Experimental study of a novel oil-based crosslinking-curing lost circulation material for shale gas well

In the process of shale gas well drilling in the southern Sichuan Basin, China, lost circulation of high-density oil-based drilling fluid has become a main challenge. In this study, a novel oil-based crosslinking-curing lost circulation material (OBCC-LCM) system applicable for 100-150 degrees C shale formation was developed based on polyether, isocyanates and blocking agent. The performance of OBCC-LCM pills was comprehensively evaluated by testing fluidity, setting time, strength, elasticity and fracture sealing capacity. The OBCC-LCM pill setting time could be controlled in 70-120 min. The strength of the pill solid was 5.27-6.51 MPa after 360 min heating, and the volume almost restored to the original states after being compressed by 70%. The pill sealed fractures up to 5 mm wide under a differential pressure of 5.2-6.1 MPa, and a higher maximum fracture sealing capacity when being jointly used with bridging LCMs. The OBCC-LCM clearly demonstrated superior performance of good pumpability at room temperature, stability under high temperature, compatibility with oil-based drilling fluids, adaptability with various fracture widths and sustainability in induced fracture. It is suitable for curing loss of induced fracture in low permeability formation and loss of oil-based drilling fluid, especially for loss of oil-based drilling fluid in shale formations.