This paper describes the design of a multiple pig launcher for installation on the MACHAR subsea production manifold, located 150 miles east of Aberdeen, in 300 feet water depth. The manifold forms an integral part of BP's Eastern Trough Area Project (ETAF') and is linked to the Central Processing Facility (CPF) platform by a 22 mile long subsea multi-phase pipeline. The length of this pipeline and the resulting temperature drop from the 120°C well temperature means that wax deposition is a potential problem. To maintain optimum efficiency frequent pigging operations will be required to remove the wax deposits. The ability to maintain this efficiency over the life of the field is fundamental to the economic viability of the whole field. This requirement has led to the development of an innovative design solution for the subsea pig launcher to enable single line subsea pigging operations to be carried out as an integral part of the pipeline maintenance programme. The design is based on optimising CAF'EWOPEX costs, utilising conventional surface vesselsfor deployment and the provision of a reliable, fail safe, ROV operated pig launch mechanism. Although pig launchers have previously been deployed for subsea use, the specific requirement for continuous operation as part of the pipeline maintenance programme will possibly be the first application of this type of equipment in the World.

The most significant aspect of this development is the provision of a reliable, cost effective, long term pigging facility for subsea operations based on simple operation and minimum intervention times.

Introduction : Background

Consent to start the 1.6 billion GBP development of the Eastern Trough Area Project was granted in December 1995. It involves the development of seven distinct fields each of which would have been marginal, stand alone, developments but have been combined into an integrated project by alliance partnerships. Fundamental to the Success of the project is the application of alliance working Concepts embracing the principles of the industry's CRINE (Cost Reduction initiative for the New Era) initiative. BP, with a 58% interest in the development, will operate the ETAP facilities on behalf of the partners : BP, Shell, Esso, Agip. Murphy, TOTAL and Mitsubishi Oil.

The fields involved in the development are Marnock. Mungo, Monan and Machar, Heron, Egret and Skua along with two future fields, Mirren and Scoter will be operated by BP. They have combined estimated reserves of some 400 million barrels of oil, 35 million barrels of natural gas liquids and 1.1 trillion cubic feet of sales gas.

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