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Ejection of workstring during bull-heading operations

The rig was involved in well preparation for the forthcoming execution of a gravel pack operation. After earlier setting a Gravel Pack packer on the well, later it became impossible to circulate in direct (possibly plugged ports in string): only possible to circulate in reverse. This made Gravel Pack operation impossible. Decision was made to POOH wet to surface.

The ongoing operation at time of event was POOH with 4 ½ PH6 tubing work string – with Setting Tool and 2 3/8” tubing tail pipe - to inspect Service Tool for indications of inability to circulate.

• Fluid in well was 1.07sg Brine.
• Tubing string was being pulled wet.
• Losses observed at approximately 1.2m³/hr.
• Tubing work string was 220m from surface at time of incident. Fluid returns were bubbling at the bell nipple (swabbing while pooh workstring-no gain yet). Crew estimated off-bottom kick situation. Closed annular to bullhead the well to push any gas influx into formation.

Operations details after calling town (drilling superintendent):

1. Pump 5m³ High Viscosity pill bullheading same at a flow rate not exceeding 800 lpm and at a stand pipe pressure not exceeding 1400 psi.
2. Pumps were stopped and lined up with active pit, then approximately 7m3 1.07 sg brine was bullheaded. First, the flow rate was maintained around 400 lpm and stand pipe pressure remained below 1500 psi.
3. Increased gradually the flow rate (to 1100 lpm) and the stand pipe pressure increased regularly up to 2300 psi.
4. The Tool pusher called the driller to ask him why he was pumping at a stand pipe pressure higher than 2000 psi – the driller replied the Company Man told him 2500 psi was the limit.
5. 220m+/- of 4 ½” tubing and 2 7/8” wash pipes along with the Service Tool Assembly were ejected from the well. Strong noise and vibrations were noted by several witnesses while the pipe was being ejected.
6. The pipe hit the Elevator and was deviated outside the mast, hitting the monkey board and went up over the Monkey Board and out through the derrick space.
7. The projectile started to drop down in an X-shape. It eventually fell on the ground, missing the company man’s and the service companies’ cabins by less than 1 meter,
8. The Rig HSE/Meeting Room Cabin was destroyed.
9. Damage was made to the concrete block fence wall inside the cluster situated just behind the Company Man Office.
10. From Company Man Office to Well Center the Tubing string landing point was measured at 60m.
11. The elapsed time of the entire event according to witnesses, took less than 30 sec (faster than a man running down the stairs from the rig floor).
12. Driller remained on Rig Floor during ejection. He immediately stopped the rig pumps then went to the BOP panel. He did not close the pipe rams as he had little hope this would be of any help. He decided to close the Blind Shear Rams. Then he left the rig floor and went to the main muster point.
13. The Company Man and Tool Pusher both ran to the remote control panel. The Tool Pusher arrived first and activated the Blind Shear Rams, then realized that the driller had already done it.
14. All personnel proceeded to the Muster Points.

    
    Immediately after the incident:

15. The Head Count was 100% - no one had been injured.
16. The Driller went back to the Rig Floor and resumed the Bullheading Operation against the Blind Shear Rams.
17. The day after the incident (Saturday 9 November).
18. A piece of tubular was found at 105m from the well outside the cluster.

What Went Wrong?:

1. Gravel Pack string was plugged creating inability to circulate direct and thus to execute the Gravel Pack program.
2. According to witnesses, squeeze pressure range was given by Company man to the Driller as 2000 – 2500 psi.
3. No formal risk assessment performed for Bull Heading operation for this Work-over operation.
4. No recalculation was done for this emergency non-routine Bull Heading well control operation either on site or at base by Company and Drilling Contractor.
5. Nobody on site neither in office recognized Well Control situation as critical.
6. Top drive was disconnected and drill pipe closed on TIW valve. 220m assembly closed on annular.
7. The Tripping Fast Shut In Procedure does not mention pipe rams closure.
8. There is no Bull Heading procedure available.

Corrective Actions and Recommendations:

1. Lack of risk awareness concerning contained Pressure hazards. Upward push on the assembly while bullheading not anticipated despite gravel pack operations experience on site.
2. No Job risk Analysis performed prior bullheading. No consequential analysis
3. Bullheading operation considered as routine.
4. Due to underestimation of the criticality of the operation ongoing (Bull Heading) by all (site and base) : Identify all critical operations/tasks including Bull Heading in drilling operations.
5. Prioritize Well Control and Critical Operations by base team at every point of Program execution.
6. Dedicated ‘critical activities’ section to be added in all operational programs (drilling, Workover, rig less) describing how to recognize a well control situation and which procedure to be applied. Each procedure completed by a Risk Assessment made available to the work crew which they can use as a basis for further review.
7. Training plan to be immediately set up for full IWCF compliance of the Completion and Well Intervention personnel.

safety alert number: 264
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/

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