Ultra-High Temperature Suspension Stabilizer HPAS for Oil-Based Drilling and Completion Fluids and Its Working Mechanism

Oil-based drilling and completion fluids presently in use have poor suspension stability at high temperatures up to 240℃ or higher. To deal with this problem, a strongly hydrophobic suspension stabilizer HPAS was developed based on the principle of strengthening the stability of a colloidal system through spatial grid structure. HPAS was synthesized using sepiolite fiber and n-octyltriethoxysilane as the raw materials. The final product was obtained by treating the intermediate product with hydrochloric acid and then organic modification. Characterization of HPAS with IR, TGA, particle size analysis and surface wettability proved that the modification is successful. A high-density oil-based drilling fluid was formulated with HPAS. After aging at 260℃, the properties of the drilling fluid were still good, the AV and PV of the drilling fluid were about 33 mPa·s and 27 mPa·s, respectively, the YP of the drilling fluid was at least 4 Pa, the electric stability was higher than 800 V, the HTHP filter loss was kept under 5 mL, and the thickness of the mud cake was less than 2 mm. Evaluation of the sedimentation stability of the drilling fluid showed that after standing at 240℃ for 7 d there was no hard sedimentation found, and a glass rod can freely drop through the drilling fluid to the bottom of the mud container. Moreover, the YP of the drilling fluid remained at more than 4.5 MPa at temperatures between 65℃ and 240℃ and pressures between atmospheric pressure and 190 MPa, indicating that the drilling fluid can maintain good suspension stability and solids carrying performance under these conditions. The development of this drilling fluid provides a technical support for the use of oil-based drilling and completion fluids in drilling deep, ultra-deep wells and even wells of ten thousand meters in depths.