Aberdeen: DNV has taken Expro’s new AX-S deepwater subsea well intervention system through a feasibility assessment designed to demonstrate the viability of the innovation to stakeholders and investors. AX-S will make well intervention possible without the need for drilling rig or riser system in waters up to 3,000m deep.

AX-S will be suitable for well intervention operations from a dedicated monohull vessel. The intervention is performed on the seabed and is fully enclosed with automated tool change-out. The system follows a dual-barrier philosophy and does not require making or breaking pressured connections.

There is no need for stuffing box or grease injection, eliminating fluids from the well or controlling seawater ingress to the well and no hydrocarbons need to be brought to the surface. The system is suitable for operation with standard remotely operated vehicles (ROVs) and has real time data-to-surface communication capabilities.

DNV sponsor Robbie Williamson says the project created some challenges for DNV. “Most of the components of the AX-S system are new technologies with limited experience available from other applications”. “There were over 150 components that needed DNV’s assessment of their design and mechanical functionality.”

DNV’s Recommended Practice (DNV-RP-A203) provides a recognised technology qualification process that considers each part of a new technology individually and as a system and qualifies it to the applicable industry standards. Failure modes are examined and a cost/benefit analysis is undertaken on the risk reduction measures that are identified.

“Some of the key challenges the AX-S system faces are the pressures and temperatures that will be experienced at depth. This is particularly the case for the rotational sensors of the winch package, for which no off-the-shelf options were available,” said Matthew Svensen, DNV senior engineer.

In a paper prepared for Offshore Europe 2011 and co-authored by Robbie Williamson of DNV and Matthew Law of Expro AX-S Technology, Mr Svensen describes the processes and workshops that were undertaken to address more than 225 potential failure modes to give stakeholders and investors confidence in the new technology.

No show stoppers were identified and AX-S is expected to reach full commercialisation in the second half of 2011.