Developing an efficient ester-based drilling fluid based on Calophyllum Inophyllum oil for eco-friendly drilling of unconventional shale formation

The ester-based drilling fluids has been emerged as an alternative to diesel and mineral oil-based drilling fluids and are preferred due to their high biodegradability and low toxicity. In this research study, a novel environment-friendly ester-based drilling fluid has been developed from non-edible vegetable oil. The crude oil extracted from Calophyllum inophyllum seed is transformed into Calophyllum inophyllum methyl ester through two-step esterification and transesterification processes. The physiochemical results suggest the successful synthesis of methyl ester having significantly low kinematic viscosity and higher flashpoint. The Calophyllum inophyllum methyl ester is used as a continuous phase for the formulation of ester-based drilling fluid. A comprehensive experimental study is carried out to evaluate the performance of formulated ester-based drilling fluid at ambient and reservoir conditions. The drilling fluid is examined for its rheological behaviour, filtration characteristic, electrical stability, and viscoelastic properties. The formulated drilling fluid display efficient performance with improved rheological characteristics, reduced filtration loss, high emulsion stability, and enhanced viscoelastic properties. The drilling fluid also performs well at high-temperature conditions and meets the API requirements. The flow behaviour and rheological modelling of drilling fluid are investigated at varying temperatures (25�100 °C) and shear rates (0.1�1200 s�1). The obtained results affirm the non-Newtonian and shear-thinning behaviour of the drilling fluid. The shear-thinning behaviour is quantified using the Herschel�Bulkley model. Oil-based drilling fluid is formulated and tested for comparison. The ester-based drilling fluid exhibit satisfactory rheological characteristics with better filtration and emulsion stability compared to the oil-based drilling fluid. The results exhibit that the formulated drilling fluid can be a viable technical and environmental alternative to diesel and mineral oil-based drilling fluids. © 2022 Elsevier B.V.