Objective
This article aims to address common user questions about the MSE-SRK thermodynamic framework developed by OLI.
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How do I choose between MSE and MSE-SRK?
What happens when there is no second liquid phase in MSE-SRK?
What components can MSE-SRK predict?
Why was MSE-SRK developed?
The MSE-SRK framework extends the Mixed-Solvent Electrolyte (MSE) model by incorporating the Soave-Redlich-Kwong equation of state for the treatment of the gas phase and the 2nd liquid phase. This addition improves the prediction of phase equilibrium for mixtures containing hydrocarbons and/or light gases such as CO₂, H₂S, and N₂, with or without H₂O, over a broad range of temperatures and pressures, including near-critical regions. MSE-SRK is particularly suited for modeling oil & gas production, autoclave applications, and may also be used in refinery and petrochemical processes that involve only hydrocarbons.
Which equations of state are used?
| Phase | AQ Framework | MSE-SRK Framework | MSE Framework |
| Vapor Phase | SRK | SRK | SRK |
| 2nd Liquid Phase | SRK | SRK | MSE |
| Aqueous Phase | Bromley | MSE | MSE |
MSE-SRK can be seen as a bridge between the MSE and AQ models. Like MSE, it leverages the Mixed-Solvent Electrolyte model for the aqueous (liquid-1) phase; this captures most of the benefits of MSE over AQ, as the former is a far superior aqueous model. Like the AQ framework, MSE-SRK leverages the SRK equation of state to model the 2nd liquid phase.
How do I choose between MSE and MSE-SRK?
Please refer to the chart below for guidance.
What happens when there is no second liquid phase in MSE-SRK?
When no 2nd liquid phase is present, MSE-SRK behaves like the standard MSE model. If the 2nd liquid phase is disabled, the software defines the liquid phase as aqueous (liquid-1), and properties are calculated accordingly. However, if the 2nd liquid phase is enabled but only one liquid phase exists, the software will determine whether the phase should be classified as aqueous or as a 2nd liquid.
- Aqueous phase: Properties are calculated using the MSE equation.
- 2nd liquid phase: Properties are calculated using the SRK equation.
The phase classification depends on the amount of water in the system. MSE-SRK is most effective when there are two distinct liquid phases (water and hydrocarbon/light gas).
What is the SRKMSE database?
The MSE-SRK framework is powered by the SRKMSE database. It functions as a “private” database that overrides the corresponding data in the standard MSE database (MSEPUB). SRKMSE is unique because when it is selected, the software will calculate the 2nd liquid phase properties using the SRK equation of state, rather than the MSE equation.
Since MSEPUB is the primary database, it still governs the calculation of the ions, aqueous species (without vapor counterparts), and solid species.
What components can MSE-SRK predict?
MSE-SRK excels at predicting the solubility of water in hydrocarbons and light gases. The SRKMSE database includes several additional components, such as:
- MEG (Monoethylene glycol)
- DEG (Diethylene glycol)
- TEG (Triethylene glycol)
- Formic acid
- Acetic acid
- Methanol
- Mercury
- Sulfur (introduced in Version 11)
This was done by developing SRK interaction parameters for these components in hydrocarbon mixtures. However, these parameters will only provide reliable predictions when small amounts (less than ~10%) are dissolved in the hydrocarbon mixture. Notably, this is often sufficient for the oil and gas production applications for which MSE-SRK is intended.
This FAQ has been crafted to guide users through the essential features of MSE-SRK, helping them to apply the model confidently across various industrial applications. Should you have further questions or require support, OLI's dedicated team is here to assist.