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Shallow Gas leads to well control incident

• The well is located in a well-known, shallow gas prone area.
• Deep gas wells with high pressurized layers.
• Crowded platforms with wells anti-collision complex management.
• SIMOPS including construction and well intervention
• After each incident, procedures for shallow section drilling were enhanced.
• The sequence of events were:
  • 0:00 – Skid rig on well.
  • Batch drilled 12 ¼’’ hole section + 9 5/8’’ intermediate casing
  • 08:30 – Cleaned out CP 24’’ with 17 ½’’ BHA to 131m
  • 16:30 – Drilled 12 ¼’’ hole to 286m with 1.15+ SG mud. Heavy losses (67 m3/h)
  • 20:20 – Homogenize mud to 1.12 SG
  • 20:33 – Resume drilling to 296m. Heavy losses (70 m3/h)
  • 21:10 – Spot 10m3 LCM pill. POOH wet.
  • 22:20 – Well swabbing and started to flow. Closed diverter. Started pumping 1.12 SG mud at high flow rate.
  • 23:04 – Pumped kill mud 1.50 SG, followed by sea water at high rate.
  • 00:30 – Flow outside CP. Well out of control. Full rig evacuation.

What Went Wrong?:

The cause of the incident could be listed as follows:

1. Supervision on rig
   • POOH wet (no pump out)
   • Continue with pulling operations, despite swabbing, until well kicked in. Shallow gas procedure not followed
2. Mud weight
   • Inconsistency in MW control and reporting
   • Pack off at 291m interpreted as a (new) loss zone
3. Documentation
   • No comprehensive instructions concerning total loss situation

Corrective Actions and Recommendations:

• Maintain a continuous awareness on shallow gas hazard, even when the shallow gas section has already been penetrated in other wells. This aims at avoiding routine approach hence complacency.
• The standard drilling Instructions should be enriched and reinforced with lessons learnt e.g. Management of Change, the required concentration of KCl for the top hole section, the threshold of heavy losses, hole cleaning procedure for the top hole, responsibility assignment for key personnel, ‘Ready to drill’ checklist.

safety alert number: 262
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/

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