Seabed electric oil/gas processing system near completion

Water separation cuts production costs

Jul 1st, 1999
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Production of the first ÆSOP (all electric seabed oil/gas processing) module is nearing completion at the Kockums Engineering yard in Malmo and continues on schedule for demonstration to the offshore industry in September. Kockums managing director Sven-Ake Nilsson is confident that the new unit will be welcomed by the industry as its subsea production capability will bring significant cost benefits.

Estimates suggest that it could boost well production by up to 75% and development of the system is being supported by a consortium that includes Conoco (UK), British Borneo Oil and Gas, Shell UK Exploration and Production, and Statoil (Norway). The European Union is also providing funding for the demonstration project.

ÆSOP is utilized autonomous module for use in an AlphaPRIME system and incorporates electrically powered flow control and processing units. It was engineered by Kockums' UK subsidiary Alpha Thames in response to the trend towards seabed systems being completely electrically powered and controlled.

A preliminary study confirmed that an electrically powered and controlled seabed oil separation and boosting system is feasible especially if it is part of an AlphaPRIME modular seabed processing system. "We realized that subsea processing will be big in the future and we acquired Alpha Thames who had the idea to package machinery on the seabed," said Nilsson.

AlphaPRIME is a diverless modular system that is completely retrievable for re-use and allows for the packaging of modules such as ÆSOP in a variety of configurations to suit specific field requirements. An AlphaPRIME system can be tied back long distances to a floating, fixed, or shore-based production facility, even beyond 50 km distance. The system can be optimized to maximize field output, through manifolding, pumping or seabed separation. The modules provide a means of readily installing and retrieving seabed equipment without the need to shut-in any of the wells.


AlphaPRIME system offers versatility for seabed installations.
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High power

The system can be installed in water of any depth and begins with the positioning of the main seabed structure and the connection of the power supply. The use of high voltages underwater has been made possible by a technical breakthrough by Alpha Thames that eliminates the problem known as "water treeing." With power available the installation of the docking manifold follows.

This includes a multiple pipework connector known as MATE that allows the simultaneous connection or disconnection of various combinations of pipework sizes to suit the process requirements. Both halves of the connector are internally valved to contain process fluids when separated. MATE can be used to isolate subsea production systems and allow process equipment to be retrieved for surface maintenance without the need for a field shutdown.

Flow line tie-in is achieved with a connection system known as CUSP that enables connections of rigid or flexible pipelines, electro-hydraulic umbilicals, the remote retrieval of valves and pipeline repairs. The system has been designed to dramatically reduce the complexity of these subsea operations by accurately aligning the pipeline ends, which it then clamps, locks and seals in a single operation. The connection system comprises a compact lightweight installation tool containing the connector that can be flown with a standard work class ROV and readily deployed from the smallest support vessels.

A minimum of two production modules would normally be installed, each weighing 25-80 tons, depending on field characteristics, and lowered from surface ships onto the docking manifold. The modules are self-aligned and cushioned against impact by the MATE connector as it is docked. Once installation of the module to the docking manifold is completed, start-up begins. Installation and operation is not, however, the end of the story as the modules can be retrieved later with equal ease for maintenance or for the installation of additional production capabilities such as gas and/or water separation as the characteristics of the field change during its life cycle. This is all achieved without the need to shut-in production.

When the AlphaPRIME system enters service, it has been calculated that it will reduce combined CAPEX and OPEX production costs by £2-3/bbl, a figure that includes investment and maintenance. By separating water on the seabed, where it can be re-injected, the operator is not paying to pump it to the surface and could ultimately eliminate the need for FPSOs. Because AlphaPRIME can be situated a considerable distance from surface facilities the system will re-write the economic rules for satellite fields. The problems associated with hydrates and multiphase flow will also be eliminated and the system will justify the reactivation of abandoned fields.

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