Experimental Study of a Self-Aggregating Agent for Formation Plugging While Drilling in Medium-Permeability Reservoirs

Summary Preemptive plugging of formation micropores and fractures with functional materials is critical for lost circulation prevention. Single rigid or flexible plugging materials have inherent drawbacks, while rigid-flexible composites show superior plugging strength, high-temperature (HT) resistance, and better adaptability to formation pore/fracture geometries. However, conventional rigid-flexible composites rely on physical bridging of rigid particles and passive filling of flexible shells, lacking a robust internal network and leading to plugging layer instability. Although chemical adhesion is adopted to improve integrity, the limitation of passive accumulation remains unsolved. To fundamentally enhance plugging layer stability, we propose in this work an autonomous, rapid, and intelligent aggregation design strategy to break through the conventional passive accumulation mode. A novel plugging agent SDB-1 was synthesized, with calcium carbonate (CaCO3) as the rigid core and a copolymer of γ-methacryloxypropyl trimethoxysilane (KH570), glycidyl methacrylate (GMA), and acrylic acid (AA) as the flexible shell. Its filtration control and plugging performance were systematically evaluated with multiple porous media, and the optimal application concentration was determined as 2 wt%. SDB-1 effectively reduces fluid loss through membranes and sand disks under high-temperature and high-pressure (HTHP) conditions, with a plugging efficiency of 85.24% for 40/60-mesh quartz sand seepage channels. Mechanism analysis shows that SDB-1 particles realize autonomous aggregation driven by van der Waals forces and hydrogen bonds. After rigid core bridging, the softened flexible shell fills microgaps; hydroxyl (-OH) and carboxyl (-COOH) groups form hydrogen-bond networks and interact with formation minerals, enhancing interfacial bonding and plugging stability. SDB-1 was successfully applied in Well Mi37-2MH of the Ordos Basin, exhibiting excellent performance in controlling coal seam seepage loss.