ADS Support for Hardy Oil's Subsea Projects: Simple and Cost Effective
Authors: German Norb , McCullough Gary , Subik Dan 
Published: October 2008

The use of Atmospheric Diving Systems in support of the Shasta and Mustique Subsea Field Developments for Hardy Oil & Gas and Texaco is reviewed as a simple and cost-effective solution to the subsea intervention requirements of underwater completion tiebacks.

The design and installation of the pull-tube system for dual flowlines and a control umbilical on Texaco's Green Canyon 6A Platform is reviewed as an example of how Atmospheric Diving Systems can be utilized to perform the difficult subsea construction of a pull-tube system on an existing deepwater platform.

The design and installation of the flexible flowline jumpers and umbilical flying leads connecting the three subsea trees to the flowline termination skids and the umbilical termination assemblies is reviewed as an example of how Atmospheric Diving Systems can be utilized to connect flowlines and control umbilicals to subsea trees with standard bolted flanged connections and flying leads using the well completion drill rig as a work platform.

Introduction

An Atmospheric Diving System (ADS) is a means of underwater intervention which contains it's diver/operator(s) inside a hard shell that protects them from the pressurized environment and maintains them at the surface pressure, or 'one atmosphere', thereby avoiding the requirement for time-consuming and expensive compression and decompression. The DUAL WASP Atmospheric Diving Systems operated by Oceaneering International and used to support the Shasta and Mustique field developments are one-man submarines rated to 2300 fsw with a 360-degree hemispherical observation dome, fully articulated, fluid-supported flexible arms with direct acting manipulators and four electrical thrusters for maneuvering (see Figure 1).

The Shasta and Mustique subsea field developments are located in the Gulf of Mexico. Shasta well #6 and well #7 are located in Green Canyon 136 in -860 fsw and -I 040 fsw, respectively, and are tied back to Texaco's Green Canyon 6APlatform in 620 fsw by two 4' flowlines and an electrohydraulic control umbilical. Mustique well #3 is located inGarden Banks 240 in -832 fsw and is tied back to Chevron's Garden Banks 236 Platform by two 3' flowlines and an electrohydraulic control umbilical. Pull-tubes were available on the Chevron GB-236 Platform, but either risers or pull-tubes had to be designed, fabricated, and installed on the Texaco Green Canyon 6A Platform. A 16' J-Tube and a 12' I-Tube were installed cmthe GC-6A Platform by WASP Atmospheric Diving Systems working from a four-point moored diving support vessel. The flowlines were connected to the subsea trees by flexible flowline jumpers with conventional bolted flanges, and the electro-hydraulic control umbilicals were connected by flying leads to the subsea trees by WASP Atmospheric Diving Systems working from the well completion drill rig.

Design Requirements

Pull-Tube System.

For the flowline riser installation at the Green Canyon 6A Platform, both conventional riser systems and installation through a retrofitted J-Tube were considered.