Multiple Flow Mechanism-Based Numerical Model for CO₂ Huff-n-Puff in Shale Gas Reservoirs with Complex Fractures

CO2 huff-n-puff has been proven to be an effectivemethodfor enhanced gas recovery. Besides, considering the storage capacityand existing infrastructure, injecting carbon dioxide into shale gasreservoirs is a feasible geological storage option for carbon dioxide.However, the current huff-n-puff simulation model must consider thecomprehensive flow mechanism crucial for accurate reservoir and huff-n-puffsimulation. Besides, the feasibility of effective CO2 storageby CO2 huff-n-puff in shale gas reservoirs is still beingdetermined. Therefore, a CO2 huff-n-puff numerical modelconsidering gas adsorption/desorption, diffusion, dissolution, stresssensitivity, and stimulated reservoir volume (SRV) is establishedin this paper. The model's reliability is verified by matchingthe production history with commercial software. Finally, the effectsof various flow mechanisms on CO2 huff-n-puff and storagein shale gas reservoirs are analyzed. The results show that CO2 huff-n-puff can significantly improve the gas recovery offractured shale reservoirs and realize the effective storage of partof CO2, where the storage factor can reach 0.62. Consideringadsorption/desorption, diffusion, stress sensitivity, dissolutionin water, and SRV is beneficial to storing CO2 during huff-n-puff.Adsorption/desorption, diffusion, and SRV can enhance the huff-n-puffeffect, while stress sensitivity will weaken. For different mechanisms,adsorption/desorption and SRV can most affect the huff-n-puff andstorage effect in shale reservoirs. This work provides a new approachfor the simulation of CO2 huff-n-puff and storage, whichis beneficial for exploiting the shale gas reservoirs and decreasingCO(2) emissions.