Composite Plug-Removal Technology for Polymer Profile Control Wells in Sandstone Reservoirs

To address the problems of high injection pressure, unclear plugging mechanisms, and poor performance of conventional stimulation and plugging-removal measures in polymer-containing profile-control wells of the Sha-3 reservoir in the Liuzan North Block, the plugging mechanism was investigated by X-ray diffraction, scanning electron microscopy (SEM), and core flooding experiments. The results show that the plugging materials are composite plugging materials formed by the interaction of retained profile-control polymers in the reservoir with heavy components and clay minerals. These plugging materials are characterized by stable structures and complex compositions. Based on the characteristics of the plugging materials, a composite plug-removal agent system was optimized, and the corresponding treatment parameters were determined. The optimized plugging-removal system was composed of 0.5 wt % surfactant as an oil-washing agent, mud acid (12 wt % HCl + 2 wt % HF) as an inorganic dissolution agent, and 5 wt % JD-Y as a polymer degradation agent. This system exhibited high dissolution efficiency for different types of plugging components. After the addition of functional additives, including 1.0 wt % HS-3 corrosion inhibitor, 1.5 wt % EG-13 iron ion stabilizer, and 2.0 wt % LA5 clay stabilizer, the corrosion rate of the acid system decreased to 3.16 g·m^-2 ·h^-1, effectively reducing corrosion of metal equipment. The antiswelling rate reached 82.01%, and the iron-stabilizing capacity was 207.89 mg/mL, indicating excellent antiswelling performance and iron-stabilizing ability. When the composite plug-removal agent system was injected at the optimal dosage ratio of 1:1:3 and reacted at 90 °C for 4 h, both the degradation rate and permeability recovery exceeded 80%, and the core permeability increased by approximately 13 times. The proposed composite plug-removal agent system can effectively dissolve complex plugging materials formed during polymer flooding and provides a technical reference for plugging removal in sandstone reservoirs.