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Image courtesy of Shell/Flickr.

Shell Canada said Thursday that it has been cleared to resume drilling in Nova Scotia following an accident review.

The Canada-Nova Scotia Offshore Petroleum Board (CNSOPB) has permitted Shell Canada to resume drilling with restrictions at its Cheshire L-97 exploration well.

Drilling was halted on March 5 after an operations incident on the Stena IceMAX drillship.

Shell said that the incident occurred when a riser was accidentally dropped to the seafloor after the exploration well was secured with two barriers and successfully disconnected to ride out heavy weather.

No one was injured and no well fluids or synthetic oil-based drilling fluids were spilled.

Shell said the CNSOPB review confirmed that the Stena IceMAX crew of “appropriately prepared for heavy weather in the days leading up to the incident”  by suspending drilling, installing two barriers to secure the well, including a downhole plug and the closing of the blowout preventer, and displacing drilling fluids in the riser to sea water.

The review found that when vessel motion exceeded the operational limits, “the decision was made to disconnect and ride out the weather with the riser attached to the vessel through the tensioner riser system, a standard procedure.”

To maximize the distance between the bottom of the riser and the BOP to protect the integrity of the well the tensioner system holding the riser was fully retracted, the review found.

The review found that the key factors that caused the incident were “the heave of the vessel and the inability of the riser tensioner system to compensate for the difference in the movement between the riser and the vessel with the tensioner system in a fully retracted position and with the Riser Anti-Recoil System inactive.”

Shell Canada is required to lower its well disconnect criteria on the Stena IceMax based on vessel heave of about 16 feet until the CNSOPB completes further reviews.

The previous criteria was about 26 feet, or eight meters.

Before drilling was allowed to resume, the CNSOPB received assurances that all repaired and replacement equipment is certified, installed, commissioned, tested and compliant.

Shell Canada assured that procedures and operational criteria were reviewed and amended, where applicable, with specific focus on updated disconnect procedures and the use of weather forecasting.

The company also assured the agency that workers are trained and fully aware of procedure changes and that disconnect drills and simulations have been conducted.

Shell Canada also told the CNSOPB that a “review of the incident investigation findings and learnings related to equipment, work procedures, and personnel competency” will be conducted to ensure risks are as low as reasonably practicable.

“We are satisfied that the cause of the incident has been properly determined and that appropriate corrective actions have been taken so that drilling may resume safely,” CNSOPB CEO Stuart Pinks said.

Pinks said the CNSOPB continues to review the incident, including the investigation report, to determine if future regulatory actions or changes are required.

The agency has not made any decisions with respect to the riser that remains on the seafloor.