The changing economics of oil and gas transportation mandate continued downward pressure on costs, and an increased reliance on shared or third-party provision of pipeline and processing plant capacity. Clearly, the ownership of commingled gas and produced liquids is a matter for negotiated contract agreements, which are routinely applied based on the volumes and compositions of delivered products. However, the management of gas flow to maximise deliveries and profits, and minimise contract violations, requires predictive simulation combining sophisticated pipeline and plant modelling. The Scottish Area Gas Evacuation (SAGE) system, operated by Mobil North Sea Limited, comprises the St Fergus gas processing plant and associated pipeline connections to the Beryl, Scott and Brae fields. Under the agreements entered into by the SAGE owners, the system must be controlled to ensure that sales gas delivered from the plant is the sum of specific, nominated amounts for each of the three fields. Additional agreements govern the distribution of the accompanying Natural Gas Liquids (NGLs) to the NGL processors, The first part of this paper discusses the implementation and architecture of the SAGE Allocation Management (SAM) system, designed to provide In-The-Day predictions of the results of the fiscal allocations, developed by the SAGE owners, to be performed at the end of each twenty-four hour period. These calculations are based on real-time data acquired from the pipeline and the plant, and rely on accurate predictions of the movement of composition fronts throughout the pipeline system. The paper emphasises the application of the system, demonstrating the range of functionality offered, and the flexibility and power of its true client-server foundations. The design ethos for the SAM system is appropriate functionality and ease of use; with this in mind the remainder of this paper is devoted to reviewing the use and expansion of the system over the past year and focuses on the benefits to the users.

1. Scottish Area Gas Evacuation (SAGE) System

The SAGE system currently transports and processes gas from the Beryl, Brae and Scott fields in the UK sector of the North Sea. The system is capable of transporting and processing up to 1150 mmscf (32.58 mcm) of gas per day. A thirty inch pipeline links the Beryl platforms 185 miles Northeast of Peterhead to a gas processing terminal at St. Fergus, five miles north of Peterhead on the Aberdeenshire coast. Spur lines link the Brae and Scott fields to the main pipeline which is maintained at pressures in excess of 1740 psig (120 barg) to ensure single phase operation. The SAGE Terminal processes feed gas, producing natural gas for export to the British Gas Terminal at St. Fergus, and Natural Gas Liquids (NGL's) for export to the Shell Terminal at St. Fergus and to the Forties System. The SAGE system is jointly owned by the Beryl Group and the Brae Group.

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