Clay-Free High Performance Water-Based Drilling Fluid for Extreme High Temperature Wells

Abstract

Abstract Growing demands to operate in harsh high temperature environments require robust drilling fluid performance to drill in such conditions. Water-based drilling fluids offer significant environmental advantages compared to invert-emulsion fluids (IEFs). High performance (HP) water-based drilling fluids are particularly advantageous compared to conventional water-based systems because they offer faster rates of penetration (ROPs), enhanced hole cleaning and shale inhibition, and improved wellbore stability. Most HP water-based drilling fluids can only tolerate operating temperatures up to 300°F attributed to a strong dependence on biopolymer-based viscosifiers. Thus, deeper exploration in extreme high temperature reservoirs (>300°F) requires new drilling fluid technologies. A new high performance, high temperature water-based drilling fluid that is thermally stable at 400°F has been developed to meet these demands. The new fluid system was fully formulated using a multimixer, and the resulting fluids were hot rolled at 150°F for 16 hours to condition the fluid before testing. The conditioned fluids were then further subjected to dynamic or static aging conditions with temperatures ranging from 300 to 400°F. The aged fluid viscosity was examined using a direct-indicating viscometer, and the pH was determined with a pH meter. The fluid loss properties of the fluids were determined by both API filtration and high-pressure/high-temperature (HP/HT) filtration at 350°F in according with the API recommended practice. This paper presents the detailed study of the high performance, high temperature water-based drilling fluid formulated with 10.0-17.0 lbm/gal densities. The fluid exhibits a stable rheological profile. For example, a 14.0 lbm/gal formulation aged at 150°F for 16 hours yielded a plastic viscosity of 29 cp and a yield point of 22 lbm/100 ft2. After static aging for 48 hours at 400°F, the fluid gave a plastic viscosity of 27 cp and yield point of 24 lbm/100 ft2. The new fluid maintains stable viscosity, adequate suspension, low shear strength, shale stability, and filtration control up to 400°F. This thermally stable, clay-free system exhibits good shale inhibition and is environmentally acceptable for both land and offshore drilling. This HP water-based drilling fluid is formulated with a novel synthetic polymer viscosifier and filtration control agent, allowing removal of thermally labile biopolymers without the addition of clay-based viscosifiers. The new formulation provides reliable thermal stability that can readily function in extreme high temperature wells, while preserving the benefits of HP water-based drilling fluids.