Setting the Bear Free: Challenges of the Deepwater Ursa A-10 ERD Well

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 163525, ’Setting Free the Bear: The Challenges and Lessons of the Ursa A-10 Deepwater ERD Well,’ by John Gradishar, SPE, and Gustavo Ugueto, SPE, Shell Upstream Americas, and Eric van Oort, University of Texas at Austin (formerly with Shell Upstream Americas), prepared for the 2013 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 5-7 March. The paper has not been peer reviewed. This case history presents the highly challenging extended-reach deepwater well, Ursa A-10, drilled in the Ursa (Latin for bear) prospect in the US Gulf of Mexico (GOM). This 30,000-ft well, drilled from the Ursa tension-leg platform (TLP) to a vertical depth of 18,000 ft and a horizontal displacement (HD) of 20,000 ft, targeted the Yellow sand in the Ursa/Princess section of the greater Mars-Ursa basin. During drilling of the original hole, a subsequent sidetrack, and two mechanical bypasses, several significant hole problems materialized that led to extensive nonproductive time. At least five independent borehole-failure mechanisms were encountered. Introduction In the aftermath of the tragic 2010 Macondo/Deepwater Horizon event, it is important that the industry share case studies on successful wells. It also is important to share information on wells that proved to be very challenging. Sharing learnings, best practices, and experiences on such wells will raise the overall level of proficiency in constructing these wells throughout the industry. As is often the case, more is learned from adversity than from outright success. This is the main reason that the Ursa A-10 case is presented. Over the last decade, world-class extended-reach-drilling (ERD) wells have been drilled in the continued development of the Mars-Ursa basin in the GOM. These high-deviation wells are distinguished by depth [true vertical depth (TVD) greater than 17,000 ft], HD greater than equal to ;20,000 ft, and overall measured depth (MD) greater than equal to 30,000 ft. Challenges include a geopressured deepwater environment, complex casing programs, and special drilling issues. The combination of these challenges makes the Ursa A-10 case noteworthy. ERD wells have been drilled to longer HD and overall MD, but those wells generally had simpler casing programs and a more-forgiving pore-pressure/fracture-gradient environment with associated drilling margins. Larger margins leave more room for such things as equivalent-circulating-density (ECD) and annular-pressure fluctuations, mud problems (such as barite sag and hole-cleaning and associated pack-off problems), accommodating manageable levels of borehole instability, and implementation of limited redesign philosophies.