Nano-Grafted Acrylamide Copolymer as an Anti-Temperature and Anti-Calcium Fluid Loss Agent for Water-Based Drilling Fluids

When the well bottom temperature rises owing to increased well depth and formation complexity, the inadequacies of naturally modified polymeric fluid loss agents were revealed one by one, and synthetic polymeric fluid loss agents emerged as the essential technology to handle these problems. Nanomaterials were gradually being employed to increase the performance of polymeric fluid loss agents. Through free radical polymerization of amide polymers with silica nanoparticles in aqueous solution, a novel nano-graft copolymer (AAN-g-SiO2) was prepared for usage as a water-based drilling fluid loss agent. Fourier transform infrared spectroscopy and thermogravimetric analyses were used to investigate the structural characteristics and thermal stability of the polymer chains. Then, 4% bentonite freshwater-based mud and different concentrations of NaCl/CaCl2-based mud were prepared and added to the fluid loss agent AAN-g-SiO2. Moreover, high-temperature aging was carried out, and the API filtration volume of base mud and rheological characteristics were assessed. The fluid loss agent was demonstrated to withstand a high temperature of 220 °C, with the freshwater-based mud filtration volume at this temperature being 13.25 mL. Also, at 180 °C, AAN-g-SiO2 could be resistant to calcium and salt. Finally, we addressed the mechanism of AAN-g-SiO2 filtration using scanning electron microscopy and zeta potential distribution. The results showed that the inclusion of AAN-g-SiO2 may increase the stability of the drilling fluid system, resulting in the production of a thin and dense filter cake with no folds or pores visible at the microscopic level.