Experimental Study on Rock Deformation and Permeability Variation
The development of a petroleum reservoir would inevitably induce a rearrangement of the in-situ stress field. The rearrangement of the stress field would then bring about a deformation of the reservoir rock and a change of the permeability. This experimental study was carried out to investigate rock deformation and its impact on axial permeability. Triaxial compression tests were conducted on Berea sandstone, Indiana limestone, Westerly granite and tuff specimens. Axial permeability was continuously measured for Berea sandstone and Indiana limestone during triaxial compression tests. The axial permeability of fractured Westerly granite specimens was also measured during hydrostatic compression tests. Acoustic emission (AE) monitoring was performed to help improve the understanding of rock deformation. Results showed that Berea sandstone and Westerly granite were relatively brittle, while Indiana limestone and tuff were relatively ductile. Rock deformation altered pore structures and the change of pore structures considerably impacted fluid flow through rock. For porous Berea sandstone and Indiana limestone, the destruction of the pore structure by rock deformation led to a decrease in axial permeability. For tight Westerly granite, fractures created by rock deformation significantly improved the ease of fluid flow. Acoustic emission response was found to be strongly dependent on rock type. Brittle Berea sandstone and Westerly granite produced high AE rates during compression tests, while ductile Indiana limestone and tuff generated very low AE rates.