Nanolaponite/Comb Polymer Composite as a Rheological Modifier for Water-Based Drilling Fluids

During the drilling of deep/ultradeep wells, water-based drilling fluids (WBDFs) often experience harsh conditions of ultrahigh temperature and high salt. Ultrahigh temperatures and high salts cause rheological instability in drilling fluid, reducing its suspension and cutting-carrying capacity. In this study, a comb polymer, P-TPEG with isopentenol polyoxyethylene ether (TPEG) as the side chain, was prepared via free radical polymerization in an aqueous solution and then compounded with nanolaponite (LAP) to obtain a composite rheological modifier (LAP/P-TPEG). In situ Fourier transform infrared spectroscopy and thermogravimetric analysis showed that LAP/P-TPEG had an excellent thermal stability. The LAP/P-TPEG solution test showed a shear thinning behavior. The results demonstrate that LAP/P-TPEG can improve the rheology of WBDFs before and after aging at 240 °C and can resist 15 wt % NaCl. LAP/P-TPEG formed a strong adsorption with bentonite through hydrogen bonds and electrostatic interactions. LAP, P-TPEG, and bentonite formed a “reversible” “dual” spatial network structure in WBDFs, improving the rheology and the suspension, cutting-carrying, and wellbore-cleaning abilities of the drilling fluid under ultrahigh temperature and high salt.