Page 21 - Handbook Of Multiphase Flow Assurance

Why flow assurance failures happen 15

Knowledge required in flow assurance

It is not sufficient to just analyze the flow of fluids, but one must also recognize and
predict the temperature and phase transitions as vapor, liquid and solid phases appear at
different temperatures and pressures. Therefore, a flow assurance engineer must first be
prepared in measuring and calculating fluid properties and phase equilibria, which is com-
monly taught in chemical engineering, heat transfer, which is taught in mechanical engi-
neering, or chemical engineering, and oilfield process equipment operation which is taught
in petroleum engineering, as well as a range of other disciplines such as materials science,
biochemistry, chemistry.
It is not possible to get trained in all these specialties at once, so a flow assurance knowl-
edge is acquired over time. Flow assurance is a relatively young discipline and only a few
universities recently started to teach flow assurance.
It is not enough to be skillful in setting up a multiphase flow model, but it is important
to understand what can happen to the fluids as they flow from the reservoir to the refinery.
Equally, it is not sufficient to know how to set up a scale or asphaltene precipitation model,
but necessary to understand the underlying lab work and what eventualities may lead to a
change in the steady operating conditions and to design chemical injection program with
such eventualities taken into account.

Why flow assurance failures happen

Two main reasons which explain the majority of flow assurance related incidents are: in-
complete understanding of fluid properties and exceeding the safe operating limits. The first
usually happens from lack of training or experience. The second may happen either due to
an operator error or from operator's inability to explain to the management how exceeding
the designed operating conditions will lead to a failure. Management may be motivated by a
short-term incentive to reach a certain production target and request production operations
to exceed the pre-determined limits; such operational deviations done without proper labo-
ratory evaluations and technical plan seldom result in sustained improvement but can often
lead to production interruptions followed by downtime, costly remediation and/or loss of
confidence.
A typical subsea blockage related to flow assurance may cause several months downtime
plus cost upwards of $15 million, as of the writing of this book, to hire a technology for clear-
ing it if remediation program is successfully implemented, or lead to an even costlier well
workover, flowline replacement or well abandonment if remediation is unsuccessful. In ex-
treme cases, flow assurance failure may lead to contractual sanctions stemming from inability
to deliver produced oil or gas, which cost may escalate into hundreds of millions of dollars,
or to a complete loss of license to operate in a given country. Usually gas hydrate or paraffin
wax blockages may lead to such extreme cases.
In the most extreme cases, blockages may lead to casualties. In an onshore field, a hydrate
blockage driven by pressure differential moved inside a pipeline, ruptured the pipe bend
and hit an operator. In the Piper Alpha offshore platform, a hydrate blockage in a condensate