A strain based approach to calculate disparities in pore structure between shale basins during permeability evolution

We test the permeability response of Marcellus shale and Wolfcamp shale under changing strain. While magnitude of strain for a given stress is determined predominantly through mineral composition, the response of transport properties to a given strain are dependent on pore density, pore geometry, and rock fabric/mineral distribution around pores. We characterize the differences between the two shales using bulk mineralogy, SEM imaging with elemental analysis, and the cubic law for permeability evolution. We find that the Marcellus shale is comprised predominantly of clays that leads to more deformation when stressed than the Wolfcamp shale which is composed predominantly of quartz and calcite. The level of creep and compaction are directly related to the amount of clay in each shale sample. A novel result of our study is a strain-driven model to capture permeability evolution in shale due to differences in pore structure.