GNS Science Consultancy Report 2006/0XX

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Assuming a flow of 4 L s -1 , the 206 wells with bottomhole temperatures of 30 to 120 o C can potentially produce 166,754 kWt of energy (238,220 x 0.7 = 166,754) for various direct heat uses. For the 20 wells with temperatures of 120-172 o C, the hot fluids can be used to generate power using a down hole heat pump (to enhance the flow rate and keep the resource under pressure to prevent formation of a vapour phase (Hance, 2005) and a binary cycle system. A down hole pump can be used up to about 200 o C (Hance, 2005) which is well above the highest temperatures in the abandoned wells. The total power that could be produced from these wells, assuming a flow of about 4 L s -1 and a capacity factor of 10% is 4,772 kWe (kilowatt electric) or an average of about 238 kWe per well. 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 70 mW/m 2 (>33 o C/km), outside the Taupo Volcanic Zone, Ngawha and land administered by the Department of Conservation, covers an area of about 31,520km 2 or about 12% of the New Zealand landmass (Figure 12). In these regions, a temperature of 120 o C 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 km 2 , have enough permeability where heated water circulates, the temperature of extraction is 100 o C, 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. GNS Science Report 2007/23 16
Figure 12. Map showing areas where temperatures >120 o C could be intersected at >3200m. Blue areas are under the jurisdiction of the Department of Conservation and cannot be drilled. GNS Science Report 2007/23 17
Page 2 and 3: Abandoned oil and gas wells - a rec
Page 4 and 5: CONTENTS ABSTRACT..................
Page 6 and 7: ABSTRACT There are 349 abandoned on
Page 8 and 9: Figure 1. Temperature, depth and pe
Page 10 and 11: 2.0 ABANDONED OIL AND GAS WELLS IN
Page 12 and 13: Figure 5. Map showing the distribut
Page 14 and 15: Figure 6. Drilled vertical depths o
Page 16 and 17: Figure 8. Temperatures ranges of on
Page 18 and 19: Table 1. Number of wells within a r
Page 20 and 21: 3.3 REASONS FOR ABANDONING WELLS Mo
Page 24 and 25: 5.0 CURRENT GEOTHERMAL USE OF ABAND
Page 26 and 27: In New Zealand temperature may be p
Page 28 and 29: Figure 16. Abandoned hydrocarbon we
Page 30 and 31: 10. Determine how geothermal produc
Page 32 and 33: Isaac M J, Herzer R H, Brook F J an
Page 34 and 35: APPENDIX 1 NOTES ON THE GEOTHERMAL
Page 36 and 37: Speaker Company/Agency Topic Main P
Page 38 and 39: Table 6. Basic well data for onshor
Page 40 and 41: Well Name NORTH ISLAND TARANAKI Dat
Page 42 and 43: Well Name SOUTH ISLAND WEST COAST D

GNS Science Consultancy Report 2006/0XX

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