Combined flooding systems with polymer microspheres and nonionic surfactant for enhanced water sweep and oil displacement efficiency in heterogeneous reservoirs

A new microspheres-surfactant flooding system consisting of polymer microspheres and nonionic surfactant has been detailed to enhance oil recovery of Bohai oilfield by increasing the sweep efficiency of water and the oil displacement efficiency of surfactant synchronously. The surface morphology and particle size distribution of polymer microspheres have been investigated through scanning electron microscopy and dynamic lighting scattering. In addition, plugging performance, oil displacement efficiency and the deep profile control process of combination system have been studied by utilizing assembled parallel double cores models and core displacement experiments. The experimental results have shown that the initial appearance of the polymer microspheres was regularly spherical; the particle size distribution was from 200 nm to 6 μm. The particle size of the microspheres after swelling was increased by nearly five times compared with the original particle size. The combination system could exhibit an effective injectivity and plugging effect for cores with different permeability from 0.5 μm2 to 3.0 μm2. This system could significantly reduce fractional flow through high permeability channel, and also present good profile control effect and oil displacement efficiency in parallel double cores. By the injection of the 2.5 PV microspheres solution, the microspheres flooding recovery could improve about 34% more than water flooding. The slug composition, with 400 mg/L polymeric microspheres and 0.3% nonionic surfactant, could obtain a higher oil recovery by 4 wt% original oil than the microspheres system. The combination system could be recommended as a potential combination for profile control in Bohai heterogeneous reservoirs.