A Pragmatic Approach to Managing Wellbore Instability in Extended Reach Wells in the Goodwyn Field

Abstract

Abstract Drilling experience with numerous inclined wells highlighted the issue of wellbore stability in the Goodwyn Field, North West Shelf of Australia. Subsequently, a study, with an emphasis on the longest horizontal well drilled in Australia at that time, GWA 12, was conducted. The aim of the study was to develop strategies to control shale instability during the drilling of future wells in the field. Following the drilling of a number of extended reach wells, a post-drilling review of the wells, including GWA 12, was conducted and the additional information used to revise the critical mud weight contour plots for future application. An assessment was also made of the drilling fluid design for long term stability of GWA 13ST2 based on pore pressure changes induced by key drilling fluid-shale interaction mechanisms. This paper describes the required information, methods used to carry out the wellbore stability analyses and utilisation of the results from the two studies to develop the recommendations for the mud weight programs of the field. The approach adopted in the studies utilises the relevant field observations in vertical and inclined wells to develop strategies to control instability through theoretical wellbore stability analyses. Reference mud weights, based on drilling experience and wellbore condition in the wells, were used to calibrate the predicted critical mud weights. In addition, design charts of pore pressure change due to mud pressure penetration and chemical potential mechanisms were used to assess the drilling fluid chemistry for long term wellbore stability.