International Journal of Rock Mechanics and Mining Science, October 1988
Authors: M. P. Hardy and M. I. Asgian (AAI)
This paper addresses the problem of the interaction of borehole and fracture fluid pressures on fracture reopening during pressurization cycles used to determine the maximum principal stress perpendicular to a borehole in impermeable rock. Our interest arose because of discussions on the interpretation of “hydraulic fracture” test results conducted at the Hanford Site, Richland, Washington. For these tests, the maximum principal stress was determined from the secondary breakdown pressure. Recognizing the pressure in the fracture is coupled to the borehole pressure and depends on the fracture aperture, the rate of pressurization, fluid properties, and the deformability of the fracture, a simple equation, such as this equation, is a crude approximation for a complex process. Recently, Asgian (1988) completed a study of fluid flow in deformable, naturally fractured reservoirs and during that study developed a computer code, FFFLOW, to analyze coupled fluid flow/joint deformation problems. We have applied that code to the fluid flow-fracture reopening problem associated with interpretation of hydraulic fracturing stress determinations. After defining the problem and presenting the results of a numerical study, the implications for interpretation of hydraulic fracturing tests for stress determination are discussed. Changes in operating procedures are suggested to improve the interpretation of the fracture reopening tests.
