Stability of Diesel-Oil-Based Drilling Fluid with Variable Water Cut at Low Temperatures

Diesel-oil-based drilling fluid is an oil—water emulsion used in petroleum drilling to change the formation parameters. In this paper, the rheological dispersion, and electric properties of the drilling fluid under water-cut conditions were studied as functions of the oil – water ratio. The experimental results showed that the emulsion stability depended directly on its oil—water ratio and temperature. The apparent viscosity and shear stress increased as the oil – water ration and temperature decreased. The apparent viscosity decreased with increasing shear stress at constant temperature and oil–water ratio. The diesel-oil emulsion acted as a Newtonian fluid at high oil—water ratios but demonstrated properties of a pseudo-plastic fluid at low ratios. The rheological stability continued to decline as the oil—water ratio decreased so that the emulsion was no longer suitable for use as a drilling fluid.