Hydrophobic association copolymer as viscosifier for high-temperature high-pressure anti-sedimentation performance of water-based drilling fluid

In this study, a new type of amphiphilic copolymer SPXFJ, with amide and sulfonate functional groups, was synthesized via the free radical polymerization method. And the chemical structure and properties of this new polymer were characterized by elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), intrinsic viscosity tests, and thermogravimetric analysis (TGA). The hydrophobic association and thermo-thickening properties of SPXFJ copolymer were investigated through viscometer, contact angle tester, high-resolution scanning electron microscope analysis, and X-ray laser static scattering (XLSS) test. The test results indicated that SPXFJ copolymer showed superior amphiphilic properties, especially in the solution condition. Furthermore, a thermo-associative behavior was found in the solution that aged at 180°C. Thus, SPXFJ-based drilling fluid showed a higher temperature resistance. The test results, in both high-temperature aging tests and high-temperature high-pressure (HTHP) downhole simulation tests, showed that the water-based drilling fluid showed excellent anti-sedimentation properties with the use of SPXFJ polymer and can be improved significantly, especially in the high-pressure condition. The water-based drilling fluid of 2.0 g/cm³ showed no sedimentation of barite powders at 180°C/100 MPa, of which the density deviation just reached approximately 0.06 g/cm³.