Advancements in high-temperature and environmentally friendly water-based drilling fluids for horizontal wells

Abstract Against the backdrop of the global energy transition toward green and low-carbon development, the exploitation of unconventional oil and gas resources has become a strategic priority worldwide. This critical review systematically summarizes the state-of-the-art progress of high-temperature, eco-friendly water-based drilling fluids (WBDFs), with a focused discussion on three core categories of functional additives: modified natural polymers, synthetic polymers, and organic–inorganic nanocomposites. Natural polysaccharides (e.g., guar gum, xanthan gum) achieve improved thermal stability through functional group grafting and hydrophobic association modification. Synthetic polymers – especially zwitterionic polyelectrolytes and amphiphilic copolymers – deliver outstanding performance in high-temperature and high-salinity (HT/HS) environments, benefiting from rigid carbon backbones and self-charge compensation mechanisms. Nanostructured biopolymers and polymer-nano hybrid networks collectively enhance thermal endurance, salt tolerance, and shear resistance. This work clarifies standardized scaling rules for converting laboratory-measured WBDF performance metrics to field engineering practice, and characterizes typical HT-triggered performance deterioration behaviors of the three additive families. Representative eco-friendly fluid systems, including HPWBM, MEG-WBM, and synthetic-based drilling fluids, have achieved successful field deployment in shale-gas horizontal wells and deepwater drilling projects. Green nanocomposites maintain uniform dispersion and favorable interfacial compatibility under extreme HT/HS conditions. Future research directions are proposed as follows: developing intrinsically heat-resistant materials with thermal tolerance exceeding 200 °C; optimizing nanocomposite interfaces via three core technical routes (nanoparticle surface functionalization, silane coupling agent modification, and core–shell structural construction); and developing digitally intelligent adaptive WBDF design frameworks.