Comparative Evaluation of Sustainable Bio-Oils and Conventional Diesel in Invert Emulsion Muds

Abstract

The global transition toward sustainable drilling practices has intensified the search for biodegradable alternatives to mitigate the environmental risks associated with conventional diesel-based drilling fluids. This study reports a comparative investigation on the use of Castor Seed Oil (CSO) and Palm Kernel Oil (PKO) as environmentally friendly continuous phases in invert emulsion muds. Four different systems were analyzed including a standard diesel oil (Sample A), single source bio-oils (Samples B and C) and a PKO/CSO bio-blend (Sample D). Bio-oils were extracted using the Soxhlet extraction and were formulated as 350 mL laboratory barrel mud systems. Results showed the PKO/CSO bio-blend (Sample D) is an optimized and technically superior alternative to commercial diesel. Physicochemical analysis showed that, although the diesel-based mud had slightly acidic pH values of 6.5, the pH composition of bio-based formulations was neutral with pH equal to 7.0, indicating improved chemical stability, as well as lower corrosion potential. In addition, Sample D produced a good enough density of 8.31 PPG, which can guarantee the proper hydrostatic pressure for normal drilling operations. Rheological testing proved to be a significant synergistic effect in the binary blending of PKO and CSO Sample D reached a Yield Point (YP) of 52 lb/100ft², representing a 48.6% increase over the diesel control (35 lb/100ft²). This led to an Apparent Viscosity (AV) of 71 cP which is almost 2.5 times more viscous than control (29 cP) confirming a stronger emulsion for optimum cuttings transportability. The bio-blend also optimized the Plastic Viscosity (PV) to 33 cP to offer efficient YP/PV ratio of 1.57 and a gel-strength of 4lb/100ft², which ensures reliable cuttings suspension while minimizing breakdown pressures during pump startup. Rheological measurements confirmed that all formulations exhibit pseudoplastic (shear-thinning) behavior. Sample D showed the highest shear stress across all shear rates, indicating the highest structural integrity and dynamic cutting carrying capacity as compared to the other mud samples tested. This study concludes that the PKO/CSO blend effectively bridges the gap between sustainable base oil technology and high performance drilling requirements, offering eco-friendly alternative to conventional drilling base oils.