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Asphaltene deposition is a major flow assurance challenge in oil production. Changes in fluid temperature, composition, and particularly pressure, can all lead to solid asphaltene precipitation. This may deposit in the formation, wellbore, or production lines, causing reduced flow or even complete blockage. The objective of this work was to evaluate a recently developed, novel high-pressure high-temperature (HPHT) quartz crystal microbalance (QCM) set-up for the testing of asphaltene deposition inhibitors.Developed within a joint industry project (JIP) aimed at improved asphaltene inhibitor testing and deposition modelling, the variable volume (50 to 450 ml), HPHT QCM set-up can operate at pressures up to 410 bar (6,000 psi, extendable to 690 bar / 10,000 psi), allowing measurements on live oil / re-livened oil (dead oil made live again by gas addition) systems for real production pressure-temperature (PT) conditions / scenarios. In this work, the HPHT set-up has been used to evaluate several commercial asphaltene inhibitors for two re-livened oil systems in terms of AOP pressure and relative mass asphaltenes deposited versus blank (inhibitor-free) cases. For comparison, traditional heptane titration tests were also carried out for the same dead oil ± inhibitor systems using an atmospheric QCM apparatus.Results demonstrate the HPHT QCM to be a very promising tool for asphaltene inhibitor evaluation, with clear variations in anti-deposition performance seen for different chemicals. Furthermore, while findings show that atmospheric pressure dead oil titration results often agree well with those for re-livened HPHT tests, there are significant differences for some inhibitors, meaning the former may not always be representative of real conditions, while the latter should presumably be more so. These observed differences may go some way to explain problematic discrepancies between traditional laboratory test approach results and real-field chemical treatment performance, i.e., where an inhibitor performs well in the laboratory, but not in the field.The reported HPHT QCM approach is novel in that it can be used to investigate asphaltene inhibitor performance for live / re-livened fluids for real production PT conditions/scenarios. |
