Porosity and Permeability Change under Stress and Correlation to Rock Texture

Abstract

Laboratory experiments and numerical simulations were used to study the effect of pore structure on stress-porosity-permeability relations. It has been hypothesized that heterogeneous multi-porosity system with the permeability-controlling porosity more compressible than the other porosities would demonstrate a high stress-sensitivity in the permeability. The porosity and permeability of carbonate, sandstone, and fractured cores were measured under isostatic stress conditions. A power law was used to correlate the change in permeability to the change in porosity. While the power-law exponents for the sandstones were similar to that expected from a Kozeny-type correlation, carbonate and fractured cores showed much higher stress-sensitivity. The pore structure of a tested carbonate, examined by X-ray computed tomography, showed strong heterogeneity. Numerical simulation of porosity and permeability reduction during a uniaxial compression of an artificial vuggy porous medium, using discrete-element and lattice-Boltzmann methods, directly confirmed the influence of the pore structure on the stress-sensitivity.

DEM-LBM simulation of stress-dependent absolute and relative permeabilities in porous media

“…This agreement indicates that stress sensitivity of porosity and absolute permeability of our medium is mostly similar to those of an idealized capillary tube bundle and the tight sandstones previously studied. [19,20]. Pore throats or fractures that control the overall permeabilities of cores only contribute to a small fraction of the net porosity.…”

“…Experimental results showed that + in fractured rocks are higher than those in carbonates, which in turn are higher than those in sandstones [20]. It was pointed out that pore throats are more stress sensitive than pore bodies, which would lead to larger values of + [21].…”

“…It was pointed out that pore throats are more stress sensitive than pore bodies, which would lead to larger values of + [21]. Similarly, as conductive fractures are more stress sensitive than pores in rock's matrix, fractured rocks also exhibit larger values of + [20].…”

“…Particle-particle interaction model parameters for DEM and porous medium bulk mechanical properties[20].…”