Trials and Tribulations of a Long-Reach Well in the Deepwater GOM

Abstract

AbstractWhere the water-bottom topography is irregular, sub-sea infrastructure can often be placed in only a few locations above an offshore field. This can constrain access to reservoir targets, particularly when there are drilling challenges above the reservoir, like pressure ramps or layers with unstable lithologies. Given the size of this field, long stepouts are required. This paper presents the strategies implemented to successfully drill and access reservoirs in a large faulted anticline in the deepwater Gulf of Mexico (GOM).The well in question faced three challenges. First, the well would be the longest stepout (~7,400 ft of lateral stepout over ~10,000 ft of vertical depth) drilled to date in the field. Second, the well would target a fault block in a portion of the field that was poorly constrained due to limited offset well control and a poorer-than-normal quality seismic image. Third, the well would face several wellbore integrity challenges in the form of two pressure ramps, an interval prone to borehole instability and one pressure regression.Wellbore integrity management made use of real-time equivalent circulating density (ECD) and bulk-density to optimize drilling, monitor borehole stability and limit formation damage. After drilling to total depth (TD), log formation pressure and imagelog (dipmeter) data would confirm that the well had crossed an unexpected fault in the targeted reservoir section, which caused one of the target reservoirs to be absent. The team quickly reacted to the result, evaluated a recently acquired seismic dataset, updated the structural model, examined the options and successfully drilled a sidetrack.Utilizing long step-out wells, though challenging, is the only viable alternative to access difficult-to-reach deepwater reservoir targets. Improved wellbore placement was achieved at reduced drilling risk based on real-time formation evaluation, informed decisions on optimal drilling parameters, and the continuous evolution of the reservoir model while drilling.