Poroelastic Parameters of Sandstone Under Various Combinations of Pore Pressure and Confining Pressure

A long-term monitoring of carbon dioxide (CO2) in a reservoir at depth is required for the geological storage of CO2. For this requirement, an inversion technique utilizing tilt data of the ground surface associated with migration of CO2 may be one of promising techniques. Since the inversion technique is based on the poroelastic theory, poroelastic parameters of reservoir rocks (e.g., sandstone) should be well understood to increase reliability of the monitoring technique. Understanding of poroelastic parameters is also essential in a geomechanical model simulation of the geological sequestration of CO2. For this purpose, focusing on a water-saturated part within a sandstone reservoir, a set of five kinds of laboratory tests were conducted on Kimachi sandstone saturated with water, to determine poroelastic parameters at various combinations of confining pressure (7–40 MPa) and pore pressure (5–25 MPa), namely various Terzaghi's effective stresses (2–35 MPa). Skempton's coefficient B and undrained bulk modulus were determined by B-test, in which volumetric strain and pore pressure changes with confining pressure. Drained bulk modulus and poroelastic parameter H (inverse number of poroelastic expansion coefficient) were determined by P-test and H-test, in which volumetric strain changes with confining pressure and pore pressure, respectively. Young's modulus and Poisson's ratio were determined by both drained and undrained triaxial compression tests. Confining pressure and pore pressure dependencies for the poroelastic parameters were evaluated separately, revealing that both dependencies may be integrated by Terzaghi's effective stress dependency.