Multi-Scale Regulation of High-Temperature and High-Salinity Water-Based Drilling Fluids

Deep and ultra-deep well drilling subjects water-based drilling fluids (WBDFs) to multiple simultaneous disturbances: elevated temperature, high salinity, high-density solids and acid gas contamination. Conventional studies usually classify materials separately as “polymers, nanomaterials and bio-based materials”, yet this makes it difficult to explain why the same material behaves so differently in different base muds and evaluation protocols, and equally difficult to handle the trade-offs among rheology retention, fluid-loss control, plugging and wellbore stability. In this work, the 61 full texts provided by the user served as the candidate pool; after title-and-abstract screening and full-text review, 46 were included, of which 33 served as core evidence. The studies on high-temperature, high-salinity WBDFs are reorganised across five scales: molecular structure, particle interface, mesoscopic network, filter-cake/wellbore barrier, and engineering performance. The analysis shows that high-temperature, high-salinity failure is not a single “polymer degradation” event, but a continuous process comprising clay dehydroxylation and loss of hydrophilicity, electrical double-layer compression, polymer chain coiling or desorption, particle aggregation, and pore interconnection within the filter cake. Temperature- and salt-tolerant polymers synergistically maintain hydration, adsorption and steric hindrance through sulfonate groups, zwitterions, rigid rings, polyether side chains and hydrophobic association structures; nano- and organic–inorganic composites rely on dispersion stability and particle-size grading to build low-permeability filter cakes; natural polymers must undergo hydrophobisation, grafting, crosslinking or compositing to cross the boundary of harsh conditions; and thermo-responsive, self-healing and film-forming materials are driving the transition of these systems from passive tolerance to on-demand response. The main bottleneck in the current evidence is not a shortage of new materials, but the inconsistency of base-mud composition, aging regimes, salt type, measurement temperature and HTHP conditions, which makes reported performance figures non-comparable across studies and leaves long-term cycling, combined contamination and field validation insufficiently addressed. Future work should focus on standardised multi-factor evaluation, in-situ multi-scale characterisation, data-driven formulation optimisation, full-life-cycle green assessment, and material–system–formation co-design.