A novel ultra-high-temperature emulsifier stable at 250 ℃ for oil-based drilling fluids: Synthesis, performance, and mechanism

The ultra-high temperature conditions encountered in deep oil and gas exploration represent a critical challenge to oil-based drilling fluid (OBDF) technology. Conventional emulsifiers suffer from rapid deterioration of interfacial stability under harsh environments exceeding 200 ℃, significantly increasing the risk of emulsion breakdown and creating a critical bottleneck for ultra-high temperature drilling operations. To address this challenge, this study aimed to develop a novel high-efficiency ultra-high temperature emulsifier (UHT-EM). The UHT-EM was successfully synthesized via a three-step method, and its molecular structure and excellent thermal stability were confirmed by Fourier-Transform Infrared Spectroscopy (FT-IR) and Thermogravimetric Analysis (TGA). The key synthesis process was optimized using response surface methodology, establishing optimal conditions (molar ratio 1.8, temperature 53 ℃, catalyst dosage 13.4%) with an actual yield of 85.23%. Performance evaluation demonstrated that UHT-EM significantly reduced oil-water interfacial tension. At a dosage of 1.0%, the emulsion maintained optimal rheological properties and electrical stability (ES > 1400 V) after thermal aging at 230 ℃. Systematic temperature resistance tests revealed that the UHT-EM system maintained structural stability at 250 ℃, while experiencing sharp performance deterioration at 260 ℃ due to interfacial film disruption. Microscopic analysis revealed that stabilization mechanism arose from a dense interfacial adsorption layer, while interface failure was caused by intensified molecular thermal motion under high-temperature conditions. The innovation of this research lay in developing a novel emulsifier with well-defined temperature resistance and revealing its stabilization and failure mechanisms through multi-scale analysis, providing crucial material support and theoretical foundation for ultra-high temperature drilling fluid design.