Permeability Evolution of Fractures in Shale in the Presence of Supercritical CO2

• Published in: Journal of geophysical research. Solid earth 2021-08, Vol.126 (8), p.n/a
• Main Authors: Hashemi, Sam S., Zoback, Mark D.
• Format: Article
• Language: English
• Subjects: aperture; Argon; Carbon dioxide; Carbonates; Compaction; Composition; Cycles; Degradation; Displacement; Dissolution; Dissolving; Exposure; Fluids; Fracture permeability; fracture roughness; Fracture surfaces; Geophysics; Laboratory experiments; Normal stress; Permeability; Sedimentary rocks; Sensitivity; Shale; Shale rocks; Shales; supercritical CO2; Surface properties; Unloading
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2021JB022266

We experimentally examined the impact of supercritical carbon dioxide (scCO2) on fracture permeability and fracture surface characteristics in shales of various compositions. We measured permeability and fracture normal displacement at different effective stresses using both argon and scCO2 as pore fluids. Both natural fractures and saw cuts in intact samples were used in our study. The permeability and fracture normal displacement decrease after multiple loading/unloading cycles, apparently as the result of inelastic compaction. In samples with high carbonate content, we observe an increase in permeability and fracture surface degradation after more than 3.5 days of exposure to scCO2, apparently due to carbonate dissolution. We demonstrate that the sensitivity of permeability to effective normal stress correlates well with the fracture normal displacement. The dependence of permeability on effective normal stress increases after exposure to scCO2 as the fracture surface became more compliant. Plain Language Summary In this study, laboratory experiments were used to investigate the effect of supercritical carbon dioxide (scCO2) on the fracture permeability and fracture surface characteristics of shales. Supercritical state is characterized by the inability to distinguish whether CO2 is a liquid or a gas. For samples with a wide range of compositions, we measured permeability and fracture normal displacement at different stresses using both argon and scCO2 as pore fluids. Both natural fractures and saw cuts in intact samples were used. The fracture normal displacement and permeability decrease after multiple loading/unloading cycles, apparently as the result of irreversible compaction. In samples with high carbonate contents, we observe an increase in permeability and fracture surface degradation after more than 3.5 days of exposure to scCO2, apparently due to carbonate dissolution. We demonstrate that the sensitivity of permeability to net pressure normal to the fracture surface correlates well with the fracture normal displacement. The sensitivity of permeability on net pressure normal to the fracture surface increases after exposure to scCO2 as the fracture surface became more compliant. Key Points We studied the effect of scCO2 on fracture permeability evolution and fracture surface characteristics in shales Carbonate dissolution and inelastic compaction appear to mitigate each other's impact in controlling permeability Time‐dependency of the carbonate