Heterogeneous Transport of Free CH(4) and Free CO(2) in Dual-Porosity Media Controlled by Anisotropic In Situ Stress during Shale Gas Production by CO(2) Flooding: Implications for CO(2) Geological Storage and Utilization

[Image: see text] Regarding shale gas production by CO(2) flooding, few existing reports explain the performance of free CH(4) and free CO(2) in shale reservoirs controlled by anisotropic in situ stress, partly restricting the integrated recognition of shale-based CO(2) geological storage and utilization (CGSU). In this work, a self-developed model embedded with thermo-hydro-mechanical coupling relationships is introduced to investigate how the anisotropic in situ stress determines the transport of free gases (CH(4) and CO(2)) after CO(2) is injected into the shale. Therefore, the stronger anisotropy of in situ stress enables more CO(2) in the free phase to be trapped in the shale reservoir and is insignificant for the content of residual free CH(4) compared to the situation under isotropic in situ stress. Along with CO(2) injection into the shale, the matrix porosity decreases invariably, while the fracture porosity decreases first and then increases gradually. Therein, the variation amplitude of the matrix/fracture porosity is more distinct under a stronger anisotropic in situ stress. The simulations also suggest that the ratio of free CO(2) relative to all free gases in shale is ∼65% at most after sufficient CGSU operation. Hopefully, this comprehensive work is helpful in enhancing the knowledge on the promising shale-based low-carbon CGSU technique.