The oil-based mud is preferred to drill highly technical and challenging formations due to its superior performance. However, the inadequate chemical and thermal stability of conventional additives have greatly influenced the performance of oil-based mud at high-temperature conditions. Therefore, it is critical to design an oil-based mud with additives that withstand and improve its performance at high-temperature conditions. The nanoparticles have emerged as an alternative to the conventional additives that can significantly enhance the rheological and filtration characteristics of oil-based mud at high-temperature conditions. In this research study, a novel formulation of OBM enhanced with GNP is formulated, and its performance at high-temperature conditions is investigated. An extensive experimental study has been performed to study the effect of graphene nanoplatelets on the rheological and filtration properties along with flow behaviour, viscoelastic properties, electrical stability and barite sagging of oil-based mud at high temperatures. The graphene nanoplatelets are characterised to ascertain their purity and morphology. The result shows that the graphene nanoplatelets exhibited efficient performance and improved the rheological and filtration properties of oil-based mud. The plastic viscosity and yield point are improved by 11% and 42%, with a concentration of 0.3 ppb. Similarly, the gel strength and barite sagging tendency are enhanced by 14% and 2%, respectively. The filtration loss is also significantly decreased by up to 62% and 46%, with 0.5 ppb concentration at 100 and 120 °C. The addition of GNP results in the formation of a thin mud cake compared to the base mud sample. The rheological modelling recommends the shear-thinning behaviour of oil-based mud (n < 1), which is correlated with the Herschel–Bulkley model. An Artificial Neural Network model is developed to predict the viscosity of OBM based on the four input parameters (concentration of nanoparticles, temperature, shear rate and shear stress). The results demonstrate that graphene nanoplatelets have a favourable impact on the performance of oil-based mud. The addition of graphene nanoplatelets, even at small concatenation, has significantly improved the properties of oil-based mud at high-temperature.Graphical abstract

This study focuses on developing an efficient and environment-friendly drilling fluid using biodiesel as an alternative to the conventional diesel-based drilling fluid for drilling highly technical and challenging formations. The biodiesel was synthesized and produced from castor oil using the transesterification process. The physicochemical properties suggests that produced biodiesel has a high flashpoint (148 °C) and low pour point (-12 °C) compared to diesel oil. The synthesized biodiesel is utilized as a base oil to formulate an ester-based drilling fluid. A thorough experimental study is performed to evaluate the performance of formulated drilling fluid at ambient and reservoir temperature condition. A diesel-based drilling fluid is also formulated for comparative analysis. The experimental findings show that castor biodiesel-based drilling fluid's plastic viscosity and yield points are 10% and 25% higher than the diesel-based drilling fluid. However, the least filtrate loss volume is obtained for castor biodiesel-based drilling fluid than the diesel-based drilling fluid at high-temperature conditions. The filtrate loss by diesel-based drilling fluid was 17% and 9% higher than castor biodiesel-based drilling fluid at 25 °C and 100 °C, respectively. The results suggest the non-Newtonian and shear-thinning behavior of castor biodiesel-based mud (n < 1) associated with the Herschel–Bulkley model.