Study on EOR method in offshore oilfield: Combination of polymer microspheres flooding and nitrogen foam flooding

Abstract Nitrogen foam flooding and polymer microsphere flooding have been applied for improving the developmental effect of the high water-cut period in offshore oilfields in recent years. The combination of polymer microsphere flooding and nitrogen foam flooding as a novel technology for enhanced oil recovery was developed in offshore oilfields, due to their injectability, propagation and in-depth plugging property. The goal of the current research was to evaluate the performance of polymer microspheres, screen the appropriate nitrogen foam system, determine the displacement effect of the combination technology by performance measurements and displacement experiments in a laboratory, then the mechanism of profile control and oil displacement was concluded. The experimental results indicated that the polymer microspheres were suitable to inject into the formation due to their swelling and plugging abilities, and the plugging rate of polymer microspheres could reach 96% at 2000 mg/L. The foam system was composed of a 5000 mg/L foaming agent, S2, and a 1000 mg/L stabilizer, P1, the optimal gas-liquid ratio was 1:1, and the best foam slug combination was alternating injections with multiple slugs. In addition, the oil recovery increment of the combined technology (24.65%) was larger than those of the microsphere flooding (12.35%) and foam flooding (18.3%) alone, especially for the low permeability layer. According to the laboratory results, a pilot test was conducted at well group W1 in the Bohai A oilfield, and the test showed that the combined technology can attain the oil increment of 64461 bbls. Therefore, the combination of polymer microsphere flooding and nitrogen foam flooding can help to enhanced the oil recovery more efficiently.