Installation of Deepwater Pipelines Utilizing S-Lay Methods
Authors: Gernon G.O. , Kenney T.D. , Harrison G. , Prescott C.N. 
Published: October 2008

Installation of two (2) 54 mile long 12" diameter pipelines for the Enserch GB388 Development spanning water depths from 240 feet to 2340 feet was recently accomplished utilizing a single lay method - S-Lay, and a single lay vessel - McDermott DB28.

To date these are the deepest pipelines installed employing the S-Lay method from a conventional lay barge. These advancements provide the offshore industry are more viable alternative for installation of deepwater pipelines.

This paper describes the background which led to the decision to S-Lay these pipelines, the subsequent challenges faced and some of the innovations implemented in completing this project.

INTRODUCTION

Pipelines in the Gulf of Mexico have been installed by several methods including Lay, S-Lay, Bottom combinations of these. applications depending depths and specific project Tow and various Each method has its on pipe size, water requirements.

Prior to the GB388 Development, some combination of these methods was required for pipelines spanning from relatively shallow water depths (less than 500') to deepwater (greater than 1600'). Developments implemented on the GB388 Project demonstrated the feasibility of utilizing a single lay method for the total range of water depths encountered, thereby saving time andmoney.

Many of the challenges faced during planning and executing this project are discussed herein.

GB388 PIPELINE SYSTEM

Enserch's Garden Banks 388 Development required a pipeline system to gather the production from the deepwater wells in 2100 feet of water, transport it to a platform in relatively shallow water (245 feet) for further processing and metering and then transfer the produced oil and gas to existing pipeline networks for sale.

The system was designed with 2-12" a Gathering Pipelines, one each for oil and gas, from the deepwater drilling/production template to the Shallow Water Facilities. From the Shallow Water Facilities, 1- 12" o Gas Sales Pipeline and 1-8"' a Oil Sales Pipeline would connect to existing trunkline in the same block, A total of 110 miles of pipelines comprised the system, the bulk of which was contained in the two (2) 54 mile long gathering pipelines.

Pipelines in the Gulf of Mexico had been previously installed to water depths similar to those encountered along the Enserch routes, but' never with the same installation method throughout, Conventional S-Lay, a pipelay method in which the pipe is welded in a horizontal position and lowered to the sea floor in a double curve resembling an elongated "S", had long been established as a viable method from shallow water to water depths approaching 1500 feet. (See Chart), J-Lay, the method in which the pipe is welded in a near vertical position and lowered to the sea floor in a configuration similar to a "J", had been introduced very successfully for depths from 600 feet to 10,000 feet and beyond.

However, for the GB388 Pipelines, J-Lay could not be readily utilized for the shallow water portions because of the method's minimum depth requirements and S-Lay had never been attempted for depths encounterednear the deep end of the routes.