Preparation and Mechanism Study of Resistant to High Temperature and High Salt Hyperbranched Fluid Loss Reducer for Water-Based Drilling Fluid

Abstract It is difficult to regulate the flow and filtration characteristics of water-based drilling fluids(WBDFs) in complex formation conditions such as extreme thermal conditions, elevated pressure environments, and hypersaline circumstances. Conventional fluid loss reducer) are mainly linear structure polymers, which have large self-viscosity and have a great impact on the flow and filtration characteristics. In ultra-high temperature and hypersaline circumstances, polymer molecular chains are prone to conformational changes such as crosslinking and twisting, resulting in uncontrollable rheological characteristics of drilling fluids and increased leak-off volume, Cause drilling accident. Aiming at a series of problems of conventional linear fluid loss reducer. In this paper, HBPSi was prepared by transesterification polycondensation reaction using 3-aminopropyl triethoxysilane and 1, 4-butanediol as reactants. Then HBPSi, N,N-dimethyl acrylamide, 2-Acrylamido-2-methylpropane sulfonic acid, dimethyl diallyl ammonium chloride, 1-vinyl-2-pyridone as copolymers, cerium ammonium nitrate as initiator, and water as dispersed phase were used as copolymers, hyperbranched fluid loss reducer HBPSi-DADN was prepared by free radical polymerization. The results show that hyperbranched fluid loss reducer HBPSi-DADN has a highly branched three-dimensional structure, low viscosity and high stability. When 3 wt% HBPSi-DADN is added to the drilling fluid base mud, apparent viscosity is 48mPa·s, apparent viscosity increment was relatively small. When 3 wt% HBPSi-DADN and 30% NaCl are added into drilling fluid base mud, the drilling fluid system exhibited a decrease in apparent viscosity from 26 mPa·s to 23 mPa·s following thermal aging at 200°C, The system viscosity remained relatively stable with no significant alterations observed after thermal aging at 200°C, the high temperature and high pressure filtration loss after aging at 200 °C is only 22mL. Due to its unique three-dimensional branching structure, the hyperbranched fluid loss reducer HBPSi-DADN is easier to interact with bentonite, facilitating stable dispersion, improving overall drilling fluid performance, and promoting the formation of compact filter cake. Compared with linear fluid loss reducer, the hyperbranched fluid loss reducer HBPSi-DADN has excellent temperature and salt resistance, and effectively solves problems of difficult rheological control and significant fluid loss phenomena in drilling fluid systems under high-temperature and high-salinity environments.