Mardi Gras Deepwater Pipeline Repair System
Authors: Martin Rob , Killeen Joseph , Chandler Bruce 
Published: October 2008

BP has developed and tested a deepwater Pipeline Repair System (PRS) for the Mardi Gras Transportation System (MGTS). The PRS is unique by virtue of the combination of extreme MGTS parameters such as water depth, pipeline sizes, pipeline pressures, pipeline expansions and soil conditions.

The performance requirements of many of the components of the deepwater PRS, including the multi-diameter Grip and Seal Hydraulic Connectors \ Pipeline Recovery Tools (GSHC\PRT), the Collet Connectors, the Gantry Sleds, the Pipe Lift Frames (PLF) and the Vertical Jumper Spools (VJS) exceed the previous industry benchmarks. As a result, these components required extensive design and manufacturing effort.

This paper describes the pipeline damage scenarios, the corresponding repair methods and procedures, the repair equipment and the associated engineering analysis.

Introduction

BP and its partners are developing several deepwater prospects in the Gulf of Mexico. These include the Holstein, Mad Dog, Thunder Horse, Na Kika and Atlantis floating production facilities in water depths ranging from 4500 feet to 7300 feet. Oil and gas will be exported via the deepwater segments of the MGTS, consisting of 485 miles (this includes the portion of the Okeanos Gas Gathering System laid by Shell Pipeline Co. LP) of pipelines and steel catenary risers (SCRs) with diameters ranging from 16-inch to 28-inch. The schematic layouts of the deepwater portions of the MGTS in the Southern Green Canyon and the Mississippi Canyon regions are shown in Figures 1 and 2 respectively.

The environmental and financial implications of damage to the MGTS led BP and its partners to develop and test a deepwater diverless PRS. The PRS is a modular system that offers the flexibility necessary to adapt to several unique types of repair, including:Minor damage (e.g. pinhole leak) that can be repaired with a clampMajor damage (e.g. buckle) that requires a section of pipeline to be replaced with a spoolCatastrophic damage (e.g. slope failure) requiring a new pipeline to be laid. A detailed investigation and review of the existing pipeline repair techniques and equipment was performed. The decision to use a Vertical Jumper Spool (VJS) arrangement was driven largely by the available synergies with the MGTS "lateral tiein systems" and the accompanying VJS equipment and experience. The PRS was then developed around the VJS arrangement.

Methods and Procedures

The PRS was developed to provide for three repair methods: the Clamp Repair, the Surface-Lift Repair and the On-Bottom Repair. These methods together provide a repair solution for both minor and major pipeline damage. Minor damage is here defined as localized damage that extends over a length of pipe equal to or less than one pipe diameter. Major damage refers to damage greater than one pipe diameter. A repair method selection matrix, Table 1, outlines damage types, limiting parameters and associated repair methods.

Methods.

Minor damage such as a leak may only require a Clamp Repair. A Clamp Repair can be used to repair damage that is both less than one pipe diameter in length and not structurally compromising. Major damage requiring a VJS repair can be accommodated with a Surface-Lift Repair, an On-Bottom Repair, or a combination of both. Major damage ranges from a short buckle to large-scale damage.