Stress dependence of velocities and permeability in tight gas sandstones

New experimental tests on 18 tight gas sandstone samples from a Saudi Arabia field show a strong dependence of both V_p and V_s on hydrostatic confining stress that varied from practically zero to 50 MPa. The absolute permeability k of the same samples was measured in the same stress range using a gas (nitrogen) permeameter. This Klinkenberg-corrected permeability also showed a dramatic stress dependence. It decreased by one to two orders of magnitude as the stress increased. Combined permeabilityvelocity cross-plots can serve to estimate the permeability from the elastic property variations during time-lapse monitoring, as well as during fracking of these rocks. Theoretical simulations based on the inclusion-based differential effective medium theory confirm the experimental velocity-stress results.