Optimization research and application of pH responsive fluid flow direction agent affecting in-situ generated CO₂ flooding

In order to solve the problem that the effect of multi-round in-situ CO₂ flooding as gradually decreased in Bohai oilfield, the reasons were analyzed through lab physical simulation experiments, and an optimization method for in-situ CO₂ generation technology was proposed by using a pH-responsive plugging. The results of lab experiments showed that the recovery of in-situ CO₂ generation in first round of profile control increased 25.61% on the base of water flooding, the second round had no effect of oil increase. When 0.1PV gel was injected in second round of profile control, the recovery rate increased 6.11% on the basis of first round, but the injection pressure increased rapidly from 0.07 MPa to 0.7 MPa, it was indicated that the gel system could improve oil recovery, but the injectivity was poor. The injection pressure would fluctuate between 0.05 MPa and 0.35 MPa when 0.1PV pH-responsive plugging agent was added in second round of profile control, and the final recovery increased 12.33% on the basis of first round. Displacement pressure did not increase significantly after the adjustment of flooding, which showed that the plugging agent had good injectivity and would not effect the water injection. In 2015 and 2018, two rounds of field tests were conducted in block A of Bohai oilfield. The first round was conventional in-situ CO₂ generation, and the cumulative oil increase was 1 371 m³. In the second round, optimization in-situ CO₂ generation was carried out, then the cumulative oil increase was 2 317 m³, which was significantly better than the first round.