3 1.83 0.06 Cape Farewell-1 2817.0 108.9 1.83 0.06 Opoutama-1 3658.5 112.6 1.90 0.06 Waiho-1 3749.4 113.2 1.90 0.06 Wharehuia-1 3595.0 114.3 1.91 0.06 Devon-1 2868.0 116.1 1.95 0.06 Makino-1, 1AA 4100.0 116.5 1.95 0.06 Kokiri-1 3233.0 122.8 2.07 0.07 Onaero-1 3590.0 124.4 2.08 0.07 Waimamaku-2 3356.7 126.9 2.14 0.07 Manganui-2 3753.0 131.2 2.20 0.07 Pohokura South-1 3780.0 132.0 2.22 0.07 Totara-1 3965.0 132.1 2.22 0.07 Huinga-1, 1A, 1B 4373.0 133.7 2.25 0.07 Bounty-1 3131.0 134.3 2.25 0.07 Kapuni-15 4770.0 135.4 2.27 0.07 Manganui-1 3975.0 138.0 2.32 0.07 Tipoka-1, 1A 4359.0 141.6 2.39 0.08 Waihapa-1, 1A 4942.0 144.4 2.42 0.08 Ngatoro-1 4126.0 146.6 2.48 0.08 Rere-1 4351.0 149.7 2.53 0.08 Toko-1 4900.0 150.3 2.53 0.08 Cardiff-1 5064.0 152.5 2.58 0.08 Tuihu-1, 1A 4845.0 153.4 2.60 0.08 Te Kiri-1 4710.0 154.1 2.60 0.08 Inglewood-1 5061.0 164.4 2.77 0.09 New Plymouth-2 4451.6 171.9 2.91 0.09 TOTAL ENERGY 317.5 10.0

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Principal Location Other Locations

1 Fairway Drive Dunedin Research Centre Wairakei Research Centre National Isotope Centre Avalon 764 Cumberland Street 114 Karetoto Road 30 Gracefield Road PO Box 30368 Private Bag 1930 Wairakei PO Box 31312 Lower Hutt Dunedin Private Bag 2000, Taupo Lower Hutt New Zealand New Zealand New Zealand New Zealand T +64-4-570 1444 T +64-3-477 4050 T +64-7-374 8211 T +64-4-570 1444 www.gns.cri.nz F +64-4-570 4600 F +64-3-477 5232 F +64-7-374 8199 F +64-4-570 4657