Laboratory testing of corrosion inhibitors under high temperature high pressure (HTHP) conditions is challenging. HTHP testing has been traditionally performed in closed systems with fixed liquid/gas volume and testing results are usually influenced/compromised by the accumulation of ferrous ions and corrosion products. The aim of the work is to optimize corrosion inhibitor testing conditions at HTHP to generate results of better reliability. The corrosion of carbon steel by CO2 at HTHP was assessed using small working electrodes of large liquid volume-to-sample surface area in autoclaves. The effect of CO2 partial pressure was also investigated. The blank and inhibited corrosion rates were monitored by linear polarization resistance (LPR) and the morphology of coupon surface was measured by vertical scanning interferometry (VSI). The testing results were deemed to be more representative of the field service environment when the amount of ferrous ions and corrosion products was reduced due to the usage of small working electrodes.
Mitigating oil and gas production with chemical inhibitors is challenging when high temperature (>120°C) and H2S is present. The high temperatures associated with deep wells and thermal recovery methods demand an advancement in conventional inhibitor technologies. Traditional organic inhibitors struggle to protect carbon steel assets lending them susceptible to localized corrosion in sour environments. These environments require inhibitors with a combined thermal stability and persistency to provide uniform filming and corrosion protection.
For high temperature corrosion applications imidazoline chemistry ranks highly as a chemistry likely to be able to mitigate corrosion at elevated temperatures. However, at temperatures between 120 and 150°C performance is very system specific while over 150°C performance can be severely limited. An extensive in-house screening program was undertaken which identified a generic chemistry (pyrimidine) that exhibited the required performance characteristics up to 175°C for a variety of field applications. Based on this work, several other materials exhibited performance benefits for alternate applications, for instance high temperature, deep water applications. Laboratory testing of the novel corrosion inhibitors at high temperatures, also highlighted the limitations of corrosion test methodologies for evaluating inhibitors under extreme conditions.