Island Offshore Aims for Riserless Heavy Well Intervention

Following a successful deployment of its riserless coil tubing (CT) technology in the offshore petroleum industry, Island Offshore is said to be taking it to the next level by performing heavy well intervention with coil tubing in producing subsea wells.

In 2015 Island Offshore made history when drilling a pilot hole for Centrica by means of riserless coil tubing, in order to check for shallow gas at the location.

“The system comprised of a relatively standard coil tubing spread from Baker Hughes, rigged up on the LWI vessel Island Constructor in combination with a custom made subsea coil tubing injector and a subsea guidebase solution from Island Offshore. Specialized drilling procedures allowed unconsolidated sand and shale formations to be drilled safely without any major issues,” says manager for Top Hole Drilling and P&A Activities in Island Offshore, Per Buset.

Instead of using a rigid work-over riser, the coil tubing is kept in tension between the vessel and the subsea injector by means of a second injector installed on board the vessel. Pressurized drilling fluid pumped into the coil tubing drives the mud-motor which makes the bit rotate. The subsea injector pushes the coil tubing into the well creating weight on bit, and pulls the coil tubing out of the well when drilling is completed.

“The next step will be to adopt the system to perform heavy intervention with coil tubing in subsea wells. Intervention in subsea wells today are performed from Light Well Intervention (LWI) vessels, with wireline through a subsea lubricator. Obviously, wireline has its limitations compared to coil tubing,” says Buset.

Heavy intervention with coil tubing are rarely done, due to the high cost and challenges with meeting good HSE-standards. Using coil tubing for heavy intervention today requires use of a drilling rig and a complex work-over riser-system.

Island Offshore believes that a more reliable and less costly way to do heavy intervention in the future will be to run the coil tubing in open water without a workover riser system; same methodology as for LWI with wireline through a subsea lubricator.

For the coil tubing application, a subsea injector (controlled and powered by a ROV), will be installed on top of the subsea lubricator. Island Offshore have built the innovative injector and is now awaiting the delivery of a stripper element between the subsea-injector and the subsea lubricator in order to hold back pressure from the well. As soon as the stripper is qualified for offshore use, Island Offshore said it could offer heavy well intervention in producing subsea wells with coil tubing, perhaps as early as second/third quarter 2017.