Composite Injection of Polymer Gel and Polymer Particles for Plugging High-Permeability Reservoir Channels and Improving Oil Recovery

In situ cross-linked polymer gels (ISCPG) and polymer particles are important conformance control agents for water control and oil recovery in oilfields. However, single ISCPG or polymer particle in had problems of incomplete plugging in high-permeability channels and difficulty in achieving effective flow diversion. This study proposed the composite use of three types of polymer particles and ISCPG. Displacement experiments were carried out using a high-permeability model and a fracture-parallel model to evaluate the injection and plugging performance of both single and composite gel systems. Based on these results, the optimal particles for plugging were selected, and then the mechanism of synergistic enhancement was analyzed. Moreover, the injection sequence and slug size were optimized to enhance plugging efficiency and improve oil recovery. Results showed that flexible particles (FP) had good elastic deformation capability and structural strength, and their plugging effect was superior to preformed particle gels (PPG) and adhesive particles (AP). When the “particles-first, gel-later” injection method was applied in a high-permeability sandpack, and FP and ISCPG were blended at a ratio of 8:2, the synergistic plugging performance was optimal. In addition, in the fracture model, when the FP-to-ISCPG ratios were 10:0, 9:1, 5:5, and 0:10, the oil recovery factors of the systems were low, all below 6%. At FP-to-ISCPG ratios of 8:2 and 7:3, the oil recovery factors were 82% and 40%, respectively. These results indicated that the composite gel system with an FP-to-ISCPG ratio of 8:2 achieved the best synergistic effect, resulting in the highest oil displacement efficiency. The composite gel system of ISCPG-FP improved plugging strength and conformance efficiency through the synergy of initial elastic deformation bridging by FP, followed by subsequent filling with ISCPG.