Analysis Of The Response Of Geothermal Reservoirs Under Injection And Production Procedures

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract A major problem facing geothermal operations is the disposal of large quantities of relatively cool waste geothermal waters. Environmental regulations may require reinjection into the reservoir. Since the reservoir is thus cooled around the injection wells, there is some reluctance to reinject into wells that might be used for future production. production. In this paper the response of a liquid-dominated geothermal reservoir to injection and production from a single well is studied. Different production from a single well is studied. Different injection-production schemes are analyzed to explore how to minimize temporary cooling around the injection well and to optimize thermal recovery. The pressure response is also calculated, and found to be affected significantly by temperature-dependent viscosity variations. This will have implications on well-test methods for geothermal reservoirs. Vertical consolidation of the geothermal system during fluid withdrawal is also discussed, showing the need to establish previous stress history before attempting to previous stress history before attempting to predict the reservoir deformation. predict the reservoir deformation. The transport of heat and fluid through a porous reservoir is computed using a numerical porous reservoir is computed using a numerical model developed at the Lawrence Berkeley Laboratory. The one-dimensional consolidation theory of Terzaghi has been coupled to the heat and fluid flow to calculate reservoir compaction. attempt is made to model chemical reactions or precipitation that might occur when waters of a precipitation that might occur when waters of a different temperature and salinity are injected into the reservoir. A. Introduction A major problem facing geothermal energy development is the disposal of large quantities of relatively cool waste geothermal waters. Operators are reluctant to reinject these fluids as they could irreversibly cool the reservoir around the injection wells and affect nearby producing wells. Gringarten and Sauty used a two-dimensional semianalytical model to investigate the effect of reinjection wells on neighboring producing wells. Tsang, and Witherspoon used the same model to suggest the screening effect that may be found in a multiple-well system. However, this model assumes a steady fluid-flow field, neglects gravity and, even more important, ignores the dependence of parameters (such as viscosity and density) on temperature variations. Thus a detailed understanding of the behavior of a geothermal reservoir cannot be expected with this semianalytic approach. Realistic two- or three-dimensional numerical models have been developed to analyze liquid-dominated geothermal systems (Mercer and Pinder; Pritchett et al.; Sorey, and others). Pritchett et al.; Sorey, and others).