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

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, crude-glycerin-based aqueous mud (CGBAM), when estimating a rock–fluid system's physical properties through electrical and sonic properties (Vp and Vs). 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.