Laboratory Study on High Temperature Low Density Oil Base Drilling Fluids

A high temperature low density oil base drilling fluid was formulated with a newly developed organophilic clay MZ to protect low pressure reservoirs in high temperature deep wells. In laboratory experiment, the colloid fraction of MZ was greater than that of another three organophilic clays:A828, B500A and B38. The colloid fraction of MZ in diesel oil can be as high as 97.4%. The properties of the slurry made from MZ only change slightly before and after hot rolling at high temperatures, indicating that high temperature does not destroy the spatial network structure formed by the coalescing and crosslinking of the particles of MZ, and MZ has good colloidal stability and thermal stability. The crystal interlayer spacing of MZ is 2.05 nm. Substitution of quaternary ammonium ions for metal ions in the crystal layers of bentonite increases the crystal interlayer spacing. Testing on the high temperature low density oil base drilling fluid formulated with MZ showed that the viscosity o the drilling fluid changed only slightly before and after hot rolling. After hot rolling, the gel strengths of the drilling fluid increased, and the HTHP filter loss was less than 3 mL. Oil base drilling fluids formulated with MZ are resistant to high temperature to 220℃, contamination from invasion of 50% salt water or 15% shale cuttings, satisfying the needs of drilling deep wells penetrating complex formations.