Reduction of fluid density based on pressure points measured in the reservoir leading to kick

Course of events:

• Drilled 6x7" hole section, ran screens and set hanger.
• Displaced from 1.18 SG drilling fluids to 1.05 SG brine.
• Closed in based on 600 l influx (PP estimated to be 1.09 SG)
• Circulated out gas and displaced to 1.15 SG brine (using drillers method)

What Went Wrong?:

Factors which contributed to the incident:

• Brine weight reduction
• Pore pressure prognosis
• Lack of pressure point coverage of all sands during drilling

Corrective Actions and Recommendations:

• Several pressure points where taken in the reservoir and these were used to reduce to mud weight from 1,08 sg to 1,05 sg brine. This reduction turned out to result in too great a weight decrease, since there were two small sand zones exposed that where not picked up on the log. It is important not to place to great a reliance on pressure points taken during the section, since there can be small zones that have not been caught on the log that may have a different pressure.
• Instead of displacing the well to kill mud during the second circulation of the drillers method, the team decided to displace to a higher weight brine. This meant that they would continue operations faster, after the kill, than would have been the case if they displaced to drilling mud.

safety alert number: 269
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/

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