Performance and evaluation on stress-dependent permeability and flow characteristics for CO2-enhanced oil recovery in fractured shale

Scholars are investigating the viability of enhancing shale oil recovery and geological CO2 storage. However, the multi-phase flow and stress sensitivity of fractures intensify the complexity of fractured shale. A semi-analytical model of three-phase flow considering stress-dependent permeability (SDP), desorption, and CO2 huff-n-puff is proposed. A three-region model, comprising a primary fracture region, an enhanced fractured region, and a non-stimulated region, is employed to characterize the zoning of fractured wells. The three-phase distance of investigation is derived to characterize the dynamic drainage of formation fluid. Different stress sensitivity indexes are employed to characterize the SDPs in each region, and Langmuir's theory is used to model the effect of desorption. Then, the inter-region flow rates are provided analytically. Finally, a successive iteration is used to update the dynamic parameters by coupling the material balance equations (MBEs). The production curves exhibit good agreement with the fully numerical result while requiring less computational time (15 min to 3 s). The saturation of PFR influences the gas production within 30 days, and the range of EFR will significantly influence gas production within 500 days. The SDP in fractures and matrix will reduce reservoir production significantly (about 50%). The desorption in matrix will improve the production of gas throughout production. The effects of CO2 huff-n-puff are evaluated by simplifying the effects of CO2 as the change of pressure and pressure–volume–temperature data of the fluid. The production increases significantly (about 22%) when the CO2 content exceeds 20%.