Control system to simplify, cut costs of subsea landing string deployments

Offshore staff

INVERURIE, UK – Interventek Subsea Engineering has secured funding from the Oil and Gas Technology Centre in Aberdeen for development of a control system for a new subsea in-riser landing string.

An unnamed international oil company has also agreed to provide end-user expertise and design criteria feedback for the project. Interventek aims to deliver a function-tested prototype by the end of this year.

Landing strings are in-riser safety systems that interface with the subsea wellhead on the seafloor, allowing completion or well intervention activities to be performed safely from floating vessels.

They contain a subsea test tree within a BOP - the test tree includes large-bore hydraulically controlled valves to provide well control and cutting and sealing in order to rapidly shut-in the well and disconnect the vessel should an emergency arise, typically in bad weather or a drive off scenario.

The control system operates the valves within the test tree and tubing hanger running tool (THRT) and is said to provide all functions required in the landing string for running completions or performing interventions.

Current control systems are very large, weighing up to 50 metric tons (55 tons), and can be difficult to transport to and around a rig.

Typically, these comprise an umbilical, up to 3,000 m (9,842 ft) long and up to 100 mm in diameter, an umbilical reel, a surface control unit to deliver the hydraulic power and control the valves, and a riser control module to provide local accumulation and direct the hydraulic power to the valves and THRT.

All take time to rig up, can be at risk of damage, and are costly to service and maintain.

Interventek’s stated goals are to provide cost savings of around 70% and to reduce the cost of ownership by more than 50%. The weight of the new control system should be close to 10 metric tons (11 tons), with a smaller footprint.

This should lead to a 15-20% reduction in operational costs, the company claims, through reduced rig-up times, deck space, logistics, ancillary support equipment and personnel on board requirements.

In addition, the control system will make use of the company’sRevolution valve technology to reduce the number of hydraulic lines typically required, replacing these with electrical functions.

Interventek will be exhibiting at OTC next week on stand 1161-6, in the UK/Scottish Pavilion run by EIC/SDI, located in the NRG Center.

04/30/2019