Synthesis and performance evaluation of a novel polymeric fluid loss controller in water-based drilling fluids: High-temperature and high-salinity conditions

Fluid loss prevention is a crucial factor in oil and gas drilling operations. In water-based drilling fluids, often called drilling muds, the colloidal structure made by bentonite begins to thicken upon exposure to high salinity conditions, especially when an excessive temperature is encountered. The consequences are a considerable increase in the filtration volume and poor rheological properties. In this study, a novel terpolymer, AAV, was synthesized by acrylamide (AM), 2-acrylamide-2- methylpropane sulfonic acid (AMPS), and 1-vinylimidazole (VI) to be used as a fluid loss controller. AAV was characterized by the proton nuclear magnetic resonance (H-1-NMR) and Fourier transform infrared spectroscopy (FTIR). Based on the thermal gravimetric analysis (TGA), AAV was thermally stable up to 300 degrees C. The performance of AAV was explored according to API standard procedure. Under saturated-salt contamination, the bentonite-based fluid exhibited a fluid loss volume of 111 ml and 245 ml and a filter cake thickness of 2.7 mm and 2.9 mm at 26 degrees C and 100 degrees C, respectively. After thermally aging the muds even up to 180 degrees C, AAV performed best in the filtration control, allowing filtration volume in the range of 1.4 ml-6.5 ml. It also left a much thinner filter cake, 0.21 mm-0.79 mm. SEM images showed a much smooth, untracked, and compact filter cake for the mud samples treated by AAV. The addition of the terpolymer to bentonite dispersion decreased the value of the zeta potential by 5 mV, indicating an improvement in the stability of the dispersion. From the rheological analysis, AAV increased the viscosity of bentonite-based mud under saturated-salt contamination. The interaction between AAV and bentonite was revealed by FT-IR spectra. The filtration control mechanisms of AAV are hypothesized through the deflocculation of montmorillonite (Mt) particles, the formation of a chelate complex with cations, and surface adsorption of onto Mt particles.