Shell Canada Ltd. may have abandoned the first of its deepwater wells off Nova Scotia, but questions remain on what to do about an undersea coil of steel pipes – each weighing at least 20 tonnes – left on the seabed of the Scotian shelf.
The pipe and the drilling equipment plunged to the ocean bottom on March 5 when the contracted Stena IceMax drilling ship unlatched from the well in heaving seas and lost control of the two kilometres of steel gear.
Since then, both Shell and the Canada-Nova Scotia Offshore Petroleum Board have said options are being examined for the roughly 800 huge pipes that lie around the abandoned wellhead over an area about the length and width of three football fields.
There is also a 114-metric-tonne drilling apparatus known as the "lower marine riser package" that is embedded in the seafloor near the well, which Shell has said is now plugged due to a lack of oil.
Shell spokesman Cameron Yost and a spokeswoman for the regulator confirmed on Wednesday that options are still being considered.
However, an environmental study prepared for Shell Canada and obtained by The Canadian Press describes some environmental consequences of two choices: leaving the pipes in place or sending down submersibles to cut up the sections and bring them to the surface.
In its review of the first option (leaving the pipes in place), the report by Stantec Consulting says the area isn't known to contain "high-value or vulnerable" fish habitats or coral, and the presence of the pipes on the bottom "could possibly improve habitat quality ... by creating an artificial reef effect."
It also says the water is so deep it's unlikely fishermen would hit the pipes with their gear and the location could be documented in a notice to seafarers.
Still, it also says over long periods of time "buoyancy modules" attached to the pipes – each large and heavy sections on their own –could "become loose and detach, rise to the surface and become floating debris that could drift away from the offshore wellsite location.
Six of the eight dislodged modules have already been removed, says the report.
The report says the second option of cutting the pipes would stir up the seabed, disturb habitat and create underwater noise for six months or more.
"It is possible that despite best management practices, substantial amounts of debris could rise to the surface during cutting and recovery," said the report.
"This debris may interact with fishing gear and persist in the marine environment for an indeterminate amount of time."
The debris could pose harm to fish, marine mammals and turtles if ingested, it adds.
The report doesn't recommend one option or the other, saying each is feasible provided recommended mitigation measures are taken.
In the case of leaving the gear on the bottom, the report says a notice to mariners should be published, while in the case of cutting up the pipes, the company would have to follow regulatory requirements and environmental rules.
The company said in an e-mail that the buoyancy modules are attached to the pipes with three-quarter inch stainless steel studs.
"In the unlikely event that over time any of the deep-rated buoyancy modules degrade and float to the surface, the probability of the debris encountering marine traffic as it ascended would be very low due to the short period a vessel would be transiting through the area where the riser is located."