Installation of a DP System and Adaptation of the Reel Barge Chickasaw for Deep Water Pipelay

Abstract

ABSTRACT Recently enhanced to permit pipelaying operations in water depths much greater than 1000 ft., the reel barge Chickasaw is now installing deep water pipelines in the Gulf of Mexico. Included in the modifications performed on the barge are the design and installation of a full function, dynamic positioning (DP) system specifically adapted for offshore pipelay. The capabilities and operational requirements of this new system are signit7cantly different from the station keeping of drilling vessels and other traditional DP applications. A fixed, short radius stinger has also been constructed to provide the high, near vertical departure angles required in deep water. The pipe reel has been strengthened and its tension capacity more than doubled to support the increased weight of the pipe column at these depths. As offshore resources are discovered in increasingly deeper waters in the Gulf of Mexico and elsewhere, the capabilities of existing pipelay vessels are being exceeded. The offshore pipeline industry is faced with the need to improve the operating capabilities of existing vessels or undertake the construction of new vessels specifically designed for operation in very deep water. The barge conversion described hereinafter extends the Chickasaw's operating range and ability to lay small to medium diameter pipelines and perform vertical stab-in connections in water depths to 5000 ft. and beyond. The paper describes practical, cost effective modifications which greatly increase the deep water pipelay and operational capabilities of an existing reel vessel. Programs of this type can improve the industry's ability to use offshore resources in very deep waters. INTRODUCTION A number of significant new oil and gas fields have recently been discovered in the Gulf of Mexico in water depths greater than 1000 ft. Many of these fields will be developed using floating production platforms or subsea wellhead production facilities that are tied back to fixed platforms on the continental sheIf or slope by small to medium diameter flowlines. There is an immediate need for pipelay vessels capable of installing these pipelines efficiently in deep water. The ability to install these flowlines at a low cost is critical because, in many cases, the cost of constructing these lines can determine the economic viability of offshore fields in deep water. Pipelay vessels which lay pipe using the reel method are especially well suited for laying small to medium diameter pipelines at low cost. This paper describes a series of changes and enhancements that have been made to an existing reel barge, the Chickasaw, to adapt it for pipelay operations in deep water. CHICKASAW OVERVIEW The Chickasaw is a pipelay barge that installs pipelines using the reel method. It has been in service for more than twenty years. Originally built by Fluor Ocean Services for the purpose of laying small to medium diameter flowlines in the Gulf of Mexico, it has been one of the most productive pipelay vessels in the world. The Chickasaw was designed to operate in water depths up to 1000 ft., but until recently was primarily used in much shallower depths.