| Abstract |
Some fundamental mechanisms associated with cooling/heating of the rock in the context of drilling and reservoir stimulation in enhanced geothermal systems are described. The role of temperature and pore pressure in wellbore failure and fracture width is considered us-ing analytical and boundary element models. Results indicate that cooling induces a pore pressure drop inside the formation that tends to increase the e .ective stresses near the well-bore but, it reduces the total stresses in the rocknearthe well more significantly (decreas-ing the stress di .erence, i.e., MohrÃs circle ra-dius). Thus, cooling causes wellbore stabil-ity with respect to shear failure and insta-bility with respect to tensile failure. Con-sequently, one often observes tension cracks whereas compressional wellbore breakouts may be absent. The cooling mechanism is useful in stimulation by cold fluid injection to enhance fracture permeability. Cooling increases joint aperture and the stress intensity at the frac-ture tip leading to crack growth. As a re-sult, fracture slip may occur leading to per-meability enhancement. On the other hand, increased pore pressure in the rock matrix re-duces fracture width. |