Lost Circulation and Plugging of Oil-Based Drilling Fluids: A Review of Theories, Methodologies, Materials, and Future Perspectives

Oil-based drilling fluids (OBDFs) are now the dominant working fluids in deep, ultradeep, and unconventional oil and gas reservoirs, mainly because of their high-temperature resistance and strong inhibition. Nevertheless, lost circulation drastically reduces the drilling efficiency and hydrocarbon recovery. This review systematically summarizes research progress regarding lost circulation mechanisms, plugging theories, material design theories, and characterization methodologies for the evolution of plugging layers in OBDFs while elaborating on the applicable scenarios and inherent limitations of each theory and technique. It comprehensively discusses the performance and field application of physical, chemical, and smart responsive lost circulation materials (LCMs) tailored for oil-based systems and proposes suggestions for future development. Studies reveal that current theories of lost circulation mechanisms, plugging, and material design lack a unified and complete framework, and methods for characterizing the evolution of plugging layers still have substantial deficiencies. Dynamic plugging experiments coupled with microscopic numerical simulations are now the mainstream approach in lost circulation evaluation. Current plugging materials generally suffer from limited applicability, insufficient temperature resistance, and poor compatibility with oil-based systems. Future work must advance the integrated development of theories, materials, and field applications across multiple dimensions so that lost circulation in OBDFs can be efficiently controlled.