Mark D. Zoback

Identification Of Hydraulically Conductive Fractures From The Analysis Of Localized Stress Perturbations And Thermal Anomalies

A number of key questions need to be addressed before the relationship between stress and fluid flow in the Earths crust can be understood. First, how is fluid flow related to the current stress field in highly fractured crystalline rock? Second, is enhanced permeability and permeability anisotropy principally the result of flow along joints (Mode I failure) or shear faults (Mode II failure) or both? Is it possible that answer is neither - that in highly fractured crystalline rock, flow is dominated by the orientation of faults and fractures introduced into the rock mass during its long geologic history and the orientation of these structures bears no strong relation to the current stress field? It is well known that relatively few fractures in fractured rock serve to conduct fluids through the rock. The use of fracture geometry to predict hydrologic flow in the crust is therefore severely limited by the lack of knowledge of which fractures measured in a given survey actually provide conduits for fluid flow. This study examines the relationship between in situ stress and fluid flow using data from detailed analyses of wellbore breakouts and fracture geometry in conjunction with precision temperature logs.