Download Meeting tough new requirements on elastomers in oilfield applications

oilfield applications
Meeting tough
new requirements
on elastomers in
oilfield applications
Collaboration is key to developing elastomer materials
that meet the increasingly demanding requirements of
oilfield application, writes Paul Ruscoe of Zeon Europe
R
Paul Ruscoe is
Zetpol HNBR
technical
service
manager
at Zeon
Chemicals
Europe
22
ecovering crude oil from
the depths of the earth is
becoming more challenging: environmental standards, sustainability issues,
and difficult-to-reach oilfields are
making drilling more technically
demanding.
In oil & gas exploration and
production, elastomers perform a
host of critical functions topside
and downhole, where demands
on the polymeric materials are
continually increasing.
They must, for example, allow
for increasing temperatures, higher pressures and resist more severe
chemical environments, while
also ensuring the quality, efficiency and longevity of vital production components.
The selection of elastomers and
correct formulation has, therefore,
become more demanding in recent years: presenting increasingly
complex issues. This is evidenced
by a trend towards project-specific
developments and closer collaboration between materials suppliers
and oil & gas companies.
Materials have to be closely
adapted to the different drilling
locations and its specific conditions. Careful choice of elastomer
and correct compound design are
essential to ensuring that components add long-term value to processes for recovering these costly
energy resources.
High resistance
All elastomers used in the oilfield industry must provide high
resistance to oils, drilling muds
and various aggressive production fluids.
Compounds also need to exhibit
a range of outstanding properties,
including high tensile strength,
excellent dynamic properties, good
abrasion resistance, high heat &
chemical resistance, and operate
over a wide temperature range.
Possible applications range from
Arctic temperatures down to minus 60°C up to temperatures of
over 250°C.
In addition to their ability to
withstand extremes of cold and
heat, materials are often also subjected to extremely high-pressure
loads. In some high-pressure, high
temperature (HPHT) applications,
pressures of over 260 MPa can
be seen. To combine heat resistance with high strength and good
chemical resistance is a real challenge.
Elastomer compounds have
to be strong enough to take the
impact during handling, installation and operation. If a sealing
lip wears away or has been damaged by rapid gas decompression
(RGD), potential for leakage arises.
Moreover, if the elastomer part
of a stator (elastomer lobes) gradually wears away, pumping efficiency can drop. Or if the heat buildup in the rubber lobes increases
too much, due to internal friction,
then severe premature failure of
the stator can occur.
Furthermore, if elastomers are
not sufficiently heat- and chemical-resistant then hardening, embrittlement, and severe set can
take place, leading to failure of often critical parts, such as seals.
In oilfield service, elastomeric
materials play major roles in protecting workers, equipment, and
the environment, and replacing
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oilfield applications
components during operation is
a time-consuming and expensive
task.
Among the key high-end materials in this space is hydrogenated
nitrile butadiene rubber (HNBR)
and its compounds, which are used
in applications requiring excellent
balance of high strength, heat and
fluid resistance. End-products typically include hose, stators, packers, seals, and blow-out preventers.
At the very top end are composites based on a proprietary modification of HNBR. These highly
heat-resistant elastomeric alloys
can deliver huge improvements
in tensile strength, abrasion resistance and dynamic properties.
Ultra-high strength
These polymers offer ultra-high
tensile strength – up to around
50MPa – as well as exceptional RGD resistance, making them
suitable for highly demanding oil
& gas applications. They are typically blended with standard HNBR
polymers to balance certain property requirements, such as chemical resistance and compression set.
Zeon has developed a number
of these advanced compounds,
which have been tested and certified to the Norsok M710 industry
standard for RGD resistance.
Some of these modified HNBR
materials have excellent low-temperature properties, as well as high
tensile and tear strength required
to pass the Norsok M710 RGD
requirements. They also have excellent fatigue and dynamic properties, as required for applications
such as stators.
New testing
The use of advanced oil & gas elastomers is increasingly being supported by high-pressure test equipment
that allows testing of compounds in
commonly encountered oilfield fluids at high temperatures and high
pressures. This capability generates
valuable test data that guides technologists in the selection of materials for use in the design of elastomer
compounds.
Many different ingredients are
used in the compounding of elastomers and this combination of
ingredients give the final product
improved performance characteristics. This data is particularly critical in the development process
when optimising compounds for
oil & gas applications.
For larger studies, design of experiments (DOE) software can be
used to understand and predict the
effect of not only the ingredients
used in the compound but also the
effect of the amount of each ingredient used. DOE software can be a
very useful tool for larger projects,
which can save time and reduce
the amount of iterations that are
common in traditional compound
design.
Another important part of the
toolkit is API extrusion resistance
test equipment, which is used to
test the extrusion behaviour of
elastomer compounds at elevated
temperatures and pressures. These
properties are of primary importance in high-pressure sealing applications, especially when space
limits the use of supporting metal
back-up rings.
Other R&D work at Zeon includes
the study of low-friction compounds for dynamic applications
and the development of novel low
compression set HNBR polymers
that exhibit exceptional long-term
compression set resistance.
Predictability
Research into maintaining physical properties, such as hardness,
modulus and tensile strength, over
a wide temperature range is also
being studied in order to improve
the predictability of elastomers
under various service conditions.
Also, a large study is underway to
understand further the effects of
H2S (hydrogen sulphide) ageing
on elastomers.
These studies are aimed at improving the understanding of
failure modes in elastomer compounds in addition to pushing
the performance window of HNBR
and other elastomer compounds.
The goal is to provide improved
elastomer performance, efficiency
and longevity in a multitude of
oilfield applications.
Collaboration proves key to oil-drilling project
In one specific project for the oilfield
industry, Zeon was heavily involved in
the compound development for elastomer packers. The challenge was to
achieve an elastomer compound with
very high hardness (around 90 Shore
A) that had good elongation and high
tear strength at elevated application
temperatures.
In addition, good compression set
resistance was required for improved
long-term sealing properties and to
allow for the easy retrieval of the
packer from downhole after service.
The balance of achieving all of these
properties is very difficult due to the
fact that when one property is optimised other properties can fall out of
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specification.
Finally, the manufacturing and
processing properties of the elastomer compound had to be optimised.
The final compound met all the requirements using a blend of polymers
and fillers in conjunction with an effective and appropriate cure system.
With close cooperation and with
a good, open relationship with the
end customer and the manufacturer
a compound was developed, tested,
successfully processed and is now in
use downhole.
Full details of the project cannot be
disclosed due to confidentiality, but
this is an example of engagement between materials supplier and customer and supply-chain assisting where
possible, through every aspect of
the project, from polymer selection,
compound development and testing,
right through to final manufacturing
optimisation.
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