LLNL gas-stimulation program. Semiannual progress report, October 1980-March 1981

Preliminary theoretical and experimental analyses of fracture propagation in a nonuniform stress field have been performed. Results indicate fracture propagation is strongly influenced by existing stresses. A stress gradient in the existing stress field results in either the fracture stopping or, when over-driven, turning and propagating normal to the minimum stress. We have completed some preliminary analyses of fluid flow in apertures, and also characterized the mechanical properties of some of the core material from Mesaverde sandstones and shales from wells in Wyoming and Colorado. Our studies have continued to determine the feasibility of ultrasonic techniques in measuring in-situ stresses. Our effort has been directed toward developing a transducer package to test the measurements in a borehole, however, we have also concentrated on techniques to evaluate and interpret measurements. The effect of stress on velocity anisotropy has been shown in the laboratory, but the measurements are complicated by dynamic mode contamination. In our geologic studies we have continued to relate in-situ stresses to geologic structure, examining the effects of pore pressure increases on fracturing in the Green River Basin due to gas generation.