Norway’s safety watchdog is to launch an investigation into what it terms a "serious" incident in which a rig’s blowout preventer became blocked during drilling work for Neptune Energy at the Gjoa field.

The incident occurred on 20 September while the Odfjell Drilling-operated semi-submersible rig Deepsea Yantai was drilling production well 35/9-G-4H at the North Sea field.

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After the well entered the reservoir, the drill string from the rig became stuck in the formation as it was being pulled out and separated into two sections.

These parts of the drill string then blocked the BOP, resulting in the latter being unable to close to prevent possible leak from the wellstream, according to the Petroleum Safety Authority (PSA).

The agency has classified the mishap as “serious”, although it said no discharges resulted from the incident.

Well planning scrutiny

A cement plug has now been inserted against the reservoir to restore safety barriers, with work still under way to remove the two drill string sections from the BOP.

The PSA said its investigation team will get to work immediately to identify the causes of the incident and determine lessons that can be learned to share with the industry.

“It will concentrate on the planning of the well and implementation of the drilling operation up to the point when the incident occurred,” the agency stated.

The Deepsea Yantai has been lined up to drill a pair of exploration wells early next year in the vicinity of Neptune’s recent Dugong discovery, as well as for the second phase of development drilling at the Fenja field project in the Norwegian Sea, after Neptune extended its charter for the unit with rig owner CIMC Raffles last month.