Application of environmentally friendly amphoteric polyacrylamide hydrophobically modified with plant oil as additive in water-based drilling fluid

Abstract

Hydrophobic associating polymers show great potential in formulation of high-performance drilling fluids, due to their hydrophobic associative ability in high-temperature and high-salt conditions. Herein, a novel amphoteric polyacrylamide of poly(acrylamide/2-acrylamido-2-methyl-1-propanesulfonic acid/methylacrylethyl trimethylammonium chloride) hydrophobically modified with epoxidized soybean oil denoted as PAADE was prepared and applied in water-based drilling fluid, and one without hydrophobic modification (PAAD) was also used for comparison. Compared with PAAD, PAADE displayed characteristic association behavior with a critical association concentration (CAC) of 0.3 w/v%, and a salt thickening phenomenon over 3 w/v% NaCl concentration. The impacts of PAADE and PAAD on rheological and filtration properties of bentonite-based drilling fluid (BTDF) were evaluated under different salinity. The fitted Herschel-Bulkley rheological parameters indicated that BTDF containing PAADE showed stronger yield stress, easier flowability and better salt resistance at a reasonable concentration below CAC. Meanwhile, PAADE largely reduced the fluid loss of BTDF before and after thermal aging at 150°C, showing high temperature tolerance. The addition of NaCl promoted larger reduction of filtration. The superior properties of PAADE in BTDF were revealed to be the competitive results of salt-induced hydrophobic association and inter-particles configuration transition. Moreover, the incorporation of epoxidized soybean oil improved the biodegradability of PAADE.