Ultra-High Temperature Resistant and Environmentally Friendly Polymer Water-Based Drilling Fluid: Development, Performance Evaluation, and Field Application

Abstract

Global oil and gas exploration is increasingly moving towards deeper formations. However, under the complex and harsh conditions of ultra-high temperature, high pressure, and salt-gypsum layers, the performance of conventional water-based drilling fluids deteriorates significantly, leading to frequent drilling incidents and posing a core technical challenge to the efficient exploitation of deep hydrocarbon resources. Through theoretical and material innovation, this study pioneers a molecular design methodology that synergistically combines strong adsorption groups with a hyperbranched structure, micro-crosslinked network, heterocyclic rings, and nano-composites to enhance the ultra-high temperature and salt tolerance of drilling fluid additives. Based on this methodology, two key additives were synthesized: a hyperbranched polymer fluid loss reducer with superior adsorption capabilities and an organic-inorganic hybrid microsphere plugging agent designed to effectively seal micro-fractures in the formation. A high-performance polymer water-based drilling fluid system was developed with these two additives as core components. The developed drilling fluid system demonstrated exceptional stability and performance under simulated extreme downhole conditions of 240°C, saturated salt contamination, and a density of 2.4 g/cm3. After dynamic thermal aging at 240°C for 16 hours, the fluid exhibited excellent rheological stability and a remarkably low high-temperature, high-pressure fluid loss volume of less than 20 mL. Long-term aging tests confirmed that its key properties remained stable for over 10 days, indicating outstanding resilience for extended drilling operations. Beyond its superior technical performance, the system offers significant practical and environmental benefits. The entire formulation relies on a concise suite of no more than five key additives, simplifying logistics and onsite maintenance. Critically, it is formulated without any sulfonated materials or highly toxic components, which eliminates the risk of hydrogen sulfide generation at high temperatures, making the system exceptionally safe and compliant with stringent environmental regulations, suitable for use in environmentally sensitive regions. The system was successfully deployed in the deepest section of 10,000-meter scientific exploration well, SDTK 1, playing a critical role in its safe and efficient drilling. By introducing a groundbreaking molecular design strategy, this work developed a robust, practical drilling fluid system that successfully integrates ultra-high temperature resistance, high-density tolerance, and exceptional environmental adaptability, providing a high-performance, cost-effective, and eco-friendly technical solution for global ultra-deep oil and gas drilling operations.