Experimental research on the optimization and evaluation of the polymer/Cr³⁺ deep profile control system for heterogeneous fractured low-permeability reservoirs

There are strong heterogeneities in fractured low-permeability reservoirs, and the fracture network leads to a sharp increase of the water cut in production wells, which causes a rapid decline in production, and overall poor recovery efficiency. This article focuses on the effects of fractures on water cut in reservoir developments for Chaoyang Gou Oilfield of China, the formula of the profile control system of the polymer/Cr³⁺ has been determined by taking the conducting indoor profile control experiments, and the injectability, sealing ability, compatibility of formation water, thermal stability, and shear resistance of the profile control system are evaluated by taking the long core experiments. Then, the reasonable formulas for different matrix/fracture permeability levels’ combinations are determined through the profile control system oil displacement experiments and the field test effects are evaluated. The results show that a series of profile control systems suitable for heterogeneous fractured low-permeability reservoirs are optimized. For the 15 × 10⁻³μm² permeability level, the concentration of 13 million molecular weight polymer is recommended to be more than 1500 mg/L, and the 16 million molecular weight with 1000 mg/L for the 30 × 10⁻³μm2 level, the 19 million molecular weight with 500 ∼ 1000 mg/L for the 45 × 10⁻³μm² level. The application effect in oil fields shows that the water cut decreased by 8.65% points, and the cumulative oil increase is 1601t after profile control. The research results provide an effective formula for improving the oil recovery in low-permeability reservoirs.