Page 139 - Handbook Of Multiphase Flow Assurance

Hydrate of natural gas 135

A flash fire occurred while the gas was escaping. The flame slightly affected the operator's
hair. Service crew stopped the job and exited the unit.
The flame extinguished itself and no additional gas was escaping. The operator reentered
the wellhouse to shut the needle valve.
The operator was in the appropriate position (out of the line of fire) at the time of incident
and was wearing all appropriate PPE (suit, safety glasses, hardhat, etc.).
Learning: grounding strap should be attached from the slop bucket to the wellhead.
October 2004 Canada underground tank
Water dump valve on inlet separator stuck open and high level shutdown on the water
tank failed causing water and condensate to leave process equipment.
Liquid was contained onsite in bermed area around tank.
Learning: Process problem caused formation of hydrate in water boot, causing valve to
stick and float to malfunction.
November 2009 US North oil line
Operator discovered an oil spill from the line along the pipeline road and instructed fa-
cility controls to conduct an Emergency Shut Down and initiate the Emergency Action Plan.
Two weeks prior, operations lead identified a low temperature condition on one of the two
parallel lines entering the facility.
Operators bled down pressure on both ends of the low temperature line to evaluate flow
conditions.
A rapid drop in pressure at each end indicated the line had ceased flow and had blockages
close to each end.
According to hydrate handling procedures, the facility prepared a temporary line thawing
procedure and staff began conducting a risk assessment of the temporary thawing procedure.
The line failed 3 days later before the risk assessment and the thawing procedure could be
completed.
Line failure was at the 6 o'clock position limiting environmental impact.
Based on temperature monitor analysis, the failed line flow stopped and production di-
verted to the parallel larger line without recognition.
The surface mounted temperature monitor on the pipeline was located inside the enclosed
facility. This condition created an inability to accurately reflect pipeline temperatures due to
process equipment heat.
A solid plug of ice caused the failure.
October 2004 Europe onshore oil line
A hydrate formed in a remote gathering oil line with water cut below 5%, blocking the
flow. The line in marshy area was found ruptured.
After repair and environmental cleanup the production resumed with methanol inhibition.
Methanol was later replaced with hot water to keep fluids outside of hydrate conditions.
January 2009 Africa offshore flowline
During a production restart following a week-long shut down, operator noticed a higher
than usual riser base pressure.
Operator shut the system back down, believing that there could be a blockage forming in
the riser.
Initial analysis concluded that the riser was not blocked, but high pressure was caused by
large quantities of liquid accumulated in the flow line during the shutdown.