Development and performance evaluation of a high temperature resistant, internal rigid, and external flexible plugging agent for water-based drilling fluids

During the drilling process for oil and gas production, a larger number of drilling fluids invade the formation, causing severe formation damage and wellbore collapsing, which seriously hinders the efficient production of deep oil and gas. Although several plugging agents have been developed for efficient fracture sealing in recent years, the development of high-performance plugging agents with self-adaptive ability and high-temperature resistance remain a challenge. Herein, we report the synthesis of an internal rigid and external flexible plugging agent PANS by reversed-phase emulsion polymerization with nano-silica as the rigid core and poly (acrylamide-co-N-vinylpyrrolidone) as a flexible shell. The plugging agent has a median particle size of 10.5 μm and can self-adapt to seal the microfractures and fractures in the formation, leading to an effective reduction in the filtration loss of bentonite water-based drilling fluid under both low temperature and low pressure (LTLP) and high temperature and high pressure (HTHP) conditions. In addition, compared with the neat nano-silica (500 nm), the sealing efficiency of PANS toward 100–120 mesh sand bed was increased by 71.4% after hot rolling at 180°C.