Anisotropic Permeability Influencing the Performance of Free CH₄ and Free CO₂ during the Process of CO₂ Sequestration and Enhanced Gas Recovery (CS-EGR) from Shale

Abstract

To explore how anisotropic permeability affects the performance of free gases (CO 2 and CH 4 ) during the process of sequestrate CO 2 and enhance gas recovery (CS-EGR) in shale reservoirs, this work develops an integrated thermo-hydromechanical (THM) coupling model, where the anisotropic parameter k (k = k h /k v ) is embedded, where k v and k h represent the permeability in the vertical and horizontal directions, respectively. Results indicate that anisotropic permeability has a significant influence on the free gas density, the porosity of shale matrix or fracture, and the content of free gas. A higher k usually enables more free CO 2 to be accumulated in the shale matrix/ fracture and more free CH 4 to be recovered from production wells. Besides, k variation also significantly affects the distribution of free gases, and more free gases tend to migrate along the direction that has a greater permeability. Depending on two self-defined parameters, a higher k makes more adsorbed CH 4 be desorbed and thus is more appropriate for the CH 4 recovery via CS-EGR operation, while ∼65% injected CO 2 is trapped as the adsorbed phase in shale reservoirs under variable k values. Hopefully, the fresh approach in this work will be helpful for deepening knowledge on the CS-EGR behavior in shale.

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