Experimental determination of poroelastic constants for sandstone under geologic CO_2 sequestration conditions

摘要

A long-term monitoring of carbon dioxide (CO_2) in a reservoir at depth is required for therngeological storage of CO_2. For this requirement, an inversion technique utilizing tilt data of thernground surface associated with migration of CO_2 may be one of promising techniques. Since therninversion technique is based on the poroelastic theory, poroelastic constants of reservoir rocks (e.g.,rnsandstone) should be well understood to increase reliability of the monitoring technique.rnUnderstanding of poroelastic constants is also essential in a geomechanical model simulation of therngeological sequestration of CO_2. For this purpose, focusing on a water-saturated part within arnsandstone reservoir, a set of five kinds of laboratory tests were conducted on Kimachi sandstonernsaturated with water, to determine poroelastic constants at various combinations of confining pressurern(7-40 Mpa) and pore pressure (5-25 Mpa), namely various Terzaghi’s effective stresses (2-35 Mpa).rnSkempton’s coefficient B and undrained bulk modulus were determined by B-test, in whichrnvolumetric strain and pore pressure changes with confining pressure. Drained bulk modulus andrnporoelastic constant H (inverse number of poroelastic expansion coefficient) were determined byrnP-test and H-test, in which volumetric strain changes with confining pressure and pore pressure,rnrespectively. Young’s modulus and Poisson’s ratio were determined by both drained and undrainedrntriaxial compression tests. Confining pressure and pore pressure dependencies for the poroelasticrnconstants were evaluated separately, revealing that both dependencies may be integrated byrnTerzaghi’s effective stress dependency. That is, every poroealstic constant (y) may be described by arnfunction of Terzaghi’s effective stress (σ_(εff)), y=a+b(1-e~(-σ_(eff)/10)), where a and b are constants.