Linear pressurization method for determining hydraulic permeability and specific storage of a rock sample

We studied the methodology and applicability of linear pressurization for determining simultaneously hydraulic permeability and specific storage of a rock sample. We analytically solved the governing equation for 1-D pressure diffusion through a homogenous, isotropic cylindrical rock specimen located between a downstream and an upstream reservoir considering linear pressurization of the upstream fluid as the boundary condition. The solution consists of a transient and a steady state for which both differential pressure between the two reservoirs and injection rate at the upstream reservoir assume constant values. Since the steady-state differential pressure is linearly proportional to the compressive storage of the downstream reservoir, tests conducted with a systematic variation of the size of the downstream reservoir permit determining permeability and specific storage from the intercept and slope of the linear relationship. Alternatively, simultaneous measurement of differential pressure and fluid injection rate at steady-state conditions provides a basis for calculation of the hydraulic properties as previously presented for linear injection. Experiments were performed on Fontainebleau sandstone samples to document the feasibility of the method. The determined storage capacity value is used to calculate various poroelastic parameters, such as bulk and pore-space compressibility, Skempton and the effective pressure coefficient.