PVT Laboratories can often supply additional information on the fluid
composition in terms of a SARA analysis. This defines the relative amounts of components that are saturates, aromatics, resins and asphaltenes. The amo unts of saturates and aromatics are used in some characterisation schemes. Our current characterisation does not use this information but future extensions may do so.
The SARA analysis is used by our asphaltene model. Currently, if you enter amounts for resin or asphaltene these components will be added to your mixture and will therefore affect your phase equilibria calculations. However, without an asphaltene model you should not infer that you can calculate asphaltene
deposition.
In general the SARA Analysis should only be used with the asphaltene model. If the amount of asphaltene or the resin/asphaltene ratio is unknown, it can be estimated by the characterisation procedure by ticking the Estimate RA text box.
However, we recommend that you should use the experimental data if you know them.
Characterisation
The characterisation procedure can be used to split or regroup the heavy end from C6 to the heaviest SCN and to allocate physical properties to the resulting pseudo components. There are two characterisation procedures, Infonanal1 (the original method) and Infoanal2 (the revised method which also allows a n-paraffin distribution). If your problem has been stored in an .mfl file then the choice of characterisation procedure will also have been stored. Otherwise the first choice in the characterisation procedure is to choose the characterisation method; by default this will be set to Infoanal2.
Perhaps the simplest case is to use the characterisation to allocate physical properties to the SCNs already defined by the PVT Analysis. To do this, in the Pseudo components section
Scroll “Start pseudo components at” until you reach the heaviest SCN in your mixture
Scroll “Number of pseudo components required” to 1 Click on “Do Characterisation”
You should see a message to indicate that the characterisation has been successfully completed
If you are using Infoanal1 then the pseudo components and their compositions will be reflected in the main window on closing the PVT analysis form . In this case the amounts should match those entered. This will also be true for
Infoanal2 but in this case there is an intermediate step which plots a comparison of the experimental analysis and the fitted distribution.
If you do not wish to see this plot then it can be disabled by unchecking the
“Display SCN distribution” check box in the bottom left-hand corner of the PVT Lab Analysis form.
The physical properties related to any pseudo component may be viewed as usual using the Tools/Pure Component Data option.
Splitting and regrouping the heavy end is very flexible. For example, to split the heaviest SCN into five further fractions simply
Scroll “Start pseudo components at” until you reach the heaviest SCN in your mixture
Scroll “Number of pseudo components required” to 5 Click on “Do Characterisation”
Or to reduce the total number of SCNs from 10 (C6 to C15 for example) to 5 Scroll “Start pseudo components at” until you reach a suitable start ing point e.g.
C6
Scroll “Number of pseudo components required” to 5 Click on “Do Characterisation”
You can start the pseudo component split anywhere from C6 to the heaviest SCN in your mixture. If you try to go beyond the heaviest SCN, you will be warned that you are exceeding this value
Similarly, you can split the heavy end into any positive number of pseudo components within the overall Multiflash limit of a maximum of 200 components in a mixture. If you try to go beyond this you will see errors reported, such as
If you ask for a large number of pseudo components, but less than the overall maximum, the characterisation will reproduce this as closely as possible but restrictions on the overall mass of the C6+ fraction may mean that the total number of pseudo components cannot be achieved.
The names allocated to the pseudo component fractions will be generated by Multiflash and be of the form C11-15. If you choose to use the revised Infoanal2 characterisation without defining or estimating a n-paraffin distribution the output will be similar.
If you wish to have a separate n -paraffin distribution you either enter the experimental compositions using the appropriate form or supply a wax content by either entering a known value or asking Multiflash to estimate this. You can then characterise the n -paraffin distribution in the same way as you do for the remaining fluid. In this case n-paraffin fractions are designated by the letter N, e.g. N11-15, and fractions in the remainder of the fluid by the letter I. If the n-paraffin distribution is estimated a warning message to this effect will be displayed
The n-paraffin distribution need not be identical to the remaining fluid
distribution. For use with the Coutinho wax model our suggested default is C6 and 5 fractions for the main fluid and N6 and 15 fractions for the n-paraffin distribution.
If an experimental n-paraffin distribution is supplied using the option then the experimental and fitted data for this distribution will be shown.