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

Extended-reach drilling (ERD) offers significant economic and operational advantages but poses severe friction challenges due to complex wellbore geometries and extreme operating conditions. This study investigates the multi-interface lubrication behavior of OBDFs, particularly under high-pressure and high-temperature environments encountered in ERD. A series of laboratory tests were conducted to evaluate the lubrication performance of OBDFs at metal-rock, metal-mud cake, and metal-metal interfaces using specialized apparatus. Lubricants including PF-LUBE OB, PF-LUBE EP, and CX-300 were assessed across varying concentrations, loads, and simulated formations. Results show that at 2 wt% dosage, PF-LUBE EP reduced the metal-rock friction coefficient from 0.01025 to 0.00648 (a 36.8% decrease), metal-mud cake interface from 0.23075 to 0.16726 (−27.5%), and metal-metal from 0.11943 to 0.08058 (−32.5%). A quantitative scoring system standardized against water and base oil was developed to compare overall lubrication efficiency, which PF-LUBE EP scored 155.39 on average (mineral oil = 100). The findings highlight that effective lubricant selection and dosage optimization are critical for ensuring safe and efficient ERD operations, especially in offshore environments. This work provides technical guidance for enhancing drilling fluid formulations to mitigate frictional issues and improve drilling reliability under extreme conditions.