Preparation and Evaluation of Nanopolymer Microsphere Plugging Agents for Ultrahigh-Temperature Water-Based Drilling Fluids

With oil and gas drilling going deeper, wellbore instability and high-temperature failure of drilling fluid become more and more serious. Using plugging agents to block micropore and microfracture formation is the key to minimizing filtrate invasion into the formation, stopping pressure transfer, and reducing downhole accidents. At present, the most commonly used plugging agents are hardly able to satisfy the plugging demands of ultrahigh-temperature formation. A high thermo-resistant nanopolymer microsphere (PSDA) was prepared by soap-free emulsion polymerization. The study indicated that the starting thermal breakdown temperature of PSDA was 316 °C. At the indoor temperature, the median particle size (D50) was 177 nm. After aging at 240 °C, D50 reduced to 152 nm. Meanwhile, it can be observed from the scanning electron microscope (SEM) that the particle size of PSDA has little difference before and after high-temperature effect, indicating that PSDA possesses excellent stability against high temperatures. The turbiscan stability index (TSI) values of 3 wt % PSDA suspensions were less than 0.1, which has good dispersion stability. The blocking performance of the PSDA suspension was studied using 100 and 300 nm microporous filter membranes as blocking media. With the addition of PSDA in the drilling fluid, API filtration gradually decreases. When the addition amount was 3 wt %, after aging at 240 °C, the reduction rate of API filtration was 57.6%, and the filter cake formed was dense. At the same time, a great quantity of microspheres on the filter cake surface can be observed in the SEM picture, indicating that PSDA can resist high temperatures at 240 °C and has good filter loss reduction performance. Compared with emulsified bitumen, nanopolyester (NP-1), and silicone sol (JN-40), PSDA has the best filtration reduction performance. PSDA holds promise as an excellent temperature-resistant plugging additive for water-based drilling fluid.