Functional Construction and Comprehensive Performance Evaluation of a 180 °C-Resistant Non-Sulfonated Water-Based Drilling Fluid System

Aiming at the industrial problems of traditional sulfonated drilling fluids in high-temperature drilling of deep oil and gas reservoirs at 180°C, including high-temperature degradation, poor environmental protection, and severe reservoir damage, this paper adopts a function-oriented research idea to construct a set of non-sulfonated water-based drilling fluid systems with excellent comprehensive performance and temperature resistance up to 180 °C. Strict screening criteria for single agents were established, and six core non-sulfonated treatment agents were selected from 18 candidate agents in four categories: viscosifiers, fluid loss reducers, inhibitors, and high-temperature stabilizers. The compounding synergistic effects of cross-category treatment agents were studied, and four core action mechanisms were revealed. The optimal formula was obtained through optimization. Tests show that after hot rolling at 180 °C for 16 h, the system has an apparent viscosity retention rate of ≥81%, a yield point retention rate of ≥76%, and a high-temperature and high-pressure filtration loss of ≤12.8 mL. It can resist 15% salt, 1.0% calcium, and 15% drill cuttings, and maintains stable performance under composite pollution. At 180 °C, the shale linear expansion rate is only 8.6%, and the cuttings rolling recovery rate reaches 92.4%. The core permeability recovery value is ≥90.2%, the biotoxicity EC50 value is 42,600 mg/L, and the 28-day biodegradation rate is 68.3%. This system can replace traditional sulfonated drilling fluids and provide a green and feasible technical solution for safe and efficient drilling in deep high-temperature formations.