Integrated Approach to Drilling Fluid Optimisation for Efficient Shale Instability Management

Abstract

Abstract An integrated approach to drilling fluid design and optimisation, in terms of mud weight and chemistry, for efficient shale instability management has been developed in a collaborative project. The key drilling fluid-shale interaction mechanisms included in the state-of-the-art design criteria are mud pressure penetration, chemical potential and swelling-hydrational stress. Fundamental concepts, processes, models and a range of novel test equipment and procedures for laboratory simulation of the mechanisms were developed. Shale and drilling fluid properties required for the models were determined using a range of analytical and laboratory techniques. The laboratory simulation results for various mud types were used in the refinement and verification of the models. The verified models, which have been integrated in a wellbore stability analysis software, were used to conduct analyses to demonstrate the effects of shale and drilling fluid properties on time-dependent wellbore (in)stability. They highlight the conditions in which the mechanisms are critical and need to be incorporated in the analysis. In addition, the test equipment also provide effective methods of screening drilling fluids (type and formulation) for their capacity to provide the required effective mud support with time for a given shale. The understanding of the mechanisms of drilling fluid-shale interaction and the development of the capacity to model them enabled the development of drilling fluid design charts. These charts, together with a shale property database and property correlations, provide a pragmatic and effective approach for designing optimal drilling fluids to manage shale instability efficiently. The wellbore stability analysis software and drilling fluid design charts have been used in both drilling fluid program recommendation and back-analysis of field experience. A full-scale field trial of the technology is currently being undertaken in collaboration with an operating company.