High-Compression-Resistant Thermosetting Resins as Plugging Materials for Oil-Based Drilling Fluids

Introduction: Lost circulation during drilling, especially in ultra-deep and deep wells, poses significant operational challenges due to great formation pressures and complex fracture networks. Conventional Lost Circulation Materials (LCMs) often lack sufficient pressure resistance and compatibility with oil-based drilling fluids. Methods: This study developed a high-compression-resistant thermosetting resin as a novel LCM by curing epoxy resins. The material's structure and properties were categorized using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), and compressive strength testing. Plugging efficiency was evaluated using 3Dprinted core models with fracture widths ranging from 3–2 mm, 4–3 mm, and 2–1 mm. Results: The resin-based LCM exhibited irregular particle shapes (0.15–3.2 mm), thermal stability up to 300°C, and a compressive strength of up to 140 MPa. The material demonstrated strong compatibility with oil-based drilling fluids, producing minimal changes in rheological properties and reducing High-Temperature High-Pressure (HTHP) fluid loss by 33%. Optimized particle gradation significantly improved sealing across fracture sizes, forming dense and effective sealing zones. Discussion: The material's mechanical strength and thermal resistance enhance its performance in high-stress, high-temperature environments. Its broad particle size distribution facilitates bridging and complete sealing in complex fractures, making it particularly effective for deep well applications. Conclusion: The developed epoxy resin-based LCM offers improved pressure resistance, thermal stability, and compatibility with oil-based drilling fluids, presenting a promising solution for mitigating lost circulation in complex formations.