IOGP Well Control Incident Lesson Sharing
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Wellbore flow observed during fishing of completion tubing string

IOGP Well Control Incident Lesson Sharing #23-6

A land-based workover operation was fishing a tubing string on a cased-hole hydraulically-fractured well when underbalanced conditions were experienced and the well began to flow. Initial attempts to bullhead were unsuccessful and led to pipe-light conditions, while other complicating factors made the well control response more complex. The well was ultimately killed through bullheading and was made secure.

The IOGP Wells Expert Committee/Well Control Incident Subcommittee believes that this incident description contains sufficient lessons to be shared with the industry. We further encourage the recipients of this mail to share it further within their organization.

What Went Wrong?:

During a workover operation on a cased hole hydraulically fractured well, a completion tubing string was being fished. From a subsequent fishing run with an overshot assembly after fishing the permanent downhole gauge, top of fish was tagged at ~11,810 ft, washed over 26 ft and some parts recovered following jarring operations. While tripping out of hole the recovered fish - a wash pipe assembly, the annulus was being filled with CaCO3 mud of 1.2 ppg lighter weight than planned due to tanks being rolled. At ~27 stands (1600 ft) from surface, the well was confirmed underbalanced from flow with static pipe and was immediately shut in on the annular. The shut in casing pressure stabilized at 300 psi.

Initial attempts at bullheading failed to establish injection and led to pipe light condition necessitating steps to secure pipe on surface. Subsequent bullheading attempts successfully established injection and well was killed by bullheading. Lack of strippable TIW and IBOP prevented stripping back to bottom, and a mobilized rig assist snubbing unit could not be rigged up due to rotating rubber installed on the workstring. After the well kill, pressure was bled down over 6 cycles to 0 psi and the well flow checked for 30 minutes with no flow.

Corrective Actions and Recommendations:

  1. While pulling out of hole with fish, pump operator had began rolling the tank without permission from well site representative. While not definitive, it is suspected that improper valve configuration likely caused dilution which lowered the fluid density.
  2. Well was being filled with 1.2 ppg lighter fluid weight than planned. The well was being filled in intervals of 5 stds.
  3. Lack of strippable TIW/BOP to enable stripping to bottom and performing a circulation kill.
  4. Use of rotating rubber limiting response options.
  5. Inability to bullhead solids laden fluid loss controlled fluid into the reservoir without fracturing it.

  1. Have strippable TIW/IBOP available for particular well control stacks - take tool joint OD into consideration.
  2. If rotating rubber is being utilized, ensure it is removed prior to prolonged tripping operation.
  3. Risk assess implications of bullheading using solids laden fluid during completions operations.
  4. There shall be reinforcement of field verification and proper checks of fluid density and appropriate transfer pump operations.

safety alert number: 353
IOGP Well Control Incident Lesson Sharing


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