Development and Performance Evaluation of a High-Temperature-Resistant Self-Healing Composite Gel Plugging Agent Modified With Curdlan in Shale Gas Operations

Summary

Lost circulation is a common and complex challenge in deep shale gas drilling operations, while the insufficient thermal stability of conventional self-healing gel plugging agents limits their application at elevated temperatures. In this work, curdlan was introduced into a hydrophobically associating stearyl methacrylate-acrylamide-acrylic acid (SMA-AM-AA) polymer to develop a high-temperature-resistant self-healing gel plugging agent, denoted as SAC (S for stearyl methacrylate, A for acrylamide and acrylic acid, and C for curdlan). The effects of curdlan content on self-healing time, swelling behavior, mechanical and rheological properties, and plugging performance were systematically evaluated. Increasing the curdlan content enhanced the mechanical and rheological properties of the gels but prolonged their self-healing time, indicating a trade-off between self-healing efficiency and mechanical strength. At 120°C, SAC-3 required the longest mean self-healing time (8.2 ± 0.3 hours), but among the formulations self-healed at this temperature, it exhibited the highest storage modulus (3,619 Pa), elastic modulus (3.47 ± 0.18 kPa), and toughness (30.9 ± 2.3 kJ/m3), providing the most favorable overall balance. After aging at 120°C for 16 hours, SAC-3 alone showed a mean pressure-bearing capacity of 6.2 ± 0.4 MPa, with a maximum value of 6.5 MPa. The SAC-3/walnut-shell composite formulation further increased the pressure-bearing capacity to 14.5 ± 0.9 MPa, with a maximum value of 15.2 MPa. These results are consistent with reinforcement of the gel network through multiple reversible physical interactions, which may facilitate the formation of a more stable plugging layer at elevated temperatures.