Development of High-Thermal-Conductivity Inhibitive Drilling Fluid with Nano-CuO and Cationically Modified Poly(Vinyl Alcohol).

This study addresses wellbore instability during drilling in water-sensitive formations by enhancing the heat-transfer performance of an inhibitive drilling fluid. CuO nanoparticles (NCs) were introduced into a drilling fluid containing cationically modified poly-(vinyl alcohol) (PVAG), which was synthesized by grafting 2,3-epoxypropyl trimethylammonium chloride (GTMAC) onto poly-(vinyl alcohol) (PVA). The compatibility between NCs and PVAG was evaluated, and the mechanism by which PVAG and NCs affected the inhibitory performance of drilling fluids was investigated. The results indicated that GTMAC was successfully grafted onto PVA via ether bonds. Compared with soaking in PVA, soaking in 1.5% PVAG reduced the interlayer spacing of bentonite to 1.251 nm and decreased its dispersibility. The quaternary ammonium groups from GTMAC accelerate the adsorption of PVA onto the clay surface by neutralizing its negative charges, thereby reducing the electrostatic repulsion between crystal layers and suppressing clay lattice expansion. Mechanistically, the NCs reduce water infiltration to assist PVAG in improving the inhibitory performance of the drilling fluid, while PVAG stabilizes the suspension of NCs to construct a thermal conductivity network that substantially improves the heat-transfer performance. Together, NCs and PVAG synergistically improve the inhibitive and heat-transfer properties of drilling fluids. The findings of this study can provide a reference for the selection of drilling fluid systems in complex formations and deep well drilling.