Temperature Dependent Rock Fracturing in Boreholes

The paper describes a recent numerical code development and laboratory investigations on coupled thermal-mechanical processes of rock fracture propagation. A series of laboratory tests were conducted on rock strength and fracture toughness within a temperature range from -80C to 400C, and key temperature dependent parameters were obtained on granite specimens. The numerical development is based on a fracture mechanics code FRACOD that has previously been developed by some of the authors of this paper. The code simulates complex fracture propagation in rocks governed by both tensile and shear mechanisms. For the latest development an indirect boundary element method, namely the fictitious heat source method, is implemented in FRACOD to simulate the temperature change and thermal stresses in rocks. This method is particularly suitable for the thermal-mechanical coupling in FRACOD where the displacement discontinuity method is used for mechanical simulation. An example case is presented where a borehole drilled into the rock formation. Depending on the initial reservoir rock temperature, cooling fractures may or may not occur in the borehole wall from the same differential temperature between the borehole wall and the reservoir rock.