Impacts of a New Drilling Fluid Invasion on Electrical Resistivity and Acoustic Velocity Measurements

Abstract

When mud filtrate invades a geological formation, it alters its physicochemical characteristics. This invasive process divides the formation into four zones: mud cake, flushed zone, and transitional; immediately after that, there is a virgin area. Each of these zones contains a mixture of fluids: drilling fluids and original formation fluids. Thus, all well-logging measurements are influenced by mud filtrate invasion. The goal of this research was to analyze the effects of a new drilling fluid system invasion, crudeglycerin-based aqueous mud (CGBAM), when estimating a rock− fluid system's physical properties through electrical and sonic properties (V p and V s ). To accomplish this objective, resistivity and transit time laboratory measurements were performed on Berea sandstone samples under dry conditions and brine-and mud filtrate-saturated conditions. According to the results, the invasion of this aforementioned mud filtrate did not affect the characterization of sandstones through sonic properties. Although the crude-glycerin-based aqueous mud has rheological behavior like that of an oil-based mud, it presented unusual behavior from an electrical resistivity and sonic point of view. CGBAM showed sonic properties like the water-based mud and resistive behavior between oil-and water-based muds; therefore, it improves the drilling process and geophysical interpretation regarding the clear distinction between the oil and water zones of the reservoir.