Effective Gas Permeability Measurements at Different Water Saturations in Tight Sandstones-Differentiation between Slip Flow and Capillary Controlled Flow Regimes

摘要

Gas permeability experiments were performed on partially and fully water-saturated tight gas sandstone samples. The tests were conducted at confining pressures of 15, 20, and 30 MPa and at different mean gas (He, N_2) pressures up to 6 MPa in order to account for the slip-flow effect. With increasing water content gas permeability coefficients decreased by up to three orders of magnitude. Furthermore, in the plot of apparent permeability vs. reciprocal mean pressure the usually observed "Klinkenberg trend" was found to become non-linear and exhibited negative intercepts with increasing water saturation and differential pressure. This can either be due to capillary pressure-controlled water drainage or dilatation of the pore network. Effective gas permeability is therefore not simply controlled by the absolute water-content of the pore system but additionally by the effective and differential pressure. This may have important implications for gas productivity, as water content and fluid pressure and effective stress change dynamically during dry and wet gas production.