Analysis of the stability of oil-based drilling muds by electrical stability measurements as a function of oil-water ratio, weighting material and lubricant concentrations

Abstract

Oil-based muds (OBM) used in drilling processes are complex fluids formed by a water-in-oil emulsion stabilized by emulsifiers. Measurements of the electrical stability (ES) are considered directly indicators of mud stability, together with yield point (YP), and fluid loss (FL). In this work, it was studied the effect of oil-water ratio (OWR) in the mud stability using the ES, YP and FL data. To analyze those individuals and paired effects, it was applied a Central Composite Rotational Design (CCRD) planning with three replicates at the central point plus eight and six factorial and axial points. Results showed that all studied factors presented a high influence on the ES results. Additional measurements of rheological properties and fluid loss were carried out to verify and analyze the impact of the composition on the main drilling mud properties. Statistical analysis was also performed to clarify the role of the different factors investigated in this research. The authors observed that several drilling mud compositions are not suitable for the oilfield application, and, by an optimization procedure, an optimal formulation has been proposed.