Stress and Pore Pressure Distribution Around a Pressurized, Cooled Crack in Low Permeability Rock

Abstract

Thermoelastic and poroelastic stresses associated with water injection and hydraulic fracture stimulation can result in rock failure in the vicinity of the main fracture leading to permeability change and enhanced micro-seismicity. The monitoring and analysis of the micro-seismicity is used to better understand stimulation outcomes, and this process can benefit from a stress/failure analysis. A coupled displacement discontinuity method is used in this paper to study the stress and pore pressure changes around a cooled fracture in low-permeability rock, to investigate their contribution to rock failure and seismicity. Simulations of a uniformly cooled crack indicate that cooling introduces a transient reduction in pore pressure that has a stabilizing effect with respect to shear failure of intact rock and slip on pre-existing cracks. Thermally-induced stresses also cause formation of new secondary cracks that can generate micro-seismic events. Regions of enhanced shear stress with higher potential for shear failure are also observed near the crack ends and off the main fracture plane. The distribution of the stress and pore pressure fields vary with time, resulting in a time-dependent rock failure distribution.