Abstract
Offshore pressure boosting operations are conventionally performed with pumps and compressors situated on a large and expensive platform. In addition to increased weights and costs, large offshore platforms place unnecessary risk on personnel due to higher maintenance requirements, leading to increased offshore presence and helicopter operations.
This paper provides an overview of a hybrid topsides and subsea boosting facility that reduces risk, weight and cost.
To deliver a step change in safety and realise significant cost savings, Aker Solutions has leveraged subsea design thinking to develop a hybrid, lightweight, unmanned compression facility. We have used an approach where every system has been technically justified as essential to operation and adopted new design, operating, manning and maintenance philosophies. All equipment selected for this concept has project references and the facility could be executed today without the need for further technology development.
The resulting design is comprised of three components:
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Subsea module: Well fluids are separated subsea, with gas being sent to the topsides facility and the liquids being boosted to export pressure via a subsea pump.
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Unmanned platform: Wet-gas is compressed topsides using liquid tolerant hermetically sealed electric drive compressors, before being cooled and returned subsea to be mixed with the liquids.
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Power, communications and controls: Provided from a nearby host facility or from shore via umbilical.
The flexible and easily scalable topsides are simplified as only compression systems, operated and powered from a host facility, are on the platform. This reduces offshore maintenance and therefore allows unmanned offshore operations where maintenance personnel are only permitted on the platform following shutdown and depressurization.
Early modelling suggests that compared to a conventional compression platform, weight savings of more than 50% and an overall cost saving of up to 50% may be achieved.
As unmanned offshore compression is novel, this paper will provide insight into how such a facility could be engineered, as well as the safety and cost benefits that can be achieved through its implementation.
