While drilling ahead in salt on the Pompano A-31 (Gulf of Mexico) wellbore
below the 16-in. shoe, the rotary stalled abruptly, and the drillpipe
simultaneously became stuck. Subsequent calipers indicated the 16-in.
casing to be deformed onto the drillpipe at approximately 250 ft.
To the authors’ knowledge, this situation represents the first instance of
an annular pressure buildup (APB) failure during drilling. APB is
typically associated with extremes of temperature change resulting from
production operations. In the current instance, the temperature change is
solely from circulating drilling fluid.
This paper provides a detailed post-analysis of the 16-in. casing failure as
- An overview of the conventional casing design for this well, indicating
that normal operating conditions should not have resulted in a failure.
- A review of the failure event, substantiated by field measurement and
- An investigation of APB, associated with inadvertently closing the 16-in.
casing annulus at the surface, demonstrating the magnitude of the possible
resulting thermally induced pressure load.
- Consideration of an alternate failure mode, column buckling, to demonstrate
that this failure mode was not active in this wellbore.
- A finite-element model of the drillpipe/16-in. casing/20-in. casing trio
indicating that, in addition to the collapse of the 16-in. casing and
subsequent sticking of the drillstring, the outer 20-in. casing was also
damaged by the event.
The latter item is particularly important because damage to outer strings
can be easily overlooked if concentration is on the collapsed casing and
drillpipe fish. A mechanical caliper confirms damage to the outer 20-in.
Conclusions in the paper center on confirmation of the postulated failure
mode by field measurement and recommendations for avoiding such an event.
While drilling ahead at 9,132 ft. on the Pompano A-31 wellbore (Vioska Knoll
989 A-31, OCS-G-6898) below the 16-in. shoe (Fig. 1), the rotary stalled
abruptly, and the drillpipe simultaneously became stuck. An increase of
mudflow out of the flowline surged over the gumbo buster.
Approximately 500-psi pressure was bled off the 16-in. by 20-in.
annulus. The fluid initially recovered from the 16-in. by 20-in. annulus
was a clear, 10-ppg brine, but later changed to a 10.5-ppg, synthetic-based mud
composition tantamount to the fluid placed above the cement top in the 16-in.
© 2006. Society of Petroleum Engineers
View full textPDF
- Original manuscript received:
4 June 2004
- Manuscript approved:
1 May 2006
- Version of record:
20 December 2006