A Hyperbranched Copolymer as High-Temperature and Salt-Resistance Fluid Loss Reducer for Water-Based Drilling Fluids: Preparation, Evaluation, and Mechanism Study

Summary In the high-temperature and high-salt environment of deep and ultradeep wells, conventional linear polymer fluid loss reducers for drilling fluids have high viscosity and are prone to conformational changes (such as curling, crosslinking, and degradation), posing significant challenges to the control of drilling fluids performance (e.g., viscosity, filtration, weighting). We developed an innovative high-temperature and high-salt-resistance hyperbranched copolymer fluid loss reducer (HBPSiO-DADV) using N, N-dimethylacrylamide (DMAA), 2-acrylamide-2-methylpropyl sulfonic acid (AMPS), diallyl dimethyl ammonium chloride (DMDAAC), and 1-vinylimidazole (VIm) through the initiation polymerization of cerium ammonium nitrate (CAN) and hyperbranched polysiloxane with amino and hydroxyl groups at the end. For comparison, a linear copolymer fluid loss reducer (DADV) was prepared by initiating monomer polymerization in equal proportions using an oxidation-reduction system composed of ammonium persulfate (APS) and sodium bisulfite. Compared with DADV, HBPSiO-DADV has significantly lower molecular weight and relatively lower solution viscosity. Thermogravimetric analysis (TGA) revealed that the initial degradation temperature of HBPSiO-DADV (295°C) was obviously superior to that of DADV (258°C), indicating that the hyperbranched copolymer had excellent temperature resistance. When 3 wt% HBPSiO-DADV was added to the base slurry, the apparent viscosity (AV) before and after aging at 200°C was 45 mPa·s and 39 mPa·s, respectively, values that were significantly lower than those of DADV (80 mPa·s and 50 mPa·s, respectively). In addition, after aging at 200°C, the salt-contaminated base slurry [30 wt% sodium chloride (NaCl)] containing 3 wt% HBPSiO-DADV had a high-temperature and high-pressure filtration loss of 21 mL, which was notably lower than that of DADV (30 mL) at the same concentration, as well as that of commonly used anti-high-temperature fluid loss reducers such as Driscal-D (52 mL) and Dristemp (58 mL). Therefore, the unique hyperbranched structure of HBPSiO-DADV endowed it with excellent performance in low viscosity, temperature, and salt resistance, which would point out new directions for the design and manufacture of high-performance drilling fluids treatment agents and provide strong support for the regulation of rheological and filtration properties in deep and ultradeep wells.