To address the challenges of micro-fracture development in shale formations, frequent wellbore instability, and the limited plugging capability of water-based drilling fluids in unconventional reservoirs, a nano-plugging agent (NPA) was synthesized using emulsion polymerization. The synthesized NPA was characterized through thermogravimetric analysis (TGA) and transmission electron microscopy (TEM), revealing excellent high-temperature stability and a spherical or sub-spherical morphology, with particle diameters ranging from approximately 20 to 50 nm. The rheological, filtration, and plugging properties of NPA were systematically evaluated, and its sealing mechanism was analyzed. The results demonstrate that at a test temperature of 180 °C, the optimal NPA concentration in the drilling fluid base slurry is 1.5%, achieving a 60.5% reduction in HTHP (high-temperature high-pressure) sand disc filtration loss. Additionally, the API filtration loss and HTHP filtration loss reduction rates reached 58.1% and 50.3%, respectively, highlighting the remarkable filtration loss reduction and plugging efficiency of NPA under high-temperature conditions. After NPA treatment, the specific surface area and pore volume of shale cuttings decreased to 9.348 m²/g and 0.035 cm³/g, respectively, indicating effective surface plugging. The mechanism analysis suggests that due to its nanoscale size, NPA can penetrate deep into micro-pores and fractures within the shale, achieving deep-layer plugging. Furthermore, NPA forms a physical plugging barrier on the shale surface, effectively suppressing shale hydration and swelling. This study provides valuable insights and guidance for addressing wellbore instability and the insufficient plugging performance of drilling fluids in unconventional reservoir drilling operations.

The issue of fluid loss in fractured formations presents a significant challenge in petroleum engineering, often leading to increased operational costs and construction risks. To address the limitations of traditional lost circulation materials (LCMs) in oil reservoirs with different fracture sizes, this study developed an acrylic resin gel particle with excellent thermal stability (thermal decomposition temperature up to 314 °C) and compatibility. By employing Box–Behnken design and response surface methodology, the synergistic interaction of calcium hydroxide (Ca(OH)₂), asbestos fibers, and cement was optimized to create a novel gel solidification plugging system that meets the requirements of fluid loss control and compressive strength improvement. Experimental results revealed that the gel-based system demonstrated exceptional performance, achieving rapid fluid loss (total fluid loss time of 18~47 s) and forming a high-strength gelled filter cake (24 h compressive strength up to 17.5 MPa). Under simulated conditions (150 °C), the gel-based system provided efficient fracture sealing, showcasing remarkable adaptability and potential for engineering applications. This study underscores the promise of acrylic resin gel particles in overcoming fluid loss challenges in complex fractured formations.