Well Control Incident

• While drilling 8"1/2 hole section @ 5052m with 1.51 SG MW, observe well flowing during pipe connection. Shut well in w/ 76 bbls gain. Establish 550psi SIDPP and 970psi SICP.
• It took more than 7 minutes for the Driller to shut in after the well flowing situation was recognized (9 minutes 52 seconds total pumps off until well shut in) as follows: "The Mud Logger calls the dog house to inform the Driller that he has seen a gain in the trip tank; the Assistant Driller takes the call and communicates the information to the Driller. As the Driller is in the process of raising the blocks, he waits until the blocks are at 26m and calls the pit room to check that there is nothing that would affect the trip tank volume. He then waited for the return call which confirms nothing would affect the trip tank. The Driller switches over to the flow line as the trip tank is now nearly full and then lowers the TDS and screws back into the string at the rotary table. The string is then picked up and spaced out to close the annular mid joint; the Driller then unlocks the compensator. The annular is then closed by the Assistant Driller who is at the panel and the lower fail safes on the choke line are opened to monitor pressures."
• Well was controlled using Drillers Method to circulate/increase MW up to 1.63 SG & decrease gas levels prior to open the well.

What Went Wrong?:

• Kick zone actual PP exceeds predicted PP range by ~0.07 SG EMW.
• But actual PP < ECD (well not flowing while pumping).
• 76-bbl Kick Volume due to lengthy shut in Vs. ~30-bbl actual Kick Tolerance (KT) calculated from actual ~0.1 SG EMW Kick Intensity (design KT was 80 bbls calculated from maximum predicted PP). Note: There was gas in the influx, but no H₂S. According to kick pressure & volume analysis, it is possible that part of the kick was liquid (influx density calculation). Influx density helped evacuating the kick w/out exceeding MAASP & fraccing @ shoe on exceeded KT.

Corrective Actions and Recommendations:

1. Flow check each connection prior to starting the physical breaking of the tool joint (rather than flow check during connection).
2. Ensure effective monitoring of the Mud Logging fingerprint screen during pumps-off real-time (connection & mid-stand "long connection test”).
3. Correct shut-in procedure to be enforced & applied.
4. Perform unannounced simulated kicks (kick drills).
5. Whenever possible, implement a Well-Full-of-Gas capable casing design so that KT is not limited.

safety alert number: 257
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/

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