Shape Memory Polymers as Smart Lost Circulation Materials for Geothermal and Petroleum Drilling: A Critical Review of Mechanisms, Applications, and Future Perspectives in High-Temperature Fractured Formations.

Geothermal energy, as a clean and renewable energy source, has attracted widespread attention. However, severe drilling fluid lost circulation (LC) during geothermal drillingparticularly under high-temperature, wide-fracture conditionsremains a critical challenge. Conventional lost circulation materials (LCMs) exhibit notable limitations when confronted with complex loss scenarios: rigid bridging particles poorly conform to downhole fractures; superabsorbent resins impair drilling fluid rheology and yield insufficient plug strength; and chemical gels suffer from high-temperature degradation and uncontrollable gelation times. These deficiencies are especially pronounced in high-temperature, highly fractured geothermal reservoirs, underscoring the urgent need for novel smart LCMs capable of self-adapting to fracture apertures while maintaining compatibility with drilling fluids. Plugging shape memory polymers (SMPs) have demonstrated considerable application potential in the field of intelligent LC control owing to their temperature-responsive shape-recovery behavior. This review systematically summarizes the mechanisms, programming methods, and LC plugging applications of SMPswith particular emphasis on high-temperature, wide-fracture geothermal environmentsas well as recent advances in thermoplastic elastomers. Current deficiencies in high-temperature adaptability and deplugging mechanisms are identified, and future design directions for smart LCMs intended for extreme conditions (150-300 °C) are proposed.