This is a first for the offshore industry, Island claims, and could be a safer and cheaper alternative to traditional drilling using a rig.
MOU Island Constructor drilled the shallow pilot hole down to 360 m (1,181 ft) below mudline at the field location, north of Ekofisk in the southern Norwegian North Sea, to log for potential gas. If this was discovered the hole was to be cemented.
Pilot holes are drilled to investigate the presence of shallow gas in formations in advance of drilling of production wells. Hidden gas pockets encountered at a depth close to the surface or mudline can lead to blowout during the early stages of drilling.
Island’s project manager Anders Olsen said: “The risk involved with using a rig compared to a vessel is also considerable as it will need far more time to move away should a blowout occur.
“In addition the coil tube’s flexibility makes the vessel able to keep pumping mud down the well to stop a potential shallow gas blowout, while moving to a secure area.”
Instead of using a marine riser, the coil tube is kept in tension between the vessel and the subsea injector via a second injector installed on board.
The tube does not rotate, but pressurized fluid inside the coil activates a hydraulic motor which makes the bit rotate. The subsea injector pushes and pulls the coil tube in and out of the well.
“We have aimed for this since 2009. With coil tubing one can perform heavy maintenance to increase production and squeeze more oil and gas out of the wells,” said Island’s department manager top hole drilling Per Buset.
The operation at Butch was planned to last for seven days, but was completed in just over four without finding shallow gas.
Moving a rig and other equipment on the seabed due to shallow gas can incur costs of several hundred million kroner, Buset added. “By using our alternative method Centrica has, according to their calculations, saved roughly 30-50% compared to using a rig.”
Island is the developer and owner of the technology which is integrated with Baker Hughes’ topsides equipment. It aims to apply the same principle for light well intervention, plug and abandonment, and other types of well intervention.
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