This paper describes a conceptual design of a subsea well intervention unit. The Intervention Service Unit (ISU) is a fit for purpose monohull vessel.

Focus on operational efficiencies and cost reduction has been important in the design phase, while prioritizing solutions, which minimize health, safety and environmental (HSE) exposure.

Scope of work for the ISU is wireline operations, coiled tubing and pumping services, subsea equipment installation and maintenance, well clean-up, testing and coiled tubing drilling.

High operability in harsh environment, such as the northern North Sea, is a major design parameter.

The general section of the paper explains the basic engineering execution and the overall specification structure of the concept, from the generic Functional Specification through the more detailed Building Specification.

Some of the challenges which were identified and the unique solutions developed, are described. This includes work over open water and at elevated levels, splash zone issues, handling of heavy loads on a moving structure, amongst others.

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