Permeability and rigidity of green river shale before and after interaction with water

We measure acoustic travel-times in Green River shale both parallel and perpendicular to bedding to observe the effects on petrophysical properties of interactions with water (fracture fluids) for different durations. X-ray diffraction shows the samples dominantly comprise carbonate and quartz. Scanning electron microscopy shows morphology of the minerals and pore network of the shale. Horizontal and vertical helium permeability measurements are conducted to analyze permeability evolution under different stress conditions. The samples record very low permeabilities at recreated confining stresses – indicating the need to be stimulated. Permeability decreases with increasing confining stress. Permeability increases with increasing pore pressure due to gas slippage effects. Increasing effective stress generally decreases the permeability. Acoustic travel-time measurements show that compressional and shear wave velocities increase with confining stress. Shear, Young’s and bulk modulus all increase with confining stress with the more rigid samples exhibiting higher fracture conductivity. Compressional and shear wave velocities decrease as the shale is exposed to water and quartz dissolves from the pore structure, reducing moduli and acoustic velocities of the samples that exhibit lower fracture conductivity. Measured porosities suggest greater accessibility of the pores from a direction parallel to bedding.