Abstract
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 °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.
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