A Novel Star Polymer based Fluid Loss Control Additive for Non-Aqueous Drilling Fluids

Abstract

Abstract Non-aqueous fluids (NAF) are considered as efficient and reliable drilling fluid systems for challenging wellbore conditions, such as high-temperature drilling operations. NAFs require fluid loss control additives to reduce filtration loss into the formation with minimum filter cake thickness. Polymer developed in this work demonstrated exceptional properties such as high dispersibility, good thermal stability and low plastic viscosity, when compared with traditional natural and synthetic-based fluid loss control additives (e.g., gilsonite). We have utilized a synthetic molecular optimization process to precisely adjust the hydrophilic-lyophilic balance (HLB) by altering the ratio of hydrophilic to hydrophobic monomers. This has allowed us to achieve an HLB that facilitates easy dispersion within NAF formulations. The star polymer was produced using a controlled/radical polymerization technique called Reversible Addition Fragmentation Chain Transfer polymerization (RAFT). The properties of the NAFs, such as rheology, fluid loss, mud cake thickness, and emulsion stability, were evaluated and compared with commercially available fluid loss control additives under simulated downhole pressure and temperature conditions. The chemical structure and thermal stability of the star polymer were analyzed using spectroscopy and thermogravimetric analysis. The spectroscopic studies confirmed the formation of desired polymeric structures and the molecular weight desired. Star-polymer synthesized herein has excellent thermal stability up to 450 °F with great fluid loss control and ultrathin filter cake for NAF systems for mud weight ranging from 10 to 17 lbm/gal. The star polymer also improves emulsion stability. Plastic viscosity (PV) is usually increased with the addition of commercially available fluid loss control additives; however, star-polymer had a negligible effect on PV. Results for both diesel and mineral oil-based mud systems will be presented. High-temperature high-pressure viscometer (Fann 77) was used to study rheological properties at up to 350 °F and 10,000 psi. Our recent work has resulted in the creation of a cutting-edge star polymer (NSP) for use in the industry's next-gen high-performance fluid loss additives. The polymer network can be efficiently synthesized and scaled up for commercial production, providing engineers with an improved solution for drilling high-temperature wells (up to 350°F) with reduced plastic viscosity and increased emulsion stability, while also providing excellent fluid loss control.