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But function isn’t the only difference between
transmission and gathering lines. Transmission lines
are quite large: they typically measure between 12
and 56 inches in diameter. Many cross hundreds
of kilometers of public land and can run very close
to densely populated “high-consequence areas”
(HCAs), so they tend to be subject to some form
of government or industry regulations. As a result,
some (but not all) aging transmission lines tend to
be better maintained and less prone to failure.
Gathering lines, on the other hand, are typically
located in more remote areas with very low
populations, which is one reason that many of them
have not been regulated.
The result: Oil and natural gas
fields worldwide are home to
decades-old gathering lines that
do not have the same integrity
management process applied
to transmission pipelines.
And as these lines age, the
risk of failure is becoming
a reality.
“A Finite Life”
“Gathering systems – by
nature of their design and the
wells they serve – have a finite life;
transmission systems can be rerouted
or reversed and used for different things,”
says Mike Kirkwood, Ph.D., a transmission market
and integrity expert for global pipeline services
provider T.D. Williamson (TDW).
The world’s first generation of gathering lines
was built on the assumption that oil wells, too, had
a finite life. And, 30, 40, or even 50 years ago, that
was true: After a decade or so, the well would stop
producing. But today, operators can use cutting-edge
technology to reach deeper, less-accessible reserves.
Wells – and the accompanying gathering lines – are
living longer.
This wouldn’t be a problem if gathering lines
could be cleaned, tested, and maintained like
transmission lines. Hydrotesting is not a good
option because of the lack of access to water
and the higher pressure required. In the case of
gas, drying the lines can be problematic. What’s
more, gathering lines are often too small and close
together to be pigged.
“If you look at old systems, the gathering lines are
like spaghetti,” says Kirkwood. “They’re very hard
to access. Even if you wanted to get tools into these
lines, there’s no space to do it.”
The Future of Gathering Line Integrity
The Nefteyugansk leak highlights a widespread
problem: As the world’s population grows and
cities sprawl out in new directions, many old
gathering lines are now located precariously
close to HCAs. As a result, many countries are
looking into ways to regulate them like
transmission lines. This makes the
need for solutions even more
pressing.
In February 2014, Dr. Ali
N. Moosavi, of Abu Dhabi
Company for Onshore
Oil Operatons (ADCO),
gave a presentation called
“Integrity Assurance of
Unpiggable Pipelines” at the
7th Annual Pipeline Integrity
Management (PIM) Forum in
Berlin, Germany.
Like Russia, the Middle
East has been struggling in recent
years with a combination of increased oil
production and rapidly deteriorating infrastructure.
Moosavi’s presentation provided a look at some
current solutions and best practices used to combat
corrosion and prevent further damage on aging
gathering lines.
The overall message: It’s not easy, but it’s
possible.
One option is a modified pigging program that
eliminates the need for a pig launcher and instead
uses cables and winches to pull the pig through
the line; another option is to install piggable valves
or piggable “Y” bypasses. This option can make
cleaning and inspection a reality. It is also possible
to install durable, corrosion-proof plastic liners
in existing gathering lines, which extends their
lifetimes considerably.
And, of course, there’s always the option to