Characteristics of Ultra-Deepwater Pipelay Analysis
Authors: Choi H.S. , Jo H.J. 
Published: October 2008

Several pipelines in water depth greater than 3000 ft are planned to be installed in the Gulf of Mexico. Because of the water depth and diameter of the pipelines, many challenges arise and sometimes no existing vessels can lay the pipelines without major upgrading or modification. In addition, the technical concept of installation is much different from the existing installation techniques. Because of the new challenges of installation of the pipelines in deepwater, the knowledge of installation capacity for laying a particular pipe size is critical factors when planning offshore pipeline projects. The trend of early involvement of operators in installation analysis is more important in deepwater projects to remove any potential risks. During the many installation analysis of deepwater pipelines, the unique aspects arising from the deepwater were found and their characteristics were identified. These new technical aspects are discussed to compare with the conventional shallow water technique. This paper will cover the J-lay installation, abandoning & recovery method, maximum installation bending strain, the possibility of pipe buckling due to power loss during installation, steel catenary riser installation, and fatigue damage of pipe during installation. The main goal of this paper is to identify the new technical problems for the J-lay installation in deepwater. The results of this study will provide better ideas for the future deepwater pipelay analyses and vessel upgrading or modifications.

Introduction

As more offshore pipelines are installed in increasingly deepwater, many specialized design and installation problems have to be solved to meet the new challenges. Today, deepwater generally means more than 1000 ft and ultradeepwater means 3000 ft or deeper for offshore pipeline installation. It is apparent that deepwater pipeline installations receive unprecedented attention.1,2 Some examples of deepwater pipelines are: TransMediterranean pipeline in the water depth of 2000 ft,3,4 Auger pipeline connecting to the tension leg platform (TLP) in the Gulf of Mexico in water depth of 2860 ft, Mars pipelines in water depth of 2940 ft and Ram Powell pipelines in water depth of 3220 ft. The Auger and Mars pipelines were laid with a J-lay system developed by McDermott International.5,6 A 10-inch diameter pipeline installed offshore Brazil in water depth of 4500 ft. The deepest rigid pipeline laid to date is in water depth of 5300 ft in the Gulf of Mexico, but the water depth record will not last long. Three 24-inch pipelines are planned to be installed in 7000 ft water depth in Black Sea. Even though the Oman India Gas Pipeline (OIGP) project was withdrawn, the installation analysis provided valuable information for future deepwater pipelines. Two 24-inch internal diameter gas pipelines with a distance of 1140 km and a maximum water depth is 11,500 ft were planned to be installed from Oman to India across the Arabian Sea.

In the Gulf of Mexico, several pipelines are planned to be installed in ultra-deepwater. These ultra-deepwater pipelines must be designed such that they maintain structural integrity during the installation and operational lifetime. Some of these pipelines are designed as pipe-in-pipe systems to prevent hydrate and wax problem due to the cold water temperature in deepwater. Because of the diameter of the pipe and water depth, the J-lay method is suggested for installation.

The objective of this paper is to discuss the new technical problems of ultra-deepwater pipelines from installation analyses of Auger, Mars, and OIGP pipelines. The installation analyses will provide preliminary data for the feasibility of installation and for the