INTRODUCTION

The Occidental Consortium's newly developed "Scapa" field has now come on-stream as planned, some 14 months after Department of Energy approval The Scapa development consists of a major subsea facility connected to the Claymore platform, 3 miles* away by two pipeline bundles and associated control umbilicals (see Fig 1) The new topside facilities are connected in turn to the pipelines by a large bundle riser, carrying the produced oil and lift gas, with a facility for a utility if required The field is estimated to have recoverable reserves of 40 million barrels of oil with a gravity of 32 5 ° API to be extracted from a Lower Cretaceous reservoir

The Scapa development had a considerable engineering content The main production riser and template each required a large proportion of this engineering for the installation design It was a requirement that all of the subsea work should be completed with one season. To accommodate this the contracts were broken down into elements

  • template - fabricate and install,

  • bundle - fabricate and install

  • (Fig 1 is available in full paper)

  • riser-fabricate

  • riser-install

These packages therefore gave the flexibility to maximize the offshore work programme involving vessel availability and installation capacity This chapter gives a short overview of Scapa's facilities and installation difficulties, together with a fuller description of the riser and template

It should be noted with interest that the total weight of Scapa additions to the jacket is approximately 800 tomes, or 2 3% of Claymore's jacket and topside weight The structure's capability of accepting the extra load required verification

FACILITIES
Pipelines and umbilicals

The template is connected to the Claymore platform by an extensive pipeline system, consisting of two 28 m * multi-line composite bundles, an 8 in water injection line and a 3 in bulk chemical treatment line, as shown in Fig 1

Each pipeline bundle is approximately 2 8 miles long and contains a 10 in. production line, a 6 in test/service line and three 3 in gas lift lines. The bundles are connected to the template manifold and the platform production riser by flexible spools.

The two pipelines, which are the longest of their type to be towed to date, were installed using the mid-depth tow method. Using the natural buoyancy of the pipeline to raise the line off the sea bed and chains to control this flotation, the lines were towed using two tugs These tugs kept a set tension on the line during tow and the level of tow was varied depending upon the weather conditions. The towlines were attached to the bundles by specially designed tow heads These tow heads also served to splay the integral lines for accommodating the flange tie-in points. To confirm manual calculations, tests were carried out on a scale model of the tow head to determine.

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