Offshore regulator, the Canada-Nova Scotia Offshore Petroleum Board (CNSOPB), has permitted Shell Canada to resume drilling with restrictions at its Cheshire L-97 exploration well offshore Nova Scotia.
Drilling was halted on March 5th after an operations incident on the Stena IceMAX drillship.
After securing the exploration well with two barriers and disconnecting to ride out heavy weather, the riser was accidentally dropped to the seafloor. No one was injured and no well fluids or synthetic oil-based drilling fluids were spilled to the environment.
The offshore regulator said that its review confirmed that the crew of the Stena IceMAX appropriately prepared for heavy weather in the days leading up to the incident on March 5th by suspending drilling, installing two barriers to secure the well (a downhole plug and the closing of the Blowout Preventer, BOP), and displacing drilling fluids in the riser to sea water.
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 so as to protect the integrity of the well, the tensioner system holding the riser was fully retracted.
The key factors in the cause of 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 (RARS) inactive.
For the past three months the CNSOPB said the agency has thoroughly reviewed the incident and investigation report. It engaged independent, outside, world-class expertise in deep-water drilling to provide additional oversight.
Aberdeen Drilling Management (ADM) worked with the CNSOPB in the review of the incident, the work procedures, the investigation report and an assurance plan that CNSOPB required from Shell Canada, to determine whether drilling can be safely resumed, and, if so, under what conditions.
“This has been a rigorous and exhaustive review of the incident,” says CNSOPB CEO Stuart Pinks. “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. As an additional safeguard, the CNSOPB has introduced a condition further tightening operating limits under which drilling may occur.”
Until such time as the CNSOPB completes further reviews, Shell Canada is required to lower its well disconnect criteria on the Stena IceMax based on vessel heave of five metres. The previous criteria was eight metres.
Before permitting a return to drilling the CNSOPB sought and received assurance on a number of matters arising from the review of the incident and the investigation report. These included:
Equipment – That all repaired and replacement equipment is certified, installed, commissioned, tested and compliant.
Procedures – That procedures and operational criteria are reviewed and amended, where applicable, with specific focus on updated disconnect procedures and the use of weather forecasting.
Training and competency – That people are trained and fully aware of changes to procedures, their roles and responsibilities, and are specifically aware of weather related disconnect criteria. In addition, disconnect drills and simulations are conducted to ensure that personnel in positions critical to the disconnect process are fully conversant with revised procedures.
Risk Management – That a review of the incident investigation findings and learnings related to equipment, work procedures, and personnel competency be conducted to ensure risks are ALARP (as low as reasonably practicable).
Pinks says the CNSOPB continues to review the incident, including the investigation report, to determine if future regulatory actions or changes are required. No decisions have yet been made with respect to the riser that remains on the seafloor.