High Temperature High Density Drilling Fluid Technology for Yinggehai Basin

Reservoir formations in Yinggehai Basin are of high temperature (186-218℃) and high pressure (coefficient of formation pressure:1.6-2.4). Failure to maintain stable properties of the drilling fluids currently used at high temperature leads to high viscosity which in turn makes weighting of the drilling fluids very difficult. Poor performance of the drilling fluids also caused damage to reservoirs. Optimization has been done to the drilling fluids recently based on the understanding of the formation geology and analysis of the mechanism of formation damage. Ultra-fine calcium carbonate powder and a broad spectrum oil-film temporary sealing agent were added to form high-quality mud cake and tough thin-film. Surfactants were used to improve the surface properties of formation rocks, in an effort to prevent water block from happening. White oil, together with the surfactants, contributes to the temperature stability of the drilling fluids. The optimized formulation remains stable at 200℃ and 2.2 g/cm³, satisfying the needs for drilling operation. Cores flooded with this drilling fluid have permeability return of 90%. It is also resistant to CO₂ contamination.