IOGP Well Control Incident Lesson Sharing
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Influx while drilling a reservoir section while using Managed Pressure Drilling


An influx was taken while drilling the reservoir section using Managed Pressure Drilling (MPD). While drilling the 6-3/4 section (directional - sliding phase) with MPD, there was an observed flow out increase. Attempted to circulate with MPD as per procedure, increasing back pressure but no success. The well was still flowing, and a high amount of gas was observed at the treatment unit. Drilling was stopped, annular preventer closed (observed surface back pressure drop and additional gain while doing so). Pump kill mud.

What Went Wrong?:

A very sudden gain of 60 bbls was detected while drilling through the reservoir section of the well. This amount of volume significantly affected the hydrostatic in the well. The MPD system in auto-mode (controlling a surface back pressure constant) was not able to keep a bottom hole pressure constant. With such a large gain, the well had to be shut-in conventionally. When they attempted to shut the well in on the annular preventer, they noticed a drop surface back pressure resulting in an additional gain. Both the BOP master/command system and the MPD auto choke were incorrectly rigged up on the same rig air supply. When the annular BOP was activated, the accumulator unit did start the pneumatic units to build back the control pressure, the rig air pressure dropped slightly which triggered an unexpected opening of the MPD auto-choke which led to the additional gain.

Corrective Actions and Recommendations:

While drilling through the pay zone they took an unexpected influx that resulted in the incident. Heightened awareness prior to drilling the pay zone may have helped to catch the influx sooner resulting in a more manageable kick volume. When the well was shut in with the annular preventer, the crew had to switch from MPD mode to manual mode. A better understanding of these procedures may have also helped reduce the amount of gain taken. When the annular closed, the rig air pressure dropped and caused the MPD choke to open due to being rigged up on the same supply line. Practicing well control drills switching from the MPD mode to manual mode, function testing, or simply double checking the way the system was installed may have uncovered the issue with the two systems being rigged up on the same line thus preventing the additional gain. The lessons learned concerning the incorrect rig up were shared, checked, and corrected for future MPD operations.


safety alert number: 307
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/

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