Island Offshore’s award-winning riserless technology is making the jump from light interventions to heavier operations. Tim Skelton reports on the company’s plans for 2017
Having successfully proved its riserless coil tubing technology on several test wells, Norwegian marine engineering specialist Island Offshore believes it is ready to extend the process, enabling it to perform heavy subsea intervention tasks at producing wells. Instead of using a rigid marine riser attached to a fixed platform, Island Offshore’s design uses coiled tubing linking an open-water vessel to a subsea injector, with the waterproofed tube kept in tension by a second on-board injector. This provides flexibility and allows drilling to take place in remote locations where little or no infrastructure exists. Pressurised fluid inside the coil tube drives a hydraulic mud motor that rotates the drill bit, while the subsea injector places weight on the bit to move it into the well. Riserless drilling offers several key advantages. From a safety perspective, if a blowout or another well-control operation occurs the surface vessel can move away from the drilling site at short notice, while at the same time keeping the tubing in contact with the well, allowing mud to be pumped in to hold back a blowout. The risk of injury to personnel is also reduced. Riserless operations also result in reduced impact on the surrounding environment, as less equipment is required and less time is spent at the well site compared to a full drilling rig. Moreover, savings on manpower and lower capital expenditure make operations far cheaper.
Heavy going The technology was first tested in 2014 before making the jump to the oil and gas sector in 2015. Working with Centrica, Island used coiled tubing drilling linked to its Island Constructor mobile well-intervention vessel to drill a pilot hole to check for shallow gas at the former’s Butch field in the Norwegian North Sea. Centrica said the operation had saved it “about 30 to 50%” in costs. In August this year the success of the test led to the two companies jointly receiving the Innovation Award at the Offshore Northern Seas (ONS) conference in Stavanger. According to Island, all the advantages demonstrated in the test will apply equally when the riserless coiled tubing technology is adapted for heavy subsea interventions. The company says it will allow operators to perform heavy maintenance to increase production and reservoir recovery rates using less equipment and fewer personnel. Such maintenance could involve, among other things, the removal of sand, scale and other blockages to restore the original inner dimensions of production tubing, and general plug and abandonment (P&A) operations. Using coiled tubing for such work today requires a fixed drilling rig and a complex workover riser system, and this is rarely done owing to the high costs and safety challenges involved. Island says it can make these operations cheaper and more reliable by running the tubing through open water without a riser, and using similar methodology as the currently most popular method for interventions: Light Well Intervention vessels running a wireline through a subsea lubricator. To make this suitable for coiled tubing, a subsea injector controlled and powered by a remotely operated vehicle (ROV) will be installed on top of the subsea lubricator. Island has already built the innovative injector and is now adding a stripper element between this and the subsea lubricator in order to hold back pressure from the well. Once this is qualified for offshore use, it says it will be ready to offer the technology to the market for heavy interventions in subsea wells. This is expected to happen by the second half of 2017. In a recent company press release, Island Offshore manager for top-hole drilling and P&A activities Per Buset sounded upbeat about the technology’s prospects. “Oil companies rarely do heavy well intervention because of the high costs, but they have [often said] that if the cost is low enough they will do it. This will be a game-changer for intervention work in subsea producing wells, including the plug and abandonment market,” he said. “The potential for both oil companies and service providers is huge.”