CO₂-EOR numerical simulation in cores from the Third Member of the Funing Formation in Zhangjiaduo oilfield, Subei Basin

CO2-enhanced oil recovery (CO2-EOR) is currently one of the most widely applied technologies worldwide for oilfield production stimulation and carbon sequestration. Under the "dual carbon" goals, numerical simulation of CO2-EOR needs to consider the effect of interphase mass transfer by the non-independent water phase, so as to characterize the multiphase dissolution distribution of CO2. Objective and MethodsBased on actual reservoir conditions of the Third Member of the Funing Formation in Zhangjiaduo Oilfield, Subei Basin, this study used the multiphase flow numerical simulation software TOGA to establish a core displacement model, and realized the simulation of three-phase full-component miscibility. By simulating the interactions between CO2 and reservoir fluids under different confining pressures and gas injection rates, the differences in CO2 solubility in the water, gas, and oil phases under the actual reservoir conditions of the study area were characterized, revealing the miscible flooding mechanism. ResultsThe simulation results indicated that the minimum miscible pressure for miscible flooding in the study area was 30 MPa, at which the oil-gas interfacial tension approached zero. Miscible displacement significantly improved oil recovery, with recovery rates of 85% and 52% under confining pressures of 38 MPa and 10 MPa, respectively. CO2 solubility in the oil phase was much greater than in the water phase, and with increasing confining pressure, the mole fractions of CO2 in both oil and water phases increased. At confining pressures of 22 MPa and 38 MPa, the mole fractions of CO2 migrating in the water phase were 1.8% and 2.1%, respectively, while those in the oil phase were 70% and 80%, respectively. The reservoir conditions in the study area can achieve miscible flooding, which is also conducive to carbon storage. Increasing the gas injection rate can improve production efficiency, but has a little effect on the ultimate oil recovery and CO2 sequestration capacity, while potentially increasing the risk of gas channeling. ConclusionThis study provides technical references for field simulation and leakage risk assessment of the Third Member of the Funing Formation in Zhangjiaduo oilfield.