Abstract
The poroelastic effect addresses the coupled deformations of the solid framework and the fluids in a porous rock. It also studies the effective stresses that result from this coupled behavior. Because fluids can move through the porous medium, at a rate controlled by their permeability, local increases in pore pressure, resulting from local pore strains, dissipate as a function of time. This behavior makes the poro-elastic effect time-dependent, and is long-lasting for low permeability rocks. For some applications (e.g., borehole stability in low permeability rocks), evaluating the transient effect is critical to anticipating and preventing failure. For other applications (e.g., evaluating the in-situ effective stress), the equilibrated steady-state condition is needed. The Biot and Skempton coefficients are the two fundamental rock properties that are needed to understand the poro-elastic effect. In this paper, we discuss a methodology for evaluating the Biot’s coefficient and to evaluate its variability along the directions parallel and perpendicular to bedding. We also discuss implications of the poroelastic effect for applications to oil and gas producing tight shale reservoirs. The effects are illustrated by examples, using data from laboratory tests. Most importantly, we provide values of Biot’s coefficients that could be used for applications in organic-rich mudstone reservoirs.