Abandoned Oil and Gas Wells a Reconnaissance Study of an Unconventional Geothermal Resource

Abondoned oil and gas wells a reconnaissance study of an unconventional geothermal resource A. G. Reyes

GNS SCIENCE REPORT 2007/23 July 2007

Abandoned oil and gas wells a reconnaissance study of an unconventional geothermal resource A. G. Reyes

GNS Science Report 2007/23 July 2007

GNS Science

BIBLIOGRAPHIC REFERENCE Reyes A.G. 2007. Abandoned oil and gas wells – a reconnaissance study of an unconventional geothermal resource, GNS Science Report 2007/23 41 p.

A. G. Reyes, GNS Science, 1 Fairway Drive, Avalon, PO Box 30368, Lower Hutt

© Institute of Geological and Nuclear Sciences Limited, 2007 ISSN 1177-2425 ISBN 978-0-478-09988-1

CONTENTS ABSTRACT.............................................................................................................................................iii KEYWORDS ...........................................................................................................................................iii 1.0

INTRODUCTION .........................................................................................................................1 1.1 1.2

Geothermal Resources in New Zealand ....................................................................... 1 Objectives of Study........................................................................................................ 2

2.0

ABANDONED OIL AND GAS WELLS IN OTHER COUNTRIES ..............................................4

3.0

ABANDONED OIL AND GAS WELLS IN NEW ZEALAND ......................................................4 3.1 3.2 3.3

4.0

Distribution and Dates of Completion............................................................................ 4 Well Depths and Estimated Bottom hole Temperatures ............................................... 7 Reasons for abandoning wells .................................................................................... 14

HARNESSING GEOTHERMAL ENERGY FROM ABANDONED HYDROCARBON WELLS14 4.1 4.2

Geothermal Potential Projections................................................................................ 14 Sedimentary basins and other areas outside the Taupo Volcanic Zone..................... 16

5.0

CURRENT GEOTHERMAL USE OF ABANDONED HYDROCARBON WELLS....................18

6.0

INITIAL STEPS FOR USE OF WELLS ....................................................................................20

7.0

RECOMMENDATIONS FOR FUTURE WORK ........................................................................23

8.0

SUMMARY AND CONCLUSIONS ...........................................................................................24

9.0

ACKNOWLEDGMENTS ...........................................................................................................25

10.0

REFERENCES ..........................................................................................................................25

FIGURES Figure 1

Temperature, depth and permeability ranges of conventional and unconventional sources of geothermal energy in New Zealand.................................................................2

Figure 2

Distribution of conventional and unconventional geothermal resources in New Zealand..............................................................................................................................3

Figure 3

Distribution of offshore and onshore abandoned wells in various hydrocarbon basins. ...5

Figure 4

Number of offshore and onshore abandoned wells in hydrocarbon basins and nonbasins of New Zealand. .....................................................................................................5

Figure 5

Map showing the distribution of abandoned oil and gas wells with date of drilling completion and the general location of sedimentary basins..............................................6

Figure 6

Drilled vertical depths of abandoned onshore hydrocarbon wells.....................................8

Figure 7

Estimated bottom hole temperatures in abandoned onshore hydrocarbon wells. ............9

Figure 8

Temperature ranges of abandoned oil and gas wells .....................................................13

Figure 9

Depth vs estimated bottom hole temperatures of offshore and onshore abandoned hydrocarbon wells and possible geothermal uses...........................................................14

Figure 10

Depth vs formation pressure in Taranaki wells ...............................................................17

Figure 11

Possible geothermal uses of abandoned hydrocarbon wells. .........................................15

Figure 12

Map showing areas where temperatures >120oC could be intersected at >3200m........17

Figure 13

Direct heat use of 29oC waters from well Bonithon-1, New Plymouth.............................18

Figure 14

A. Bonithon-1 in New Plymouth B. Kotuku borehole forming a pseudo-warm spring. ...18

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Figure 15

Distribution of abandoned onshore hydrocarbon wells in Taranaki showing (A) vertical depths and (B) estimated bottomhole temperatures with roads and population centres. ............................................................................................................................21

Figure 16

Abandoned hydrocarbon wells in Taranaki (squares) that may be converted for geothermal use.. ..............................................................................................................22

TABLES Table 1

Number of wells within a range of temperatures .............................................................15

Table 2

Potential energy from wells .............................................................................................16

Table 3

Potential energy from drilling new wells in high heat flow regions ..................................22

Table 4

Proposed wells for a 0.5 to 1 MWe pilot geothermal plant in Taranaki ...........................23

Table 5

Main points of presentations during the Oil and Gas conference held in March 2006....29

Table 6

Basic well data.................................................................................................................32

APPENDICES Appendix 1 Notes on the Geothermal Energy Generation in Oil and Gas Settings Conference .......27 Appendix 2 Abandoned onshore hydrocarbon wells in New Zealand ................................................31

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ABSTRACT There are 349 abandoned onshore oil and gas wells in New Zealand that can potentially be harnessed for geothermal energy for direct usage of heat, power production and development as pseudo hot spring systems for tourism. Well depths range from 17 to 5064m vertical. Estimated bottom hole temperatures range from ambient temperatures (about 12 to 18oC) to 172oC. Of these wells 65% are located in the North Island, the rest in South Island. Taranaki, the only oil and gas producing hydrocarbon basin in the country, has the largest number of abandoned oil and gas wells at 140 or about 40% of all onshore wells. The use of abandoned hydrocarbon wells for direct heat utilisation and power generation could add another 6.1 PJ to the geothermal energy potential of New Zealand. Of these 1.4 PJ is for use with ground source heat pumps from 123 wells with bottomhole temperatures of 3500m depths. At shallow depths and temperatures of 10-35oC heat can be harnessed from the ground or circulating water in boreholes or warm water in abandoned mines using ground source heat pumps (Lund et al, 2005). In Central and Northern Europe, for example, all heat energy stored below about 15m from the surface is considered geothermal energy (Rybach and Sanner, 2000). For some of the unconventional sources of geothermal energy, such as heat from sedimentary basins and hot dry rock (HDR), permeability or the volume of circulating fluids may be too low to economically extract heat. To increase the productivity and lifetime of these marginal geothermal sources for power generation, enhanced or engineered geothermal systems (EGS) technology may be required where, essentially, low permeability hot rock at depth is artificially fractured and fluid is introduced into the newly-fractured rock where it is heated by conduction. The heated fluids are recirculated to the surface by pumps and the heat extracted by a heat exchanger (e.g. Smith, 1983; White, 1983). 1.1

GEOTHERMAL RESOURCES IN NEW ZEALAND

There are conventional and non-conventional sources of geothermal energy for power generation and direct heat utilisation in New Zealand (Figure 1) ranging in temperature from about 12 to 15oC at about 15m to as high as >330oC at >3,500m. Power can be generated by steam turbines or by binary cycle systems using the Organic Rankine Cycle (ORC) where the working organic fluid has a low boiling temperature such as isopentane, or the Kalina Cycle which uses ammonia/water. The newest system is called the NE (Natural Energy) Engine that operates on hot and cold water and uses liquid CO2 as a working fluid in the heat exchanger engine (www.fossil.energy.gov). Conventional sources include (1) high enthalpy hot spring systems in the Taupo Volcanic Zone (TVZ) and Ngawha in Northland some of which are now harnessed for power production, (2) waste-water from high enthalpy power-generating systems such as Wairakei, Mokai, Ohaaki-Broadlands, Kawerau, Rotokawa and Ngawha and (3) hot spring systems outside the Taupo Volcanic Zone and Ngawha and including springs in the North Island, islands in the Bay of Plenty and Hauraki Gulf and in the South Island (Figure 2). Nonconventional sources of geothermal energy include: (1) most of the TVZ outside high enthalpy geothermal systems, where thermal gradients range from 40oC/km to >50oC/km but permeability low, (2) 12oC to 170oC waters in abandoned oil and gas (hydrocarbon) wells, (3) heated waters in abandoned flooded coal and mineral mines, (4) conductive heat from shallow depths (70 mW/m2) sedimentary basins, metamorphic terrain and rapidly rising regions of the country such as the Raukumara Peninsula (Mazengarb and Speden, 2000) and the Southern Alps (Allis and Shi, 1995) and regions outside high heat flow regions. The location of some of the nonconventional heat sources available in New Zealand are shown in Figure 2.

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Figure 1. Temperature, depth and permeability ranges of conventional and unconventional sources of geothermal energy in New Zealand. The temperature and depth range of abandoned oil and gas wells in New Zealand are highlighted in red.

Geothermal energy in this country is associated with power generation in the Taupo Volcanic Zone and Ngawha where volcanism is recent. New Zealand has a total installed power generating capacity of 435 MWe provided by six geothermal systems in the Taupo Volcanic Zone and one at Ngawha in Northland, where a binary plant produces 9 MWe (http://www.crownminerals.govt.nz). The installed capacity for direct usage of geothermal energy in the country is 448 MWt (White, 2006), 62% of which is produced from waste water and waste steam or dedicated wells in the power-generating Kawerau, Mokai, Ohaaki-Broadlands and Wairakei geothermal systems. About 170 MWt is used for bathing in more than 30 commercial swimming pools and in ad hoc holes dug for hot water at the edges of rivers or at tide level along the sea shore, space-heating, fruit irrigation, plant or fish cultivation, and health and beauty therapy. 1.2

OBJECTIVES OF STUDY

This is reconnaissance study on the potential of extracting geothermal energy from abandoned oil and gas wells and regions outside the Taupo Volcanic Zone (TVZ) and Ngawha. Assumptions are broad and conservative, calculations are basic.

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Figure 2. Distribution of conventional and nonconventional geothermal resources in New Zealand including hot springs, abandoned oil and gas wells, abandoned flooded underground coal and mineral mines and stored heat in the rock. Conductive heat flow contours are from Allis et al, 1998.

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2.0

ABANDONED OIL AND GAS WELLS IN OTHER COUNTRIES

The idea of using abandoned oil and gas (hydrocarbon) wells and drilling wells in sedimentary basins to produce geothermal energy is not new. Low enthalpy geothermal resources in sedimentary basins in France have been tapped by wells for district heating since 1969. At present there are 41 plants in the Paris basin including 15 in the Aquitane basin and five in other regions producing hot water for a total of 200,000 households and supplanting about 170,000 TOE (Laplaige et al, 2000). Albania, Poland, Germany, Switzerland, USA, France and Australia are exploring the possibility of recovering heat from hydrocarbon wells (e.g., Bodvarrsson and Reistad, 1983; White, 1983; Barbacki, 2000; Schellshmidt et al, 2000; Lund et al, 2005). In the USA abandoned hydrocarbon wells, in regions of high heat flow (>75 mW/m2) and sufficient water flow such as Texas and Oklahoma, are estimated to have a power generating potential at the gigawatt level (Appendix 2). Using the existing wells minimises the initial costs of geothermal power production. The main capital funding input is fitting existing wells with heat exchangers and small power plants (McKenna et al, 2005). In March 2006, the Southern Methodist University in Texas held the first conference on the potential of harnessing geothermal power from abandoned hydrocarbon wells (Appendix 1).

3.0

ABANDONED OIL AND GAS WELLS IN NEW ZEALAND

Although the number of abandoned hydrocarbon wells in New Zealand is 50oC in more than 150 wells drilled to depths >625m, (2) the presence of nonsaline or saline waters in most of the abandoned wells that may be discharged using artesian pressures inherent in the wells or through downhole pumps, (3) over pressuring in some wells in Taranaki (King and Thrasher, 1996), the East Coast (Field et al) and Northland (Isaac et al) indicate that some wells are artesian and will flow without the need for well stimulation or hydrofracturing, (4) mud losses during drilling indicate permeability in several wells e.g., Kiakia-1/1A in the East Coast, and (4) large areas of high heat flow cover parts of the Northland, Taranaki, Wanganui and East Coast basins in the North Island and parts of the West Coast basin of the South Island (Figures 2 and 3) where the surface conductive heat flow of >70 mW/m2 indicate thermal gradients of >33oC/km. 3.1

DISTRIBUTION AND DATES OF COMPLETION

There are about 450 onshore and offshore abandoned hydrocarbon wells in New Zealand (Figure 3). Of these wells, 349 are onshore with the offshore wells drilled mostly in waters 3km depths (Figure 6.12 of King and Thrasher, 1996)

4.0

HARNESSING GEOTHERMAL ENERGY FROM ABANDONED HYDROCARBON WELLS

4.1

GEOTHERMAL POTENTIAL PROJECTIONS

As shown in Figures 9 and 11 geothermal energy from abandoned oil and gas wells can be harnessed for direct heat using ground source heat pumps at temperatures of about 120oC and sufficient water flow can potentially be used for power generation. There are 123 onshore wells with bottomhole temperatures 33oC/km), outside the Taupo Volcanic Zone, Ngawha and land administered by the Department of Conservation, covers an area of about 31,520km2 or about 12% of the New Zealand landmass (Figure 12). In these regions, a temperature of 120oC will be intersected at about 2,600m in Northland and the Coromandel and at least 3,200m in the rest of the North Island and in South Island (Figures 2 and 12; Table 3). Drilling new wells in these areas is dependent on accessibility (access factor) dictated by topography (e.g., slip-prone rugged Alpine slopes are problematic), land usage (e.g., national parks, private property, Maori-owned may not be accessible for drilling) and geology (e.g. proximity to faults may contribute to permeability at depth and are therefore attractive for drilling; areas best drilled for coal, hydrocarbons or precious metals may not be immediately accessible for deep drilling; regions with swelling clays or highly silicified rocks may cause drilling problems). The success rate of 0.40, used in Table 3, is the lowest success rate in exploration geothermal drilling in New Zealand, based on the percentage of geothermal wells that would successfully produce 1 MWe per five wells drilled (Barr et al, 1984). Assuming that the areas to be drilled, at 2 wells/100 km2, have enough permeability where heated water circulates, the temperature of extraction is 100oC, and the drilled wells will have a flow of at least 4 L s-1 then another 21,100 kWe can be potentially produced or 0.67 PJ of geothermal energy generated (Table 3). However, before drilling new deep wells in high heat flow regions outside the Taupo Volcanic Zone and Ngawha, geothermal energy from existing abandoned hydrocarbon wells should be explored first.

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Figure 12. Map showing areas where temperatures >120oC could be intersected at >3200m. Blue areas are under the jurisdiction of the Department of Conservation and cannot be drilled.

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5.0

CURRENT GEOTHERMAL USE OF ABANDONED HYDROCARBON WELLS

In Taranaki, warm bicarbonate water (27oC) from the 910m deep Bonithon-1, an abandoned hydrocarbon well drilled in 1908, is heated to 33-38oC by gas and fed into the therapy and private pools of a commercial spa enterprise. The bore water is also bottled and sold as therapeutic mineral water (Figure 13). In Kotuku, West Coast, a leaking hydrocarbon well discharged 21oC (ambient temperature=13oC) effervescent bicarbonate waters at 3 kg s-1 for years and formed a pseudo warm spring pool that could be used as a tourist attraction (Figure 14). However in early 2006 the well ceased to flow due probably to sealing by carbonate deposition and the lowered water level caused by drought in the region. A warm spring in Lake Omapere, Northland was also originally a well. These examples show that it is possible to harness abandoned hydrocarbon wells for direct utilisation of heat or turn them into “pseudo hot springs” for tourism. Despite the projections of extracting gigawatts of geothermal power from abandoned hydrocarbon wells in the Gulf regions of the USA, only one hydrocarbon well is producing 1.5 MWe of geothermal power, located in a geopressured sedimentary basin in Pleasant Bayou, Louisiana (Campbell and Hattar, 1990; Griggs, 2005). The well is 5030m deep, and intersected a leaky fault, a fault that leaks due to pressure differentials in the reservoir. Wellhead pressure is 20.7 MPa. Fluids contain 87% CH4. The hybrid cycle power plant is equipped with a pressure reduction turbine, with the gas providing 690 kW, the binary cycle turbine 535 kW and a parasitic load of 270 kW. Problems with corrosive saline solutions were solved by using 16 gauge steel; scaling problems from 130,000 mg/kg TDS waters by using inhibitors, and carbon fouling by regularly shutting and opening the plant (www.smu.edu/geothermal/Oil&Gas/Oil&Gas_SMUmeeting_summary; Appendix 1).

Figure 13. Direct heat use of 29oC waters from well Bonithon-1, New Plymouth

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Figure 14. Kotuku borehole forming a pseudo-warm spring (21oC) in 2003. Flow is 3 kg/s (photo by A.G.Reyes).

18

2

o

2

1,610 3,245 31,520

18,800

33

40 40

7,865

Area in km2

33

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Coromandel Northland TOTAL

North Island South Island

Region

Thermal gradient (oC/km)

100 100

100 100

120oC 2,600m 120oC o 120 C

Temperature of extraction (oC)

3,200m 120oC

Temperature at depth

419 419

419

419

Enthalpy (kJ/kg)

4 4

4

4

Flow (kg/s)

32 65

376

157

2 wells/100 km2

0.4 0.4

0.4

0.4

Success

6 13 125

75

31

No. of wells for power generation

10,793 21,754

126,035

52,727

kW

1,079 2,175 21,131

12,604

5,273

kWe (0.1 CF)

34 69 667

398

166

TJ

19

0.03 0.07 0.67

0.40

0.17

PJ

Table 3. Drilling new wells in regions with heat flow >70 mW/m where the geothermal gradient is >33 C/km. Two wells are proposed for each 100 km area. One is for production, the other for reinjection. CF= conversion factor

In New Zealand temperature may be present but there are many technical and non technical problems to be considered when converting oil and gas wells for geothermal extraction e.g., 1. Marginal permeability and fluid flow in a number of oil and gas wells may require hydrofracturing and/or well stimulation, 2. The state of the casing and grouting jobs of wells drilled before 1980, which comprise about 45% of the onshore wells, may not be satisfactory and the wells not usable, 3. Wells are filled and plugged when abandoned and will require drilling out the fills and cement before use, 4. Some wells may be difficult to locate because all surface traces are covered (Funnell, pers comm. 2007), 5. Oil fouling of geothermal turbines is possible when producing some wells for geothermal power, 6. Liner tubings may need to be converted to slotted liners (or the tubings perforated), 7. Liners have either been pulled out or not installed at all and rock may have caved-in in some wells, 8. Casing corrosion, whether internally or externally induced, is probable, 9. Access to the wells owned by oil companies, Maori tribes, other private owners or the New Zealand government, 10. Acceptance and support of the government to the idea of converting hydrocarbon wells for geothermal use. In Taranaki cogeneration and colocation of geothermal and hydrocarbon energy sources may affect reinjection strategies because water reinjection may hasten water flooding in structurally or stratigraphically-connected hydrocarbon-bearing zones in nearby producing gas and condensate wells. Other factors that should be considered include finding methods of stimulating water flow in abandoned oil and gas wells, determining the type of binary cycle system to be used (Rankine, Kalina or NE Engine) and the feasibility of using hybrid power plant systems to cogenerate power from geothermal fluids and methane from the same well, and later, investigating EGS (Enhanced or Engineered Geothermal Systems) technology to exploit deep oil and gas wells.

6.0

INITIAL STEPS FOR USE OF WELLS

A pilot plant could be set up in Taranaki to demonstrate the viability of this hydrocarbon-togeothermal energy scheme. Taranaki has the most number of abandoned hydrocarbon wells with some of the highest estimated bottom hole temperatures and artesian pressures below 3000m (Figures 15A and B). It is the centre of oil, gas and petrochemical production in the country. It is one of the most energy-hungry regions of the country that could benefit from cogeneration and colocation of hydrocarbon and geothermal energy sources to support its dairying, horticultural and food processing industries. Low temperature wells could be harnessed to provide heat for space heating of dairy farm buildings, milk pasteurisation, greenhouses, swimming pools and spas. Higher temperature wells (16 wells) can be used for power generation.

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The 16 high temperature wells selected for possible geothermal power generation (Figure 15) have estimated bottom hole temperatures 120oC to 172oC, drilled to >3100m and are mostly artesian. However four of these (with yellow crosses) were drilled prior to 1980 and the state of the casing, liners and grouting jobs is uncertain and need to be examined. All 16 wells have been plugged with cement upon abandonment. For a binary cycle pilot plant with a capacity of about 200 kW five wells were selected based on their bottomhole temperatures, proximity to a population centre or an industrial complex such as Fonterra and proximity to another abandoned well that can be possibly used as a reinjection well. These wells include Tipoka-1, Te Kiri-1, Toko-1, New Plymouth-2 or Inglewood-1 (Table 4), listed according to priority, and shown in Figure 16. A downhole pump may be needed in some wells to increase or sustain fluid flow. Electricity generated from Tipoka-1 or Te Kiri-1 can be used by nearby dairy farms or Fonterra while other wells such as from Toko-1, New Plymouth-2 and Inglewood-1 may supplement electricity from the grid for Stratford, New Plymouth and Inglewood, respectively. Other wells with bottomhole temperatures >120oC near Stratford are Wharehuia-1, Piakau-1 and Waihapa-1. Another well that could be harnessed in Inglewood is Tauteka-1. Cardiff-1, a well with a bottomhole temperature of 153oC may be reactivated as a source of hydrocarbons and hence not included in the list. More geoscientific studies need to be done on these wells before any power harnessing could be done. The effect of drawing out large volumes of hot water on nearby activelyproducing hydrocarbon wells is not known.

A

B

Figure 15. Distribution of abandoned onshore hydrocarbon wells in Taranaki showing (A) vertical depths and (B) estimated bottomhole temperatures with roads and population centres. Haloed wells may be used for geothermal power production.

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Figure 16. Abandoned hydrocarbon wells in Taranaki (squares) that may be converted for geothermal use. All o plotted abandoned hydrocarbon wells have estimated bottom hole temperatures (BHT) >120 C and depths from 3131 – 5064m.

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Table 4. Proposed wells for 200 kWe pilot geothermal plant in Taranaki. Refer to Appendix 3 for well details. BHT= bottom hole temperature. Well

Priority

Estimated

Comments

kWe o

Tipoka-1

1

240

Tipoka-1 fluids (BHT= 142 C at 4360m) can be reinjected in Tipoka-2, o 1.1 km away, which has BHT= 88 C at 2504m. Power can be used by nearby dairy farms.

Te Kiri-1

2

260

o Well (154 C at 4710m) near dairy farms associated with Fonterra. There may be a need to drill a nearby reinjection well

250

Fluids from Toko-1 with BHT=150oC at 4900m can be reinjected into o Toko-2 with BHT = 103 C at 3200m, 1.2km away. There is a seal between the Mangahewa Fm in Toko-1 and the shallower Tikorangi Fm in Toko-2. Power can be used for Stratford. Other wells near Stratford that can be used for power generation are: Wharehuia-1 o (114 C at 3595m) with fluids reinjected into Piakau-1 1.0km away or Waihapa-1 (144oC at 4942m) using Waihapa-2, 1.8km away, as a reinjection well

290

Highest BHT of all onshore wells at 172oC; located in middle of New Plymouth. Fluids can be reinjected in numerous adjacent abandoned wells. This was drilled before 1980 and the state of the casings and grouts is unknown.

275

BHT= 164 C at 5061m. This was drilled before 1980. There may be a need to drill a nearby reinjection well. The nearest abandoned well that could be used for reinjection is Ngatoro-1 about 2.1km away. Power can be used by Inglewood. Another well near Inglewood is o Manganui-1 (131 C at 3753m) with Tauteka-1, 830m away, as a reinjection well

Toko-1

3

New Plymouth2

4

o

Inglewood-1

7.0

5

RECOMMENDATIONS FOR FUTURE WORK

This is merely a reconnaissance study whose main goal is to present an idea and the basic data of wells that could be used for geothermal energy purposes. Before any wells could be used the following studies should be done: 1. Review all literature on wells regarding water reservoirs, fault and stratigraphic permeability, stratigraphic connectivity among abandoned and actively-producing wells, downhole pressure and temperature measurements and geology. 2. Determine the state of the casing/tubings, liners and cementing jobs of selected wells. 3. Determine the corrosion state of the well pipes. 4. Measure downhole temperatures of selected wells. 5. Determine flow rates of well discharges and methods of stimulating water flow. 6. Find out if hydrofracturing is necessary or possible to enhance permeability. 7. Find out the maximum working temperatures of down hole pumps. 8. Determine fluid discharge chemistry to find out if a hybrid plants can be used to tap both gas and geothermal fluids, predict fouling problems to the plant, determine ways of disposing well fluids (use a reinjection well or dispose fluids into the waterways?). 9. Determine fluid pathways and temperatures using petrological and geochemical methods. GNS Science Report 2007/23

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10. Determine how geothermal production will affect the hydrocarbon reservoirs. 11. Study the economic viability of converting extant hydrocarbon wells for geothermal direct heat use or for power production.

8.0

SUMMARY AND CONCLUSIONS

The 349 abandoned onshore oil and gas wells in New Zealand have total vertical depths of 17 to 5064m and estimated bottom hole temperatures ranging from ambient temperatures (about 12 to 18oC) to 172oC. Of these wells 65% are located in the North Island, the rest in South Island. Taranaki, the only oil and gas producing hydrocarbon basin in the country, has the largest number of abandoned oil and gas wells at 140 or about 40% of all onshore wells and also contains 16 of the 20 wells with bottomhole temperatures >120oC. Thus the use of abandoned hydrocarbon wells for direct heat utilisation and power generation could add another 6.1 PJ to the geothermal energy potential of New Zealand. Of these 1.4 PJ is for use with ground source heat pumps from 123 wells with bottomhole temperatures of 120oC and include, with decreasing priority, Tipoka-1, Te Kiri-1, Toko-1, New Plymouth-2 or Inglewood-1. The selected wells are either near dairy farms or an industrial complex like Fonterra or within a population centre such as Stratford, new Plymouth and Inglewood. Three of the sites are within a 1.8 km radius from another abandoned well, but with lower temperatures, that can be used for reinjection. Well Inglewood-1, however, is 2.1 km from the nearest abandoned well and a reinjection may need to be drilled nearer the well and there is no nearby well for Te Kiri-1. New wells in high heat flow regions of the country, outside the Taupo Volcanic Zone, Ngawha and Department of Conservation land, may provide another 0.67 PJ of energy assuming production of energy from waters extracted at 100oC and a flow of about 4 L s-1. However, these will only be drilled once the viability of geothermal power outside the Taupo Volcanic Zone and Ngawha have been proven by harnessing geothermal energy from abandoned hydrocarbon wells. The requisite temperature may be present in abandoned hydrocarbon wells for a wide range of geothermal energy uses but there are many geoscientific, technical and non technical problems to be considered before oil and gas wells can be used for geothermal power generation or cogeneration of geothermal and hydrocarbon energy. However New Zealand has the available expertise in the geothermal and oil and gas industries and access to the requisite technology, making this scheme of converting old hydrocarbon wells for geothermal use viable.

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Converting at least a pair of abandoned hydrocarbon wells (one for production the other for reinjection) in Taranaki for use in a 200 kWe pilot plant may prove the viability of this scheme.

9.0

ACKNOWLEDGMENTS

Thank you to D. Darby and E. Mroczek for reviewing the report whose comments and suggestions have contributed to the improvement of the report. Discussions with D. Darby, E Mroczek, and J. Callan and speakers of the conference on Geothermal Energy Generation in Oil and Gas Settings Conference held in the Southern Methodist University, Texas in 13-14 March 2006 have helped in writing this report. Thank you to K. Hunt for her expert word processing.

10.0

REFERENCES

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APPENDIX 1 NOTES ON THE GEOTHERMAL ENERGY GENERATION IN OIL AND GAS SETTINGS CONFERENCE

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APPENDIX 1 NOTES ON THE GEOTHERMAL ENERGY GENERATION IN OIL AND GAS SETTINGS CONFERENCE The conference was held in March 2006 at the Southern Methodist University (SMU) in Texas, organised by D. Blackwell. The main point of the conference is the enormous potential of oil and gas settings in providing geothermal power. What oil and gas operators view as the death of a fossil fuel system is viewed as the source of another energy by the geothermal industry that also has the blessings of the environmentally conscious population. Talks were about 75% technical, 25% laws and regulations affecting geothermal and oil and gas systems in the USA (main points of talks are in Table 4). The most interesting talks and posters were centred on the heat flow map of the USA that SMU had published at the AAPG. The map making was led by David Blackwell of SMU. One of the main offshoots of this map is the reestimation of the geothermal potential of the USA using oil and gas wells and EGS technology (EGS= Enhanced or Engineered Geothermal Systems). The total conservative geothermal potential of the USA is 43,617,976 MWe. At present geothermal provides 8900 MWe of power to 24 countries world-wide. The oil and gas operators view water flooding as the end of the field whereas geothermal operators see this phenomenon as the start of a new source of energy. Some of the problems in harnessing geothermal energy from oil and gas wells are not technical but include the lack of communication between people in the oil and gas and geothermal industries and the lack of overt support from the federal government. During the meeting the discussion panel decided to write a one-page white paper report on “Geothermal Energy Generation in Oil and gas Settings”, to be submitted to the government and oil and gas operators. Interestingly, the convenors sent nearly 15,000 invitations to oil and gas operators and technical people, government officials and the media to attend this conference (which is the first in the world and quite important for the future energy outlook of the USA, at least) but there were only 90 attendees, 80oC including overpressured systems: 43,617,976 MWe @20% recovery, using ORC and conventional steam turbines (lots of very conservative assumptions in calculations)

DOE’s geothermal budget for 2007: $0.00 yet they plan to have 40,000 MWe from geothermal by 2040 at