Page 138 - Handbook Of Multiphase Flow Assurance

134 5. Flow restrictions and blockages in operations

December 1980 US North onshore
At an oil sands plant, possible hydrate formation in the compressor second stage discharge
caused piping rupture due to blockage, and a fire.
May 1987 Europe well
A gas condensate well integrity loss during a productivity test led to a blowout, uncontrol-
lable for the previous several years.
3
After many attempts, an intercept well made a connection, and the injected 40 m kill fluid
got lifted by gas and failed to stop the flow.
3
144 m of ice-cold water was then injected from a nearby lake into the well which formed a
hydrate blockage in the blowout well and stopped gas flow after 80 min.
1997 US onshore
In the onshore gas pipeline a blockage was formed on purpose, then allowed to disband
from the pipe and move through the pipe. The estimated peak speed of the hydrate projec-
tile movement through a gas condensate pipeline was in excess of 300 ft/s (Xiao et al., 1998).
The field test was designed with a long straight section of pipe to avoid any impacts on pipe
elbows.
July 1988 Europe offshore topsides condensate line
Normal process of water removal from condensate was altered for equipment maintenance.
A condensate transfer line got plugged.
The line leaked releasing condensate which ignited and led to a loss of platform and 167
lives.
Hydrate was considered among three other causes. Investigation deemed that hydrate did
not contribute to the incident.
August 2012 US North gas purge line
A 4 in. natural gas liquids gas purge line was washed with soapy hot water, then nitrogen
purge was performed to displace water.
A 10 bbl methanol pill was injected on the upstream end, but it was not pushed the length
of the line.
Pipe is undulating because the pipe supports are prone to subsidence due to freeze/thaw
cycles which is common in permafrost areas.
The line looks like a roller coaster with lots of high points and low points that could easily
collect a full diameter of water.
Radiograph inspection confirmed a hydrate plug. Pipe was depressurized in August to
remove hydrate.
Learning: it's not recommended to wash gas lines with water in cold conditions.
April 1997 US North well valve
Hydrate or ice plug formed in a well needle valve during well wireline service preparation.
A heater trunk was suspended from the companion valve to thaw out the needle valve
plug.
After 20 min, operator attempted to open the needle valve again and saw no pressure.
After an additional 5 min, operator opened the needle valve again and some gas began
bleeding off.
Then, suddenly, the hydrate plug released and the gas escaped very rapidly.
The gas hit a slop bucket that the operator was holding and knocked it out of his hand into
the corner of the wellhouse.