Investigation into the mechanisms of heavy oil recovery by novel alkaline flooding

To investigate the mechanism of alkali flooding for heavy oil recovery, sodium metaborate, which has strong chelating capacity for calcium and magnesium ions, is selected for laboratory research to evaluate its displacement efficiency using sandpacks. The results show that the dynamic interfacial tension between the alkali solution and Xia-8 crude oil is high, and the sandpack tests give evidence of good displacement efficiency, showing that 1.0% NaBO2 can enhance oil recovery by 27.1%. During the displacement process, a large differential pressure response occurs when the alkali concentration is high, and the incremental oil recovery increases with the alkaline concentration. When 0.1% SBET-12 was added to the alkali solution, the interfacial tension was significantly reduced, but the displacement efficiency showed no obvious improvement. 0.1% HPAM was added to the solution to adjust the mobility ratio. However, ternary flooding (NaBO2 + 0.1% SBET-12 + 0.1% HPAM) and binary flooding (NaBO2 + 0.1% HPAM) have the same effect on oil recovery, which shows that the SBET-12 has little effect in improving the recovery of Xia-8 crude oil. The glass etching model test, which is used to further determine the enhanced heavy oil recovery mechanisms of sodium metaborate, shows that the microscopic mechanism involves alkaline solution penetration into the crude oil and the formation of water droplets inside the oil phase, which may act to block the water channel and inhibit the viscous fingering, leading to an improvement of the sweep efficiency.