New Features in VMGSim’s PIONA Characterization

Herbert Loria - VMG Calgary


VMGSim 9.5 introduces new features and options in the PIONA Slate environment and Oil Source unit operation that are part of VMGSims's structure oriented characterization system based on PIONA (Paraffins, Iso-Paraffins, Olefins, Naphthenes and Aromatics) components. The new developments include a revamped user interface of the Oil Source unit operation, support for new types of analysis such as SARA (Saturates, Aromatics, Resins and Asphaltenes) distribution, characterization based on Asphaltene Precipitation variables and new settings to speed up regression time.



The first notable change for the PIONA Slate environment can be found in the Input frame, a new variable called Define Slate By was added to set the property a user wants to use to define the initial and final point of a slate, now the initial and final points can be defined by Boiling Point (BP) (old option), Molecular Weight (MW) or Carbon Number (Cn).


If Boiling Point (BP) is selected in Define Slate By box, then the initial boiling point (IBP) and end boiling point (EBP) from distillation curve data must be provided to represent the extreme points of the characterization.

When Carbon Number (Cn) is selected, the Starting Cn and Final Cn that are provided are used to define the boundaries of the PIONA slate.


If Molecular Weight (MW) is selected, then the Starting MW and Final MW are used to define the extreme values of the PIONA slate.


Note that the final extreme point of the PIONA Slate can be defined by different feed types for each one of the defined options. Depending on the property the end points of the feed types are:



Final Cn

Final MW





Light Gas Oil




Middle Distillate




Heavy Gas Oil




Atmospheric Residue




Vacuum Residue




Two new check boxes have also been added to the Input frame: HAP’s Slate and Asphaltene Precipitation.


HAP's Slate

This check box is to be used for environmental applications and when Hazardous Air Pollutants (HAP) pure components are present in the component list. This option will instruct the characterization to create PIONA Slate compounds that have similar carbon numbers than the installed HAP's pure components.

For example; if Ethylbenzene (C8) is defined in the component list, then the PIONA Slate will create an Aromatic C8 compound to take into account any other Aromatic HAP compound with 8 carbons.

Asphaltene Precipitation

This option is to be used for Asphaltene Precipitation applications. This check box instructs the characterization to include extra heavy Dehydrated Aromatic compounds that will behave as resin or asphaltene components when modeling Asphaltene precipitation with solvents.

Pseudo Components Name Mode


A new option was added for naming the PIONA pseudo components: Cn Groups. If this option is active then the pseudo component names will reflect in their name the Cn range that they represent, for example: HC_Paraffin_C8-C12.

Oil Source

This section will go through the new experimental variables, laboratory analyses and settings included in the Oil Source unit operation from VMGSim 9.5.



The first noticeable change in the Oil Source interface is the addition of the Application variable. Depending on the selected application type different options will be available for the experimental variables, laboratory analyses and settings. Relevant properties and analysis are considered for each type of application.


Tight Fluids

This application type is useful to model gas and liquids from tight hydrocarbon resource plays. These fluids are commonly described by extended hydrocarbon analyses that can be complemented with other physical properties like molecular weight, liquid density and saturation pressure. The laboratory analyses and experimental variables considered in this application are:



Oil / Refinery

This application type can be used to characterize crude oils and petroleum fraction assays that represent feeds or products for refinery processes. This option is very flexible since it can be employed to characterize from light to heavy hydrocarbons by making use of their compositional information and physical properties. Laboratory analyses and experimental variables considered for this application type are:


This option is aimed for modeling asphaltene precipitation experiments; here a heavy oil or bitumen is defined by its SARA analysis and the asphaltene yield at different oil / solvent ratios can be used to regress the Oil Source parameters to match the experimental data. The use of the SARA Regular Solution property package is highly recommended when selecting this application type. The laboratory analyses and experimental variables used here are:




Laboratory Analyses

Light Ends Analysis

In this tab the lights ends information can be entered. Light ends are pure hydrocarbons that may have been analyzed separately from the distillation curve assay, or they may have been indirectly measured by the resulting distillation temperature from the batch distillation experiment.


The light ends calculation can be performed based on three different modes:

Specify – This mode uses the provided light ends composition to specify the composition slate.

Auto Calculate – In this mode the composition as well as which light end compounds are necessary to describe the distillation curve will be internally calculated by the Oil Source unit operation.

Match - Normalizes the provided light ends composition to match the lower boiling point fraction of the distillation curve.

PIONA / SARA Distribution

The PIONA Analysis has been moved to a new tab called Distributions that also contains the new SARA distribution added in VMGSim 9.5.


PIONA Analysis

The PIONA Analysis frame has no relevant changes with respect to previous versions, but a new plot has been added to show the PIONA Distribution through the average boiling point, carbon numbers or molecular weight cuts of the composition slate, this cuts are set internally by the Oil Source and cover the whole range of boiling points, carbon number and molecular weight for which the slate’s composition is more than zero.


SARA Analysis

The SARA Distribution is calculated from internal equations based on public data that correlate PIONA distributions and bulk properties to SARA fractions. The SARA individual fractions can also be activated to be used as experimental variables participating in the Oil Source regression.


Atomic Inclusion

The Atomic inclusion variables were moved from the Summary tab to their own tab. This tab allows setting heteroatoms mass or mole contents. Once a mass or mole atomic content is added, the composition of the slate is re-calculated to match the specified value based on the heteroatoms distribution settings. The plot in this tab gives an idea on how a specific heteroatom is distributed through the component slate.


Cn Analysis

The tab containing the Carbon Number (Cn) Analysis has been reorganized, the Cn Analysis frame contains Bulk and Cn + Properties that can be used as experimental variables for regression, these variables used to be located in the Summary tab. A future newsletter will go through details of this analysis type and present an example.


PIONA Compositional Analysis

This tab only had some minor changes for better organization. A future newsletter will go through details of this analysis and show an example.


Asphaltene Precipitation

The Asphaltene Precipitation analysis can be performed when the Application type is Deasphalting, this will bring up a new tab named Asphaltene Precipitation.


This tab can be used to enter asphaltene precipitation experimental data to be regressed within this unit operation. In order to model asphaltene precipitation using the PIONA characterization, the user first has to create a PIONA Slate that has enough dehydrated aromatics to represent asphaltenes and resins, to do this go to the PIONA Slate environment and check the Asphaltene Precipitation box that enables the calculation of an extended list of dehydrated aromatic components, also the Asph. Precip. Settings box inside the Range Settings should be checked. Once this is done, the slate can be created by clicking on the Create Slate button.


In order to ensure the best results for Asphaltene precipitation it is highly recommended to use the SARA Regular Solution Property Package, this property package has a proven record for estimating the correct amounts of asphaltene precipitated with solvents ranging from C3 to C16.

A more detailed explanation on how to make asphaltene precipitation studies within the Oil Source will be presented in future VMG Newsletter.


A couple of changes have been implemented in this tab in order to show the relevant settings to be used based on the selected application type.

Load Parameters for

This box defines different sets of Regressed Parameters and Settings depending on the selected fluid type. The Oil Source will provide the best guesses for the parameters of each fluid type to make the regression process faster. Options are: Naphtha, Light Gas Oil, Middle Distillate, Heavy gas Oil, Atmospheric Residue and Vacuum Residue.

Regressed Parameters

The frame shows the resulting values of different regressed parameters for the adjustment of the composition of the slate to match experimental data. Depending on the Application type, different regressed parameters will be available:

Tight Fluids:


Oil / Refinery:




Gamma Distribution Parameters

Parameters Alpha, Beta, Scale and Shift are parameters used in the Gamma distribution probability density function that calculates the stale’s composition.


These values are different distribution scale factors for the compositions of different chemical families (P, I, O, N, A, Adh) predicted by the gamma distribution probability density function.

Delta IBP and EBP

These are adjustment factors for the initial and end boiling points of the hydrocarbon slate when a distillation curve is provided.

SARA Splits

Distribution scale factors for the composition of the SARA families based on in-house developed correlations that relate pairs of families (Saturate / Aromatic, Aromatic / Resin, Resin / Asphaltene). Only available when the Application type is Oil / Refinery.

Resin and Asphaltene Distribution Parameters

These parameters are only available when the Application type is Deasphalting. The parameters refer to Gamma distribution variables that control the amount of the Resins and Asphaltenes to be precipitated by a given solvent, by default only the Asphaltene parameters participate in the automatic regression (Regress Parameters button), if a user wants to include the Resins parameters, they would have to be included in a custom regression case (Custom Regression Case... button).

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