Predicting and Preventing Wellbore Instability: Tullich Field Development, North Sea

Abstract

Summary Innovative geomechanical, drilling, logging, and seismic techniques have been used to successfully develop a geologically complex discovery in the North Sea, Tullich field. With individual reservoir-unit thicknesses below the limit of seismic resolution, and a restricted depth window for completion, optimal placement of horizontal production wells was vital to the successful and economical development of the field. Wellbore instability was a key concern after recent experiences while drilling similar formations in nearby fields. These events had resulted in significant nonproductive time and cost overruns. A geomechanical model was constructed from data acquired during the appraisal-drilling phase and was used to make stability predictions for the proposed horizontal production wells. Wellbore instability while drilling was prevented through the application of a real-time wellbore-stability management system that validated the stability predictions by monitoring surface and downhole drilling parameters, produced solids, fluids, and log data. By combining efficient teamwork and a variety of logging and drilling technologies, the complex reservoir was successfully developed, both in terms of cost savings during well construction and subsequent oil production that exceeded expectation.