MEC&F Expert Engineers : OIL PLATFORM ACCIDENT INVESTIGATION – OVER-PRESSURIZATION OF THE WELL ANNULUS

Saturday, November 22, 2014

OIL PLATFORM ACCIDENT INVESTIGATION – OVER-PRESSURIZATION OF THE WELL ANNULUS



OIL PLATFORM ACCIDENT INVESTIGATION – OVER-PRESSURIZATION OF THE WELL ANNULUS



On August 17, 2014, an incident occurred that resulted in significant damage to the lower annular. This was an exploratory drilling operation.  The lower annular operating chamber was prepared for pressure testing on the surface. The target pressure for this test was 3000 psi. Once the lower annular was prepared, the Subsea Engineer started applying pressure to the operating chamber using a test pump. At this time, with the pump still running the Subsea Engineer decided to put away some tools, leaving the test pump unit unmanned. 

The Subsea Supervisor arrived at the test unit to find the test pump unattended. He then left the testing area to look for the other Subsea Engineer. He found the Subsea Engineer in their shop and informed him that the test pump should never be left unattended. The Task Based Risk Assessment did not address the monitoring of the running pump. The Subsea Supervisor also informed the crew they should be testing the upper annular operating chamber and not the lower annular operating chamber. 

At this time a loud bang was heard coming from the testing area and the test pump was then immediately shut down. Further investigation by rig personnel found that the lower annular operating chamber that has a (MAWP) Maximum Allowable Working Pressure of 3000 psi, was overpressurized to at least 10,000 psi.



LIST THE PROBABLE CAUSE(S) OF ACCIDENT:
1)    Poor communication between all personnel involved in the testing procedure.
2)    Leaving the test pump running while unattended allowing the component being tested to over pressurize.
3)    Nothing notated in the Task Based Risk Assessment about leaving the test pump running without properly trained personnel monitoring the pressure.
4)    The Subsea Supervisor failed to secure the test pump prior addressing the Subsea Engineer about leaving pump running and unattended.

LIST THE CONTRIBUTING CAUSE(S) OF ACCIDENT:
1)    Miscommunication and not being focused on the task at hand.
2)    Initial documentation showed the upper annular operating chamber should have been tested and not the lower annular operating chamber.
3)   Not double-checking with Subsea Supervisor prior to commencing testing.

DAMAGED PROPERTY
Lower Annular

COST OF DAMAGE
Sheared inner cylinder studs. Pusher plate blown out of annular housing.  Broken shuttle valve on choke isolation valve.  Also support ring and inner piston dislodged due to over pressurization causing significant damage to lower annular.

Sevan Drilling has been forced to halt operations on a well being drilled in the Gulf of Mexico due to a technical glitch with newbuild cylindrical rig Sevan Louisiana.