Synthesis and Performance Evaluation of a High-Temperature Salt-Resistant Fluid Loss Additive.

To address the challenges encountered in drilling operations for high-temperature and high-salinity hydrocarbon reservoirs, this study successfully designed and synthesized a novel organic-inorganic core-shell structured fluid loss control agentDH. This material features rigid calcium carbonate nanoparticles as the core, encapsulated by a copolymer shell of acrylamide (AM) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS). This unique structure is designed to fundamentally enhance the thermal stability and salt tolerance compared to conventional pure polymer treatments, by restraining the curling and decomposition of polymer chains under extreme conditions. Characterization results confirmed the successful construction of the core-shell structure and demonstrated excellent thermal stability. Performance evaluation showed that DH maintains outstanding fluid control performance even after exposure to high temperature (200 °C), high salt concentration (15% NaCl), and multiple aging cycles. Compared to the base fluid, DH reduces fluid loss by over 95%. More importantly, its performance significantly surpasses that of conventional agents (e.g., PAC); under similarly harsh conditions where the latter fails (fluid loss >25 mL), DH stably controls the API fluid loss below 7 mL. Mechanism studies revealed that efficient fluid control is achieved because DH, with its uniform particle size distribution (matching filter cake pore sizes) and large specific surface area, effectively plugs filter cake micropores, thereby forming a compact, low-permeability filter cake. This study provides an innovative and effective solution for developing next-generation drilling fluid additives suitable for extreme operating conditions.