afety Alerts
Notice No. 18
February
18, 2005
WELL-CONTROL EQUIPMENT CIRCUMVENTION
An operator experienced a loss of well control while performing a
workover/completion operation. During the operation, completion fluid
pumping was shut off so that a tubing hanger lockdown pin could be
removed from the wellhead to allow visual alignment of the tubing
hanger. Removal of the pin circumvented the blowout prevention
well-control equipment. The well began to flow through the lockdown pin
opening. The driller closed the annular preventer, but this increased
the flowing pressure out of the 1.5-inch opening, preventing rethreading
of the pin back into the tubing hanger.
The well progressively flowed completion fluid (seawater) and then a
mixture of seawater and hydrocarbons out of the opening. Up to three
barrels of crude oil sprayed onto grating, decking, and walls in the
wellbay, with an estimated three gallons spilling into the Pacific
Ocean. Natural gas was discharged in the general direction of the flare
boom, increasing the potential for ignition. Platform personnel
manually shut down operations and activated the deluge system. The
flare, which continued to burn residual system process gas after the
platform shutdown, was eventually extinguished with dry chemical
extinguishers, preventing potential ignition of the gas plume by the
flare. Rig pumps were used to pump seawater into the well through the
kill line on the blowout preventer stack until the flow rate through the
lockdown pin opening decreased enough to allow installation of a valve
assembly; the valve was then closed, stopping the flow from the well.
An MMS investigation of the incident identified two direct causes and
four possible contributing causes:
Direct causes
-
The rig personnel stopped pumping
completion fluids into the well which caused an imbalance in the
hydrostatic pressure against the Monterey Formation, allowing the well
fluids to migrate up through the piping to the wellhead on the
platform.
-
The tubing hanger lockdown pin was
completely removed from the wellhead assembly. Removal of this pin
circumvented the blowout preventer system and provided an exit point
for the wellbore fluids.
Potential causes
-
The operator and its contractors did not
adhere to the MMS-approved Application for Permit to Modify (form
MMS-124) and field rules. This allowed conditions to develop that
were conducive to well-control problems.
-
Inadequate and/or inappropriate training
with respect to performing the inherently unsafe operation of removing
the lockdown pin may have contributed to the incident.
-
The well was not closely monitored for
flow or fluid level during the split tubing hanger landing operation.
A lack of immediate appropriate action by the rig crew may have
resulted from this inattentiveness to developing well conditions.
-
The operator relied upon their
contractors’ extensive experience to perform the job correctly.
However, the operator provided inadequate supervision to the
contractors. In addition, the operator and contractors failed to
complete a Job Safety Analysis for this operation.
Therefore, MMS recommends that:
-
Lessees and operators develop specific
procedures or revise existing procedures for landing dual string
tubing hangers so that circumvention of the well-control system is
eliminated.
-
Well-control training and safety meetings
cover potential consequences of well-control system circumvention.
-
Operators review and/or provide detailed
work procedures to be used by company and contract employees.
-
Rig crews and third-party personnel be
instructed to conform to approved Applications for Permit to Modify
and field rules.
-
Job Safety Analyses be conducted for all
tasks involving potential hazards.
This Safety
Alert can be found on our Website
at:
http://www.mms.gov/omm/pacific/offshore/safety/satoc.htm
