Preparation, Evaluation and Field Application of Thermally Induced Crosslinked Polymer Gel Leakage Plugging Agent

Addressing the complex issue of lost circulation in drilling operations is crucial as it increases nonproductive time and costs. Conventional gel plugging materials often exhibit low temperature resistance, poor pumpability, and low pressure-bearing capacity. To overcome the limitations, a self-made polymer (HSA) was initially synthesized and mixed with two crosslinker agents (MBA/PEI) at room temperature to induce a new type of high-temperature-resistant and pressure-resistant polymer gel agent (HSA-G). Investigating the gel strength and plugging capacity, the vertical inverted tube observation, 71-type high-temperature and high-pressure (HTHP) instruments, and high-pressure filter with varying fracture cracks (3–5 mm) were employed. HSA-G demonstrated excellent gelation strength for 4–5 h at 140 °C, while retaining more than 57% of its gel strength after aging at 140 °C for 144 h, which is 3 times higher than the commercially available hydrolyzed polyacrylamide (HPAM + PEI). The excellent performance was attributed to the synergy between PEI-MBA, which induces tight-crosslinked interconnected structure within HSA-G, mitigating fluid losses to only 72 mL compared to 194 mL for HPAM-G, under 8.5 MPa in the HTHP sand bed at 140 °C. In the fracture leakage simulations using a 5 mm crack performed at 6 MPa at room temperature, the filtration loss of HSA-G is 300 mL, almost half that of HPAM-G, showcasing its superior plugging and high-pressure bearing performance. In conclusion, HSA-G has not only demonstrated operational effectiveness in reducing downtime costs and fluid losses but can also temporally replace cement plugging to prevent reservoir contamination in alignment with environmentally friendly practices.