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.