Evaluation and Optimization of Multi-Interface Lubrication Performance of Oil-Based Drilling Fluids for Extended-Reach Wells

Extended-reach drilling (ERD) offers substantial economic and operational benefits by accessing extensive reservoir sections with fewer surface facilities, yet poses significant frictional challenges due to complex wellbore geometries and extreme operating conditions. This study introduces a multi-interface lubrication evaluation framework. It systematically assesses oil-based drilling fluids (OBDFs) across three downhole contact scenarios: metal–rock, metal–mud cake, and metal–metal interfaces under HTHP conditions. We developed a quantitative, normalized scoring system. Benchmarked against distilled water (score 0) and W1-110 mineral oil (score 100), it integrates frictional data from various tests into a unified metric for lubricant comparison. Three candidate lubricants—PF-LUBE EP, PF-LUBE OB, and CX-300—were evaluated at varying dosages, lithologies, and applied loads. Results show that at 2 wt%, PF-LUBE EP achieved the most consistent performance, reducing friction coefficients by 36.8% (metal–rock), 27.5% (metal–mud cake), and 32.5% (metal–metal), with a normalized average score of 155.39, outperforming PF-LUBE OB and CX-300 by 12.5% and 18.3%, respectively. Its superior performance is attributed to a bionic dual-layer film formed by organophosphorus anchoring and alkyl slip layers, enabling self-healing and stability under cyclic loading and HTHP environments. PF-LUBE OB and CX-300 also demonstrated friction reduction but with lower normalized scores (138.06 and 131.27), reflecting less stability across varied conditions. The proposed framework bridges the gap between laboratory testing and field-scale application by capturing multi-interface behaviors, enabling objective lubricant selection and dosage optimization for complex ERD operations. These findings not only validate PF-LUBE EP as a robust additive but also establish a scalable methodology for the development and optimization of next-generation OBDF formulations aimed at reducing torque, drag, and equipment wear in challenging drilling environments.