Development and Application of a Novel Nano-Micron Plugging Agent with Core-Shell Structure for Oil-Based Drilling Fluids

China is rich in Shale gas resources, and the preliminarily predicted geological resource reserves are about 134 1012 m3, with a technically recoverable reserve of approximately 25·10¹² m³. The Weiyuan-Rongxian area has abundant natural gas resources, but its geological conditions are complex, characterized by poor drillability of local formations, deep burial of reservoirs, and uneven horizontal distribution. These complex geological conditions result in low mechanical drilling speed, long drilling cycles, and high drilling costs, posing severe challenges and challenges to drilling engineering. In view of the technical difficulties of oil-based drilling fluid in the deep shale high-pressure fracture formation in this block, this paper has developed a particle size variable nano micron plugging agent CLG-NM suitable for the high-pressure fracture formation in the deep shale gas formation. Its molecular structure was characterized, its nano micron plugging characteristics were evaluated, and its microscopic mechanism was discussed. The research results indicate that the median particle size D₅₀ of the newly developed variable nano micron sealing agent CLG-NM is 89.4 nm. After high-temperature aging at 150°C, the filtration loss of the experimental slurry showed a gradually decreasing trend with the increase of the amount of sealing agent CLG-NM added. When the dosage of sealing agent is 1%, the filtration loss of sand disc sealing is only 4.2 mL, demonstrating strong nano micron sealing performance. On this basis, CLG-NM was applied on-site in the Longmaxi Formation of Well Weiye 32-3HF. Field tests have shown that during the drilling process of the Weiye 32-3HF Longmaxi Formation, there were no complex downhole situations such as well leakage or wellbore instability. The drilling was successfully completed, with a pure drilling time of 42 hours, an average drilling speed of 7.81 m/h, and a density reduction of about 0.08-0.1 g/cm³ compared to the adjacent well.