Performance Evolution and Regulation of Bentonite-Based Drilling Fluids Under Representative Complex Conditions: A Review

As a core functional component of water-based drilling fluids, bentonite plays a critical role in regulating rheology, suspension capacity, filtration performance, and wellbore stability through its hydration, dispersion, and structure-building behavior. With drilling extending into deep, ultra-deep, and complex formations, harsh conditions such as high temperature, salt contamination, pH fluctuation, and variations in solids content can significantly alter bentonite behavior, resulting in rheological instability, weakened suspension capacity, increased fluid loss, and deterioration of filter-cake quality. However, existing studies have often focused on individual additives or specific operating conditions, while a systematic understanding of bentonite performance evolution and corresponding regulation strategies remains limited. This review summarizes the types, basic characteristics, and engineering functions of bentonite in water-based drilling fluids, and discusses the performance changes in bentonite-based systems under high-temperature conditions, salt contamination, pH variation, and changes in bentonite solids content. On this basis, the main regulation approaches are categorized into fluid-chemistry regulation, functional-additive regulation, and solid-phase composition regulation, with emphasis on their effects on rheological behavior, suspension stability, fluid-loss control, and filter-cake quality. Relevant performance evaluation and characterization methods are also summarized. This review provides a systematic framework for understanding and regulating bentonite-based drilling-fluid performance under complex operating conditions and offers guidance for formulation design and engineering optimization.