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Portable RLWI Deployment

Expanding vessel capacities with on-demand Riserless Light Well Intervention


Over the years, MDL has been approached by a number of global offshore contractors looking to expand their service offering into wider Life of Field operations, by enabling their vessel fleet to perform new operations - such as Riserless Light Well Intervention (RLWI). They had reached out to MDL because of our reputation for designing portable equipment which can convert bare-back vessels into lay and retrieval solutions - which work first time out the box. The aim of this approach towards RLWI is to upgrade their vessels' capabilities, rather than challenge those of a drilling rig.

MDL Approach

The philosophy behind MDL RLWI designs is based on the proven benefits of MDL’s Portable Vertical Lay System (PVLS) as a prime enabler. This approach, along with the addition of project-specific key ancillary items, adds value to the vessel - typically a monohull - without the need to undertake a dry dock, re‐fit or major vessel reconstruction. This is achieved by designing and manufacturing standard module-based components which can be handled at any dockside with access by road and a suitable assembly area. The costs can be reduced further by utilisation of the vessel's crane for mobilisation and demobilisation activities. This solution provides efficiencies for vessel ‘conversions’, which are measured in days and not weeks when comparing with integral towers typically used for RLWI operations. The conversion can be reversed and the system transferred to alternative vessels cost effectively should the need arise.

MDL Solution

MDL RLWI is a modular open-frame construction, supplied to the mobilisation port by road in components along with the standard grillage and other supporting assets. The units are integrated prior to the complete assembly being lifted on‐board, optimising the vessel time alongside. The Grillage Foundation supports the tower to distribute the loads into the deck structure, minimising any requirement to provide additional deck strengthening. The tower can be located over the side of the vessel, forward or aft of the moonpool. The tower configuration consists of two columns constructed by bolting modules together, which enable the height to be adjusted by the addition or removal of modules to accommodate the RLWI’s longest component. Cursor frame guides on the tower’s columns along with the cursor frame to stabilise the RLWI packages during deployment and recovery. An X‐Y skidding package is located on the vessel deck, configured in a manner that provides the delivery and parking of equipment and services required by the RLWI operations. The hydraulically-actuated work platform offers a safe and convenient working environment for personnel, and can open to full width of the RLWI component to facilitate efficient subsea deployment. Another feature are the stabiliser arms used to extend the operational weather window. These attach and disconnect from the RLWI package using a dedicated device (ask us about the Halo if you want to know more).

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