The impact of thermal ageing on sealing performance of HNBR packing elements in downhole installations in oilfield wellhead applications

Hydrogenated nitrile butyl rubber (HNBR) elastomers are highly resistant to chemicals and degradation, and they are good candidates to be adopted in aggressive environmental conditions of high temperature and pressure. As these service parameters are common in oil and gas applications, HNBR is popular in applications such as elastomer packers in wellhead installations. This study investigated the thermal ageing behaviour of HNBR elastomers to better predict the long-term sealing performance of the packers. Elastomer compounds were thermally aged and FTIR-ATR and differential scanning calorimetry techniques were used to indicate dominant chemical reactions during ageing. Furthermore, the mechanical performance of the aged compounds were studied to investigate the effect of dominant ageing reactions on performance. It was indicated that crosslinking reaction was dominant in the ageing process of HNBR compounds up to 150 °C. This resulted in increased stiffness and alleviated elongational strains at the break. However, compounds behaved brittle at ageing temperatures above 150 °C, and from the thermal analysis, it was concluded that at those temperatures chain scission reactions overtook the ageing mechanism. Finally, an approach for life-long prediction of mechanical characteristics of the specimens showed while long-term ageing promotes elastic failure, ageing temperatures above 150 °C facilitate rupture because of the brittle response of the compounds.