Drilling experience in K-shale in the Malay Basin (South China Sea, Malaysia) highlighted the issue of wellbore stability in the formation. A wide range of drilling problems has been experienced, ranging from tight hole to stuck pipe. Subsequently, a collaborative project between CSIRO Petroleum and Petronas Research & Scientific Services Sdn Bhd was conducted to address the problems. The aim is to develop a technical framework of drilling fluid design and consolidated into a methodology for overcoming wellbore instability-related problems in the shale.

This paper describes the outline of the project and the approach adopted in the development of the methodology. The approach is based on drilling fluid-shale interaction and proven rock mechanics principles. Based on the gathered drilling experience and laboratory tests conducted on downhole core material, dominant failure mechanisms of the shale were identified. Examples of critical mud weight contour plots and design charts of pressure change (due to drilling fluid-shale interaction mechanisms) which form part of the consolidated methodology for designing optimal drilling fluid are presented. The methodology provides a pragmatic approach for managing shale instability problems in drilling extended reach wells in the Malay Basin as well as other regions worldwide. The approach would result in an increase in drilling efficiency and a reduction in drilling cost.

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