Mechanistic Insights and Parameter Sensitivity of Advanced CO2 Injection in Tight Oil Reservoirs

Abstract In the process of CO2 injection development in tight oil reservoirs, there are some problems such as early gas breakthrough and insufficient utilization of remaining oil in nanopores, which restrict the effect of CO2 enhanced oil recovery. Advanced CO2 injection is a novel gas injection method with the potential to both replenish formation energy and control gas channeling. However, its production enhancement mechanism and the optimization of key parameters in tight oil reservoirs remain unclear. In this study, tight oil reservoirs in the Ordos Basin were selected as the target reservoirs. Slim-tube experiments, core flooding tests, T2 spectrum analysis, and core-scale numerical simulation were combined to systematically evaluate the miscibility conditions, development performance, and key parameters of advanced CO2 injection. The results show that the minimum miscibility pressure (MMP) is 21.54 MPa, indicating that it is generally in the near-miscible state under the original formation conditions. Compared with continuous CO2 injection, advanced CO2 injection delayed the gas breakthrough time from 0.78 to 0.84 PV, and the recovery increased from 74.09 to 80.05%. Among them, the utilization degree of crude oil in 0–0.1 μm increased from 12.46 to 22.06%, and its contribution rate to total recovery increased from 18.53 to 26.24%, revealing the pore-scale characteristics of the advantage of advanced CO2 injection to increase recovery. Furthermore, a three-dimensional heterogeneous numerical model was established at the core scale. The matching rate between the simulation results and laboratory core flooding results under different permeability conditions exceeded 95%. This verifies the reliability of the model for parameter optimization of advanced CO2 injection. On this basis, sensitivity analyses of advanced injection volume and shut-in time were carried out. Both parameters had significant effects on development performance. Considering recovery factor, breakthrough time, and time cost, the optimal advanced injection volume and shut-in time were determined to be 0.15 PV and 12 h, respectively. The results of this study can provide a basis for the optimization of development parameters and field implementation of advanced CO2 injection in tight reservoirs.