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

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 118705, "Trials and Tribulations of a Long-Reach Well in the Deepwater GOM," by Ron Day, Ramsey Fisher, SPE, and Louise Jacobsen Plutt, SPE, BP plc, and Nesny Pardo, SPE, Segun Jebutu, SPE, and Hans-Christian Freitag, Baker Hughes, prepared for the 2009 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 17-19 March. The paper has not been peer reviewed. For deepwater offshore areas with irregular water-bottom topography, subsea infrastructure above the field often can be limited. Access to reservoir targets becomes constrained, particularly when drilling challenges exist above the reservoir, such as pressure ramps or layers with unstable lithologies. Long stepouts can be required. Strategies implemented to drill and access reservoirs successfully in a large faulted anticline in the deepwater Gulf of Mexico (GOM) are presented. Introduction Discovered in 1998, the subject field is in the Green Canyon protraction area of the GOM in a water depth of 6,800 ft. The main reservoir targets are stacked oil-bearing turbidite sands at a depth of approximately 9,800 ft below the mudline. As shown in Fig. 1, the field is a large faulted anticline 11 miles long by 4 miles wide. Development is complicated by shallow salt fingers that obscure seismic imaging of the north flank of the structure and create a complex water bottom across the middle of the field where water depth changes 2,200 ft across a 1-mile width. Because of this lack of clarity on the northern flank, the south flank of the field was developed first from a central drill center, designated as Drill Center One (DC1). Drilling Challenges Well U was the sixteenth penetration in the field. Like all development wells drilled from DC1, Well U had three strings of casing (36-in. surface casing set approximately 200 ft below mudline; 26-in. conductor casing set at approximately 1,200 ft below mudline; and 20-in. casing set at approximately 2,300 ft below mudline) set during the 2004 batch-set operation. However, Well U, would need to mitigate three main drilling challenges in its remaining 17×20-in., 14 3/4×16 1/2-in., and 12 1/4-in. hole sections. First, Well U would need to navigate through a 1,000-ft-thick laminated and thin-bedded sand, which had caused severe lateral vibrations to the drilling assembly in previous wells, making directional control difficult and occasionally leading to downhole-assembly failures. As a result, vibration management became crucial in drilling the 14 3/4×16 1/2-in. section in one trip. An additional complication in the 14 3/4×16 1/2-in. section was that it would reach total depth in a pressure ramp, which could contribute to borehole instability.