A/S Norske Shell needed to carry out tubing hanger crown plug (THCP) removal from a riserless light
well intervention (RLWI) vessel in the Norwegian sector of the North Sea. There were concerns that the
conventional application of mechanical jarring with slickline tools could not be used due to the combination
of deep water and high sea currents in the specific field. A safer, more controlled and assured method was
needed to withstand this extreme environment and provide the certainty of task success.
Theoretical studies and practical testing were conducted at the supplier's test site to verify the impact sea
current had on cables and toolstring assemblies. Different scenarios were analysed and the most effective
and lowest cost solution was determined. An electric line deployed and powered electrohydraulic stroker
device was selected, which did not require any cable actuation to generate the pull forces required to unseat
the crown plug.
Toolstring space-out was critical to ensure the stroker anchor was above and clear of the well control
package (WCP) and positioned to prevent any inadvertent damage to the lubricator. In addition, a release
tool and a shearable stem provided back-up safety capability for well control. A modification to an existing
stroker was designed and a prototype built and tested at the onshore facility.
The final stroker toolstring design was tested out successfully on a more benign shallow subsea well,
where the highly accurate force and movement control of the stroker, coupled with real-time surface readout,
enabled a safe and secure crown plug pulling and installation operation. The targeted operation in a deepwater,
high-sea current environment was then carried out successfully, applying many lessons learned and
process improvements from the trial well.
In conclusion, the use of electrohydraulic stroker technology was proved to be a viable alternative for
crown plug retrieval and setting operations, whilst bringing heightened visibility and control to such an