Synthesis and Application of a Temperature Sensitive Poly(Acrylamide-Co-N-Isopropylacrylamide-Co-Sodium P-Styrene Sulfonate) as a New Water-Based Drilling Fluid Plugging Agent

In the process of oil and gas production, the failure of drilling fluid caused it to invade the formation, leading to wellbore instability. N-isopropylacrylamide (NIPAM), acrylamide (AM), and sodium p-styrene sulfonate (SSS) were used as raw materials, and the P(NIPAM/AM/SSS) (abbreviated as NAS) temperature-sensitive plugging agent was synthesized by inverse emulsion polymerization. The optimum synthesis conditions were obtained using a redox initiation system. Infrared measurements and UV–visible analysis showed that the target product was successfully prepared, and NAS exhibited a lower critical solution temperature (LCST) of 55°C, with sensitive temperature-responsive behavior. Rheological and filtration tests, along with high-temperature and high-pressure (HTHP) sand tray tests, demonstrated that the temperature-sensitive plugging agent effectively plugged the formation. Particle size analysis and Zeta potential analysis indicated that the addition of the temperature-sensitive plugging agent increased the electrostatic stability of bentonite-based slurry and polymer. Contact angle measurements and micro-morphology of the mud cake revealed that a hydrophilic-hydrophobic transition occurred at high temperatures in NAS, forming a dense hydrophobic film on the surface of the mud cake. This film effectively sealed cracks and micropores, reduced the invasion of free water, and improved wellbore stability.