Pore compressibility in rocks
Pore compressibility in rocks The unjacketed core compressibility in a porous rock is the change in pore volume due to change in pore pressure for constant differential pressure. This parameter affects how the saturated bulk modulus of a rock is related to the drained frame modulus and the pore fluid compressibility. Recent measurements of poroelastic constants and effective medium theories are used to estimate how the pore compressibility depends on effective stress and how uncertainty in the pore compressibility affects uncertainty in Gassmann' equation estimates of the saturated bulk modulus. Results for Berea sandstone and for models of sand-clay mixtures show that the estimate of the change in the saturated bulk modulus due to substitution of different fluids in the rock may differ in size by a factor of two or more if the pore compressibility is approximately equal to the fluid compressibility instead of the grain compressibility. In general, the order of magnitude and sign of the pore compressibility cannot be determined from solid and fluid compressibility information alone.
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