Well-Integrity Operations at Prudhoe Bay, Alaska

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 102524, "Well-Integrity Operations at Prudhoe Bay, Alaska," by J. Anders, SPE, S. Rossberg, SPE, A. Dube, SPE, H. Engel, SPE, and D. Andrews, SPE, BP Exploration (Alaska) Inc., prepared for the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 24-27 September. Well integrity spans the entire life of the well. The issue of sustained casing pressure (SCP) on the annulus of a well has shaped current well-integrity practices. The well-integrity-management system used at Prudhoe Bay has been evolving since field startup in 1977. Extensive experience has resulted in the design and management of systems to ensure safe operations and compliance with industry standards, regulatory-agency requirements, and internal company policies. The full-length paper details the operational and well-intervention phases of well life and discusses evolution of the well-integrity-management system. Introduction BP Exploration (Alaska) Inc. is operator of the Prudhoe Bay field, on the north slope of Alaska. There are approximately 1,330 wells in the field including 416 gas lift, 591 naturally flowing, and 323 injectors. Wells produce at rates as high as 10,000 BFPD and 100 MMcf/D. Gas-injection wells inject as much as 250 MMcf/D. Tubing sizes vary from 3 1/2 to 7 in. to accommodate the range of rates. Shut-in tubing pressure on naturally flowing wells is 2,400 psi. Produced gas contains 20% CO2, resulting in the extensive use of corrosion-resistant alloys for well tubulars. A 2,000-psi gas lift sys-tem pressure is available, resulting in as much as 2,000-psi shut-in pressure on gas lift wells and the potential for as much as 2,000 psi on well annuli. Fig. 1 illustrates a typical completion. Well integrity is defined in the NORSØK Standard D-010 (developed by the Norwegian petroleum industry) as the "Application of technical, operational, and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well." This is a highly effective definition and has been adopted by BP in Alaska. Well-Integrity-Program Design Well integrity has been an ongoing effort throughout the history of Prudhoe Bay. During the design phase, all potential uses for the well should be considered, including conversion to artificial lift and injection and well-operating and -servicing requirements. Regulatory requirements and industry standards are available to guide the drilling and completion phase, but there are few guidelines for the operation, production, and workover phases. Well-integrity engineering was managed as a component of a production engineer's job responsibilities until the mid-1980s. Because well integrity can present potential conflicts with production delivery contracts, the well-integrity programs were unified under one position, the well-integrity engineer, in 2000. Industry standards, regulatory requirements, company standards, and local events are evaluated and incorporated into the Prudhoe Bay well-integrity system. These are summarized in the Alaska "Well Integrity System Policy." Each operational group, such as drilling, well operations, and the well-integrity team, has further refined these requirements into standard operating procedures (SOPs) used by engineers, operators, and technicians during performance of their job duties.