Permeability Evolution of Fractures in Shale in the Presence of Supercritical CO2
By: Sam S. Hashemi, Mark D. Zoback (May 18, 2021)
This article explores the effects of supercritical carbon dioxide (scCO2) on the permeability and surface properties of fractures in diverse shale compositions. Through experimental measurements, the study evaluated how both argon and scCO2, when used as pore fluids, impacted permeability and the displacement of fracture surfaces under varying stresses. The study incorporated both naturally occurring fractures and deliberately saw-cut ones. Following multiple cycles of loading and unloading, a noticeable reduction in permeability and fracture displacement was observed, likely attributed to inelastic compaction. Interestingly, shales with a higher carbonate content revealed an uptick in permeability and evidence of fracture surface deterioration after prolonged exposure to scCO2, suggesting carbonate dissolution as the cause. The research also highlights a clear connection between the responsiveness of permeability to effective normal stress and the associated fracture displacement. Post scCO2 exposure, the fracture surfaces exhibited increased flexibility, leading to a heightened dependence of permeability on the given effective normal stress.