Evaluation of a soybean oil derived surfactant in the development of oil-in-water (O/W) emulsion drilling mud for shale formation

Abstract

Drilling fluids having a few ecological footprints are extremely desirable, particularly for drilling in the highly complex shale formation zone. In the current work, an anionic surfactant was synthesized in the laboratory using soybean oil and characterized based on Fourier transform infrared spectroscopy (FT-IR), thermal gravimetry analysis (TGA), and critical micelle concentration (CMC) value. The synthesized surfactant was used to formulate and stabilize environmentally-friendly oil-in-water (O/W) emulsion drilling muds, having soybean oil itself as a dispersed phase, for drilling shale formation. A comparative study on the rheological and filtration properties of soybean oil based emulsion mud systems and a conventional diesel oil based emulsion mud system, prepared in the presence of the synthesized surfactant, was also performed. The properties of soybean oil based emulsion mud systems were found to be superior to diesel oil based emulsion mud. The effect of varying oil content and mud additives (i.e., gum acacia or xanthan gum, and bentonite) on the rheological and filtration properties of drilling mud was also investigated in detail in order to achieve an optimum formulation. Considering the high-temperature application, the thermal stability of rheological and filtration properties of developed muds was investigated up to a temperature of 125 °C, and muds were found to be having excellent thermal stability. The developed emulsion mud systems were also found to be showing an excellent tolerance towards mud constituents like salt (KCL). The lubricity of the mud was evaluated, and it appeared that the soyabean oil based mud possesses an excellent lubricity compared to that of diesel oil based mud. The lubricity of the mud increases significantly with the increase in oil concentration. The shale recovery test and core flooding study, respectively, suggested a high shale recovery performance and low formation damage effect for the developed soybean oil-in-water emulsion mud system. The flow curve of developed emulsion muds depicted the excellent shear-thinning behavior, which is a desirable feature in drilling mud. The mud formulated with a composition of 80 vol% water, 20 vol% soybean oil, 0.3 wt% PAC-LVG, 0.4 wt% synthesized surfactant, 2.5 wt% bentonite, and 0.3 wt% gum acacia was found to be behaving as a Cross-model fluid.