Geothermal reservoir engineering research in New Zealand: A simplistic model and the Wairakei geothermal reservoir
Although nowadays much of the New Zealand geothermal reservoir research effort is still being concentrated on the older fields of Wairakei and Broadlands there has been a definite advance over recent years in our approach to the studies. On the practical side, long term reinjection trials are now in progress at Broadlands, and drilling, for field evaluation, is well underway at Ngawha, a field characterized by a steam discharge coupled with a hydrostatic pressure gradient. On the theoretical side, well pressure transient analysis and reservoir behavior modeling are probably the primary interests. For the former both multi-element computer modeling programs and two-phase pressure diffusion analysis (Grant, 1978, Grant and Sorey, 1979) are being used by M.A.Grant, E.Bradford and F.Sutton (AMD*) and M.L.Sorey (PEL). Geometry and boundary influences are dominant and estimated steam flows are higher than are consistent with the Corey (1954) expressions for relative permeability. Both of these effects are probably due to the fracture permeability of the reservoirs. A.McNabb (AMD) is currently taking this into account by determining the response to discharge in a fracture-block medium. He is working with 100 meter blocks, consistent with data from lumped parameter models and from well records, with a block permeability of 10{sup -15} m{sup 2}. Reservoir behavior modeling is probably the research area of greatest current interest with most research groups here involved to some extent. The models range over a wide spectrum, from extreme simplification to sophisticated detail. At the simpler extreme is the model of J.Elder (AU). This consists of two resistors and a condenser in electrical analog form but is coupled with models of the well system and the above surface plant to enable overall system effects and interactions to be assessed.
- Research Organization:
- Physics and Engineering Laboratory, Department of Scientific and Industrial Research, Lower Hutt, NZ
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 892115
- Report Number(s):
- SGP-TR-30; CONF-781222-5
- Country of Publication:
- United States
- Language:
- English
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Reservoir engineering of Wairakei geothermal field