Confirm that all equipment in the well control circulating path is rated for the application
The tubing was cemented in rotation using a casing drive system (integrated elevator/circulation device connected to top drive). The program called for a slurry displacement with an underbalance brine 1.02SG in order to leave the tubing full of clean fluid for subsequent operations.
The plug was bumped. During the tubing P-test at 7300psi - pressure dropped to 5300psi - 6 bbls were bled off to check floats - no success. Observed pressure build-up indicating link to reservoir (+/- 40psi/hour).
Unfortunately the surface rig-up (casing drive system) was only 5K working pressure (WP) and did not allow slickline access due to a restricted Internal Diameter.
What Went Wrong?:
The casing drive system was not identified as being part of the secondary barrier system at the end of the displacement.
Packing elements of the Casing Drive System were not qualified - only 5K WP for 7.5K MEWHP.
Mechanical barrier failure - shoe track integrity.
Displacement with an underbalance fluid disabled the primary barrier (hydrostatic fluid).
Corrective Actions and Recommendations:
An operational risk assessment of the operation must be performed and "What If" situations evaluated (failure of shoetrack integrity).
Revision of the cement job procedure and landing string design - must incorporate a surface safety valve and possibility to run through a contingent of mechanical barriers.
All the equipment being part of the barriers (primary and secondary) must be qualified to the MEWHP.
Figure 1: Surface set-up
Schematic of the pumping set-up with 5K packing elements (for a 7300psi MEWHP)
safety alert number: 303
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/
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