Parametric analysis of factors affecting injection and production in geothermal reservoirs
A program was designed to allow the study of the effects of several parameters on the injection of water into and production of fluid from a fractured low porosity geothermal reservoir with properties similar to those at The Geysers. Fractures were modeled explicitly with low porosity, high permeability blocks rather than with a dual-porosity formulation to gain insight into the effects of single fractures. A portion of a geothermal reservoir with physical characteristics similar to those at the Geysers geothermal field was constructed by simulating a single fracture bounded by porous matrix. A series of simulation runs were made.using this system as a basis. Reservoir superheat prior to injection, injection temperature, angle of fracture inclination, fracture/matrix permeability contrast, fracture and matrix relative permeability, and the capillary pressure curves in both fracture and matrix were varied and the effects on production were compared. Analysis of the effects of these parameter variations led to qualitative conclusions about injection and production characteristics at the Geysers. The degree of superheat prior to water injection was found to significantly affect the production from geothermal reservoirs. A high degree of superheat prior to injection increases the enthalpy of the produced fluid and causes the cumulative produced energy to nearly equal that from a reservoir which began injection much earlier. Injection temperature was found to have very little effect on production characteristics. Angle of fracture inclination affects the enthalpy of the produced fluid. Fractures dipping toward the production well allow greater flow of water toward the producer resulting in lower enthalpies of produced fluid. The fracture/matrix permeability contrast was shown to influence the production in an expected way: The lower the contrast, the lower the production rate, and the lower the enthalpy of the produced fluid at a given time. Results obtained by varying relative permeability show that the relative permeability curves used have little effect on the production from the reservoir. This indicates that the transfer between the matrix and the fracture is dominated by capillary forces, thus reducing the importance of the shape of the relative permeability curve. Capillary pressure curves were shown to have a strong effect on production characteristics, further emphasizing the importance of capillary forces in Geysers-type geothermal reservoirs.
- Research Organization:
- Stanford University, Stanford, CA; Idaho National Engineering Laboratory (INEEL), Idaho Falls, ID
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 888891
- Report Number(s):
- SGP-TR-145-8
- Resource Relation:
- Conference: Proceedings, eighteenth workshop on geothermal reservoir engineering, Stanford University, Stanford, CA, January 26-28, 1993
- Country of Publication:
- United States
- Language:
- English
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