Heterogeneous Transport of Free CH4 and Free CO2 in Dual-Porosity Media Controlled by Anisotropic In Situ Stress during Shale Gas Production by CO2 Flooding: Implications for CO2 Geological Storage and Utilization

High Resolution Image Download MS PowerPoint Slide 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.