Three-dimensional Modeling of Injection Induced Thermal Stresses with an Example from Coso

Poro-mechanical, thermal, and chemical processes can play a significant role when developing enhanced geothermal systems. These processes occur on various time scales and the significance of their interaction varies with the problem of interest. Of particular importance is the thermo-mechanical coupling during injection operations (time scale of months/years). In fact, the phenomena of the variation of injectivity with injection water temperature and reservoir seismicity can be attributed to thermal stresses. In this paper a three-dimensional integral equation formulation is presented for calculating thermally induced stresses associated with cooling of a fracture in a geothermal reservoir. The procedure is then implemented in a computer program and is used to treat the problem of injection into an infinite fracture. The thermally induced stresses are calculated using actual field data for an injection experiment. The resulting calculations are found to be consistent with those based on a semi-analytical solution as well as field observations.