Mineral oil-based drilling muds are toxic, not readily biodegradable and thus have cumulative impact on terrestrial, coastal and marine habitats. The base fluid for mineral oil-based mud development has limited source of supply. Vegetable oils are renewable, highly biodegradable, can be produced as per industry demand and thus could be a suitable candidate for development of a highly biodegradable oil-based mud with a sustainable source of supply. They have higher flash and fire points, better thermal stability, no detrimental impact on the surrounding environment and are much less hazardous compared to mineral oils. Due to biodegradable nature of vegetable oils, drill cuttings will have no environmental impact if the cuttings are disposed directly to the surrounding environments. Due to non-reactive nature of vegetable oils with clays and shales, their technical performance in maintaining borehole stability is comparable to mineral oil. On the other hand, due to readily biodegradable nature and negligible toxicity effect, vegetable oil-based mud performance should be comparable to water-based mud from environmental point of view. Hence, vegetable oil-based mud could be a potential solution to meet the current as well as future technical and environmental challenges.

An invert emulsion mud was developed using a blend of vegetable oil to study the rheological and filtration properties and evaluate its suitability for oil well drilling. Initial mud formulation indicates that development of a viable OBM is not possible using the conventional approach due to the high inherent viscosity of vegetable oils and significant thermal degradation at high temperature. However, processing and treatment of vegetable oils lead to the formulation of a vegetable oil-based mud with desirable rheological properties and excellent thermal stability. Preliminary test results indicate that the processed vegetable oil-based mud produces suitable low end rheological properties including gelling characteristics. Thermal conditioning of the mud at 150 °C for 16 hours indicates no significant changes in the rheological properties of the mud. The high thermal characteristics of vegetable oils indicate their safe operation for all practical range of temperatures.

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