Experimental study on microstructure and rheological behavior of organobentonite/oil-based drilling fluid

In this study, the rheological behavior of drilling fluids consisting of organobentonite/oil was studied. Montmorillonites intercalated with two quaternary ammonium surfactants, hexadecyltrimethylammonium (HDTMA+) and bis (hydrogenated tallow alkyl) dimethyl ammonium, named as HDTMA-MMT and PM199, respectively, were chosen as the rheological control additives in diesel oil. The effect of surfactant type, amount of organobentonite, temperature and pressure was quantified. The microstructures of organobentonites were examined to analyze the gel volume and the rheology of the oil suspension. The XRD results demonstrated that the basal spacing of PM199 increased after the sorption of diesel oil, and the platelets of PM199 exfoliated as the amount of diesel oil increased. The swelling and gel formation of organobentonites in the oil indicated that PM199 had a stronger interaction with the oil molecules compared to HDTMA-MMT, which was also studied and can be related to the surfactant type and initial basal spacing of the organobentonites. It was observed that the viscosity of organobentonite suspensions decreased by increasing the temperature from 25 to 60 °C, followed by increasing viscosity by raising the temperature from 60 to 150 °C. Additionally, the viscosity of the organobentonite suspensions increased as the pressure increased due to the changes in organobentonite-oil pair solvency and oil viscosity. The experimental results suggests that organobentonites with a paraffin-type surfactant arrangement may potentially be used as a potential control additive of organic/oil-based drilling fluids under high temperatures and pressure because of the ease of particle dispersion.