Lost circulation mechanism and control technology in the Emeishan Basalt, Daxingchang structure

Severe lost circulation frequently occurs while drilling Emeishan Basalt in the Daxingchang Structure of Sichuan Basin. Conventional bridging plugging has low one-time success rate and frequent leakage recurrence, which restricts safe and efficient drilling. Based on field leakage data, core fracture observation and mineral composition analysis, this paper clarified the basalt leakage mechanism dominated by brittle rigid mineral fracture networks with strong drilling fluid density sensitivity. The particle size distribution, compressive crushing resistance and high-temperature abrasion performance of conventional lost circulation materials were systematically evaluated. A high-temperature self-healing chemical adhesive compatible with oil-based drilling fluid was prepared using PTMEG, PPDI, DBTDL and MPDS, which can tightly cement bridging particles and formation rock. Targeted plugging formulas were optimized for different leakage rates. The experimental results show that all optimized plugging systems with chemical adhesive reach a pressure-bearing capacity of 20 MPa, realizing a qualitative shift from physical bridging to chemical integrated bonding. This technology system provides effective technical support for lost circulation control in Emeishan Basalt of the Daxingchang Structure.