Asphaltene is termed as “cholesterol of petroleum” since it can precipitate during production, transportation, refining and processing of crude oil and stops the entire production causes the loss of millions of dollars. It is an “ill-defined” component of high molecular weight ( around 1000-4000 gm/mol), which is considered the most polar part in the oil. This polar nature of asphaltene is imparted by heteroatoms (O, S, N, vanadium, nickel) present in its polynuclear structure. Because of this polar nature, asphaltenes associate with each other and precipitate at certain temperature, pressure and composition. However, prediction of these conditions, where asphaltene precipitates, is quite uncertain and detailed thermodynamic model is required. Asphaltenes can easily precipitates as pressure is reduced but also if the oil is diluted with light hydrocarbons eg. gas such as methane, carbon dioxide or nitrogen. Ever since the introduction of enhanced oil recovery (EOR) method with gas this problem has become even worse.
There have been many studies done on the asphaltene modelling, based on colloidal theory and true solution approach. Since the invention of association models in 1990s, many people tried to apply SAFT, AEOS and CPA, which is based on Wertheim theory, for asphaltene modelling. There are several variants, some of which only use the improved (over cubic equation of state) dispersion and chain term of SAFT, while others use the full version of SAFT including association term. Existing research with association models show the promising correlations between model results and experimental data. Different hypothesis have been studied to understand the mechanism of asphaltene aggregation with resins and its deposition. However, the actual characteristic of asphaltene is still unknown and research outputs are still not convincing to many industries, which entails additional research on this topic. Moreover, research with CPA is limited compared to SAFT.
In this PhD project we aim to apply association models, CPA and PC-SAFT equation of state, to asphaltene systems and complete the following objectives.
- Modelling strategy of asphaltene precipitation using CPA and comparison of results with experimental data.
- Modelling strategy of asphaltene precipitation using PC-SAFT and comparison of results with experimental data.
- Comparison between CPA and PC-SAFT with respect to asphaltene modelling.
- Adding these modelling strategies to ThermoSystem, CERE inbuilt software for thermodynamic modelling with CPA and PC-SAFT, for its potential use in industries.
Supervisor: Prof. Georgios Kontogeorgis, gk@kt.dtu.dk
Co-supervisor: Assoc. Prof. Nicolas von Solms, nvs@kt.dtu.dk