Pilot test on CO₂ flooding of Chang 4+5¹ oil reservoir in Yougou region of the Ordos Basin

In the Ordos Basin, there are abundant reserves in low-permeability oil reservoirs, but their water flooding effects are not satisfactory. In addition, the water resources in northern Shaanxi are deficient. Therefore, it is in urgent need to develop a new flooding technology for cost reducing and efficiency increasing. In view of the characteristics of Chang 4+5¹ oil reservoir in Yougou oil region of Wuqi Oilfield, the simulation experiment of CO₂ flooding was conducted by using the slim tube of 20 m at the temperature of 60 ℃. Then, the construction parameters were designed based on the characteristics of the oil reservoir, and 5 well groups were selected for the CO₂ flooding pilot. Finally, the field construction situations were analyzed from the aspects of formation pressure comparison before and after CO₂ injection, CO₂ flooding effect and CO₂ leakage monitoring in the construction area. It is indicated that Chang 4+5¹ oil reservoir satisfies the conditions of CO₂ miscible flooding and the wellhead pressure of 8 MPa and the flow rate of 0.6 t/h can guarantee its miscible phase. CO₂ advances uniformly in the reservoirs and the formation pressure recovers steadily. The oil increment of two years’ CO₂ miscible flooding is 2 935.6 t higher than that of water flooding in the same period, its CO₂ to oil exchange ratio is 3.03∶1, and no CO₂ leakage is detected in the soil of the test region. The research results can provide the technical support for the safe popularization of carbon capture, utilization and sequestration (CCUS) technology in the Ordos Basin, and the technical reference for the stable production of Yanchang Oilfield and the sustainable development of local economy in northern Shaanxi.