Fluid Loss Control by a Novel Star Polymer for Oil Based Mud

Abstract Non-Aqueous Fluids (NAF) are widely recognized as efficient and reliable drilling fluid systems for challenging wellbore conditions, particularly in high-temperature drilling operations. To minimize filtrate invasion and maintain a thin filter cake, NAFs require effective fluid loss control additives. The polymer developed in this study exhibits superior properties—including high dispersibility, excellent thermal stability, and minimal impact on plastic viscosity—when compared with conventional natural and synthetic fluid loss control additives such as asphaltite. A synthetic molecular optimization approach was employed to fine-tune the hydrophilic-lipophilic balance (HLB) by adjusting the ratio of hydrophilic to hydrophobic monomers. This allowed us to achieve an optimal HLB that promotes easy dispersion within NAF formulations. The star polymer was synthesized using a controlled radical polymerization method, specifically Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization. Key fluid properties—such as rheology, fluid loss, filter cake thickness, and emulsion stability—were evaluated in NAF systems and benchmarked against commercially available fluid loss additives under simulated downhole pressure and temperature conditions. The polymer's chemical structure and thermal stability were confirmed using spectroscopic techniques and thermogravimetric analysis (TGA). Spectroscopic analysis verified the successful synthesis of the target polymer architecture and molecular weight. The resulting star polymer demonstrated excellent thermal stability up to 450°F, along with superior fluid loss control and formation of an ultra-thin filter cake across mud weights ranging from 10 to 17 ppg. Additionally, the polymer significantly enhanced emulsion stability. While traditional fluid loss control additives tend to increase plastic viscosity, the star polymer showed negligible impact on PV. Performance results are presented for both diesel- and mineral oil-based mud systems. Rheological properties were evaluated using a high-temperature, high-pressure viscometer (Fann 77) at temperatures up to 450°F and pressures up to 10,000 psi. This work has resulted in the development of a novel star polymer, representing a next-generation high-performance fluid loss additive for the drilling industry. The polymeric network can be readily synthesized and scaled up for commercial production. The availability of this advanced material will enhance drilling efficiency in high-temperature (up to 450°F) wells by reducing plastic viscosity, improving emulsion stability, and providing superior fluid loss control.