A Novel Thermo-Thickening Oil-Based Drilling Fluid Based on Composite Thickener Under High Temperature and Pressure

Under high-temperature conditions in deep well formations, oil-based drilling fluids tend to show degraded rheological properties and reduced suspension capacity, which may impair wellbore cleanliness and circulation pump pressure and hinder drilling. To address this issue, a three-component composite thickener including fatty acid polymers and clay activator was developed, and then the composite agents were used as the core component in formulating a thermo-thickening oil-based drilling fluid. Experimental results demonstrated that at up to 200 °C and 153 MPa, the fluid’s low-shear-rate viscosity and yield point increased steadily, while high-shear-rate viscosity and plastic viscosity remained nearly unchanged. The composite thickener largely enhanced the fluid’s storage modulus and inner structural force, thus improving its rheological properties and suspension capacity under high-temperature and high-pressure conditions. Based on these findings, the thermo-thickening oil-based drilling fluid was supposed to address the critical diminished rheological stability and suspension capacity of conventional oil-based drilling fluids in complex formations with promising application prospects.