Optimizing Drilling Performance by Wellbore Stability and Pore-Pressure Evaluationin Deepwater Exploration

摘要

This paper discusses the most important drilling hazardsrnrelated to borehole instability and pore pressure in deep waterrnwells. A case study from a deep water well, which hasrnexperienced wellbore stability and loss of circulationrnproblems, especially over intervals with higher angles of holerndeviation, is presented. The answers provided by the studyrnincluded properties, such as, recommended mud-weightsrn(minimum & maximum) as a function of angle of deviation,rnrock strength and computed pore pressure. The determinationrnof rock strength along with the optimum mud-weight windowsrnimproved overall the drilling performance in the next deeprnwater well by minimizing washouts, loss of circulation andrnoptimizing casing design by elimination of unnecessary casingrnstrings. Moreover, improvement of bit performance wasrnachieved by using the predicted rock-strength values. As arnresult, drilling time and well construction costs werernsignificantly reduced.