22 EUROPEAN RUBBER JOURNAL • September/October 2016

oilfield applications

Meeting toughnew requirementson elastomers inoilfield applications

collaboration is key to developing elastomer materials that meet the increasingly demanding requirements of oilfield application, writes paul Ruscoe of Zeon europe

Recovering crude oil from the depths of the earth is becoming more challeng-ing: environmental stand-ards, 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, high-er pressures and resist more severe chemical environments, while also ensuring the quality, efficien-cy and longevity of vital produc-tion components.

The selection of elastomers and correct formulation has, therefore, become more demanding in re-cent years: presenting increasingly complex issues. This is evidenced by a trend towards project-specific developments and closer collabo-ration between materials suppliers and oil & gas companies.

Materials have to be closely

adapted to the different drilling locations and its specific condi-tions. Careful choice of elastomer and correct compound design are essential to ensuring that compo-nents add long-term value to pro-cesses for recovering these costly energy resources.

High resistanceAll elastomers used in the oil-field industry must provide high resistance to oils, drilling muds and various aggressive produc-tion 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 mi-nus 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 sub-jected to extremely high-pressure loads. In some high-pressure, high

temperature (HPHT) applications, pressures of over 260 MPa can be seen. To combine heat resist-ance with high strength and good chemical resistance is a real chal-lenge.

Elastomer compounds have to be strong enough to take the impact during handling, instal-lation and operation. If a sealing lip wears away or has been dam-aged by rapid gas decompression (RGD), potential for leakage arises.

Moreover, if the elastomer part of a stator (elastomer lobes) gradu-ally wears away, pumping efficien-cy can drop. Or if the heat build-up 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 chemi-cal-resistant then hardening, em-brittlement, and severe set can take place, leading to failure of of-ten critical parts, such as seals.

In oilfield service, elastomeric materials play major roles in pro-tecting workers, equipment, and the environment, and replacing

paul Ruscoe is Zetpol HnBR technical service manager at Zeon chemicals europe

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24 EUROPEAN RUBBER JOURNAL • September/October 2016

oilfield applications

components during operation is a time-consuming and expensive task.

Among the key high-end mate-rials 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 typ-ically include hose, stators, pack-ers, seals, and blow-out preventers.

At the very top end are compos-ites based on a proprietary mod-ification of HNBR. These highly heat-resistant elastomeric alloys can deliver huge improvements in tensile strength, abrasion resist-ance and dynamic properties.

Ultra-high strengthThese polymers offer ultra-high tensile strength – up to around 50MPa – as well as exception-al RGD resistance, making them suitable for highly demanding oil & gas applications. They are typi-cally blended with standard HNBR polymers to balance certain prop-erty requirements, such as chemi-cal resistance and compression set.

Zeon has developed a number

of these advanced compounds, which have been tested and certi-fied to the Norsok M710 industry standard for RGD resistance.

Some of these modified HNBR materials have excellent low-tem-perature properties, as well as high tensile and tear strength required to pass the Norsok M710 RGD requirements. They also have ex-cellent fatigue and dynamic prop-erties, as required for applications such as stators.

new testing The use of advanced oil & gas elasto-mers is increasingly being support-ed by high-pressure test equipment that allows testing of compounds in commonly encountered oilfield flu-ids at high temperatures and high pressures. This capability generates valuable test data that guides tech-nologists in the selection of materi-als for use in the design of elastomer compounds.

Many different ingredients are used in the compounding of elas-tomers and this combination of ingredients give the final product improved performance character-istics. This data is particularly crit-ical in the development process when optimising compounds for oil & gas applications.

For larger studies, design of ex-periments (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 ingre-dient 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 impor-tance in high-pressure sealing ap-plications, especially when space limits the use of supporting metal back-up rings.

Other R&D work at Zeon includes the study of low-friction com-pounds for dynamic applications and the development of novel low compression set HNBR polymers that exhibit exceptional long-term compression set resistance.

predictabilityResearch into maintaining phys-ical 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 im-proving the understanding of failure modes in elastomer com-pounds 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 projectIn one specific project for the oilfield industry, Zeon was heavily involved in the compound development for elas-tomer packers. The challenge was to achieve an elastomer compound with very high hardness (around 90 Shore A) that had good elongation and hightear strength at elevated applicationtemperatures.

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 opti-mised other properties can fall out of

specification. Finally, the manufacturing and

processing properties of the elasto-mer compound had to be optimised. The final compound met all the re-quirements using a blend of polymers

and fillers in conjunction with an ef-fective 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 be-tween materials supplier and custom-er 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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