Introduction

As part of the 1989 work program, Esso Australia Ltd., operating on behalf of the Joint Venture between BHP Petroleum and Esso Exploration and Production, Australia, was to lay some 180 kilometers of pipelines and umbilicals to service new developments.

WHITING PROJECT

Whiting is the first unmanned platform to enter service in Bass Strait. The jacket and deck were installed by McDermott's construction barge, DB101 in March of this year. The 1,300 tonne jacket was also the first to be lifted directly from a cargo barge and upended on its location. The production facilities on Whiting required a 250mM oil line and a 200mM gas line to be laid across the 14.6 kilometres from Whiting to Snapper host platform. Risers were also to be set on Snapper.

SUBSEA COMPLETIONS

Two Subsea completions are part of this years work program. They are Seahorse, which is located 11.3 kilometres from the Barracouta host platform, and Tarwhine, which is 17.5 kilometres from Barracouta. Each of these projects required insulated flow lines, which projects required insulated flow lines, which consisted of 150mm production pipe encased in a 250mm carrier pipe for Seahorse and 200mm production pipe encased in 300mm carrier for production pipe encased in 300mm carrier for Tarwhine. The annulus was insulated with Polyurethane foam. To support production from Polyurethane foam. To support production from these wells, each required 70mm gas lift lines plus electro-hydraulic umbilicals to service plus electro-hydraulic umbilicals to service the control systems. For stability, the gas lift lines and umbilicals were trenched.

As part of this installation, new risers and 'J' tubes were installed on the Barracouta Platform. Platform.

SMALL FIELD DEVELOPMENTS

Gravity based monotowers were programed for the Perch and Dolphin fields. These structures, another first to Bass Strait, were installed on the Perch and Dolphin fields. They are isolated from other Bass Strait developments and as a consequence it was decided that the pipeline route would not tie into existing offshore facilities, thus necessitating a new Beach Crossing North of the township of Seaspray and a new landline would tie production directly to our Longford processing facility. The distance from the processing facility. The distance from the shore approach to Dolphin is 19.1 kilometres and from Dolphin to Perch is 11.9 kilometres. A common system consisting of a 300mm production line and 100mm gas lift line was production line and 100mm gas lift line was selected. These lines include a Tee piece to tie in at Dolphin and both systems tie into preinstalled risers on the monotowers. Both of preinstalled risers on the monotowers. Both of these lines were trenched for stability.

COST CONSIDERATIONS

In the budgets for these projects, considerable cost reduction had been attained for the installation of the jacket and production facilities with the result that the cost of fabricating and installing pipelines was an increasing portion of the project budget. It was therefore necessary to adopt techniques, which would reduce expenditures associated with the installation of pipelines. Bottom tow, which had been utilised successfully in previous projects, was considered to be a high previous projects, was considered to be a high risk method here because of the length of the lines would have required numerous field joints.

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