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Kick taken while drilling 8 1/2” reservoir section in deepwater exploration well

• The event took place on a Drillship while drilling the 8-1/2” section of an exploration well.
• Well architecture consists of 36” CP at 939 m, 20” casing at 1274 m, 14” casing at 1666 m and 9-5/8” casing at 2702m.
• Drill 8-1/2” section at 2860mMD/RT.
• Made connection, resumed drilling.
• Observed 4.5% connection gas.
• Observed gas increase to 27%.
• Picked up string off bottom & circulated out gas (reciprocating string).
• Observed 0.9m³ gain in active pit while circulating gas out of hole.
• Shut in well & monitored for pressure evolution.
• Observed increase in SIDPP, SICP & WHP.
• Continued to monitor pressure evolution.
• Pressure stabilized at: SIDPP 480 psi & SICP 320 psi.
• Spaced out and hung off string on Middle Pipe Rams.

Observation:

• ECD increase. SPP increase. Possible change in formation.
• Sign of under-compaction on the resistivity log. Well Control: (Driller's Method).
• Flush each of Lower, Middle and Upper Choke fail safes. 131 psi (9 bar) back pressure on Choke.
• Circulate down string and flush KL. 203 psi (14 bar) back pressure on well.
• Open MPR and reduce UAP pressure. Close CMC.
• Attempt to strip up and down, negative - string differentially stuck. 40 MT over pull and 36 MT set down weight.
• Displace riser through boost line to 1.42sg kill mud. 17.7% max. gas observed.
• Displace choke line volume to 1.42sg kill mud
• Close MPR, displace KL with 4.5m3 base oil.
• Open UAP allowing 1.42sg kill mud in riser to u-tube up KL to sweep BOP stack.
• Observe 2.5m³ drop in trip tank volume. Close UAP and open MPR.
• Displace kill line volume to 1.42sg kill mud through gas relief line.
• Perform flow check: well static.
• Work drill string free with different parameters.
• Circulate down string: FR 380 - 1000 lpm, 624 - 1305 psi (43 - 90 bar). Apply 14KN.m, 36 MT below SOW and 45 MT overpull.
• Increase torque to max of 22.5KN.m. Observe drill string free.
• Displace Choke, Kill & Boost lines to 1.47sg NABM.
• Displace well to 1.47sg NABM.

What Went Wrong?:

• Failure to recognize the potential/risk: Despite warning signs and pre-job meetings alerting on the nature of the activity, crew was not vigilant and sensitive to the nature of the activity (exploration drilling).
• Underbalanced Well Warning signs missed: Mud loggers and Geologist not following properly the gas and resistivity trends and not communicating adequately on gas and under-compaction trends seen.
• Procedure not followed: Established procedure called for reducing BGG to <1% at all times before drilling resumes. Drilling resumed with high BGG.
• Poor supervision : With warning signs of kick, team failed to recognize the appropriate action to take. And signs of entering high pressure zone unrecognized.

Corrective Actions and Recommendations:

• No mud transfer should be done when drilling an exploration well without proper and laid out procedure. Follow mud transfer protocol.
• After each connection and flow check, the corresponding bottoms-up circulation must be monitored.
• Drilling of exploration wells should not have continued with 10% background gas.
• Fingerprint of flow back in active system during pumps shut off should be monitored and analyzed.
• The well site geologist should do more to alert the company man of such observations as decrease of resistivity log.
• As a follow up, drillers should charge the mud loggers to employ more monitoring tools like ROP break, d-exponent….etc, that give direct indication of a kick.
• Consideration should be given to having a manual joystick on the cyberchair for choke control. The buttons on the digital display is too small to operate.
• There was no kill sheet available by the time the kick was taken; not with the drilling contractor or company representatives. Going forward, a kick sheet should be prepared for every phase where a reservoir is to be encountered, compulsory for exploration wells. Kick sheet must be reviewed as operation progresses.
• Communication with base is mandatory in this type of event.

safety alert number: 263
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/

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