Unexpected geology and compromised volumes tracking result in a kick
IOGP’s Well Expert Committee receives notifications when a member company has experienced a well control incident that could provide learnings to IOGP members and the industry.
In a recently reported event, an Operator was drilling a 12-1/4” hole in the reservoir section of an exploration well. A 15 barrel kick was taken and the well was killed. During riser circulation following the well kill, the diverter had to be closed due to expanding gas in the riser.
The event described above presents a good reminder of the importance of the early kick identification and the value of frequent flow checks. A few questions to consider:
- How does your company handle additions, dilution, or treatment of the drilling fluid in the active pit system while drilling in or near the reservoir section in exploration wells? Is it different for development wells in a known area?
- How long should rig crews wait to perform a flow check once indications of flow are observed? How does the size and rate of gain influence the decision to perform a flow check? Have you discussed and set limits/parameters for flow checks?
- In your operations, as confidence in the expected geologic prognosis increases, is willingness to heed well control warning signs diminished? Was complacency an issue in the event described above?
- What could have been done to avoid the riser unloading event?
Note: Original alert wording from IOGP Member Company.
Incident description
12 1/4 Drilling on an exploration well in the reservoir - getting close to well TD. Pore pressure and reservoir depths have closely followed the geological prognosis so far.
While drilling perform active pit density increase in order to provide a tripping safety margin. Observed slight increase in the active but consider it caused by the mud treatment - continue drilling still monitoring that slow gain. After a while stop drilling/treatment/crane movement and perform a flowcheck - well flowing. Shut the well in. Observe riser stable, perform well control circulations to kill the well. During the circulation of the riser, experienced gas expansion and had to divert riser content overboard.
What Went Wrong?:
- Overconfidence in the prognosis, entered unexpected layer with a significant kick intensity (+0.20 SG / +2 ppg).
- Pit discipline, performed treatment in active pit while drilling - delaying the diagnosis of the initial gain and the required shut in action.
- Same cause has allowed some gas to be circulated above the BOP generating a situation of gas in riser.
Corrective Actions and Recommendations:
- Active pit monitoring discipline - no treatment allowed during drilling a reservoir section.
- Review and consolidate gas in riser procedure - train the crews.
safety alert number: 306
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/
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