Key Elements in Ultra-Deep Water Drilling Riser Management

Abstract

Understanding the response of the drilling riser in ultra-deep water is critical for effective riser management and successful drilling operations. Due to the relative shortage of industry experience in ultra-deep water, analysis conducted prior to an operation is a key supplement to judgement and common sense. Damage or loss of the riser or the BOP leads to high costs for riser replacement and rig downtime. The riser can be subjected to various loading configurations during a drilling operation. Storms and/or high current conditions can be encountered while the riser is in the following configurations: deployment; connected and tensioned; subjected to vessel drift-off; subjected to recoil after an emergency disconnect; and suspended in a hang-off condition. The unique aspects of each of these riser loading configurations in ultra-deep water warrant careful attention by riser analysts to provide operations personnel with well-founded guidance and an idea of what to expect in the field. This paper provides an overview of the key elements of drilling riser analysis in ultra-deep waters. Analysis results are presented on the topics listed above, along with operational applications for several ultra-deep water drill ships. Shortcomings and uncertainties in riser analysis are discussed. The results show that analysis of key drilling riser configurations is critical for understanding riser response during operations and effective riser management. Introduction In the past decade, the oil industry has made substantial investments in floating drilling rigs, leases, geological and geophysical work for water depths of 6000 to 10,000 feet. Global Marine, Inc. has been active in new construction and modification of rigs including three drillships. One of these drillships is the Glomar Explorer, which was leased by Global Marine, Inc. from the U. S. Government. The modifications on the Glomar Explorer were completed in 1998, allowing the vessel to drill in water depths up to 7800 feet. Global Marine, Inc. also owns and operates two new-built rigs, the Glomar C. R. Luigs, which is equipped to drill in 9000 feet of water and the Glomar Jack Ryan, which is equipped to drill in 8000 feet of water. The Glomar C. R. Luigs is the subject of analysis to be discussed in this paper. In drilling an ultra-deep water well, key elements of the riser design and operation warrant special attention to ensure the integrity of the riser system. These include:Riser Hang-offDrift-OffRiser Tensioning / Wear AvoidanceVortex-Induced VibrationsRiser CollapseRiser Loading on the BOP, Wellhead, and CasingRiser Recoil The first portion of this paper provides a discussion of analysis procedures and sample results for the first two topics listed above, riser hang-off and drift-off. The sample results for these two topics are based on Glomar C. R. Luigs operations in 8850 feet of water in the Gulf of Mexico. Following this, a brief discussion is given for each of the other five items listed, focusing on key topics of interest for ultra-deep water.

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