Tips and Tricks: Make the Most of an Extended Gas Analysis
By Chris Arthur – VMG Calgary
How to regress an extended gas analysis to a PIONA composition using the Oil Source Unit Operation
Extended gas analyses may list carbon numbers, to C30 and heavier, as fractions indicating composition and measured or calculated bulk properties. These assays are becoming prevalent in shale gas production where the C7+ fraction can be higher than in conventional gas and with significant produced liquids. The VMGSim Oil Source Unit is capable of producing a PIONA based composition from an extended analysis to best fit the bulk properties. The associated sample can then be represented in a simulation and mixed, separated and fractionated while maintaining the ability to predict fluid properties including saturation pressure, density and heating value.
To create a slate of components for the simulation enter the wholly defined compounds listed in the extended analysis as pure components. The species listed in the analysis as carbon numbers can be represented using the PIONA Slate tool of the Property Package window.
An example composition slate for a C36+ extended analysis can be seen below:
It is not necessary to include every carbon number seen in the analysis. The example slate captured the lightest carbon number component (C6) and had a finer granularity around the C6 to C11 range than the heavier range corresponding to the distribution. The heaviest component, following a rule of thumb, was selected to be 6 carbon numbers heavier than the maximum described in the sample
Using the Oil Source
To enter data from an extended analysis to the Oil Source Unit, in the Laboratory Analysis frame, select Carbon Number (Cn) Compositonal Analysis and set the type to Cn. Bulk properties from the analysis can be entered as Specified values in the Bulk Experimental Variables frame. Check the Active box to include a value in the data regression. The importance of the variable can be scaled with a lower value assigning a higher priority.
Commonly, bulk values are only associated with part of the sample, for example, density for components heavier than C7+ may be listed. Such properties can be specified in the Cn+ Fraction Properties frame. The carbon numbers associated with these bulk values should be defined in the Options frame of the Cn Analysis tab by specifying the threshold in Cn for Cn+ Fraction Properties. If a saturation pressure is listed in the analysis the saturation temperature should be defined in Saturation T in the Settings Tab.
To enter the carbon composition first select the appropriate PIONA groups in the Settings tab. The fractions for components from the extended analysis can be entered in the Cn Analysis tab. In the Options frame the carbon numbers to be included in the regression are defined under Cn Distribution Settings. The Regress Parameters button will produce a PIONA composition for the sample. A stream connected to the Oil Source will now be configured with the PIONA composition.
To represent a well head in a flowsheet the extended analysis for the liquid and gas components were used to create PIONA compositions and recombined with the produced water. In this configuration the flow rates were assigned to the streams attached to the Oil Sources and for water. Temperature and pressure data was assigned downstream of the mixer.
Bulk properties are often only attributed to part of an analysis using a carbon number threshold. In practice the components were separated by distillation and boiling point would make a better threshold. The Oil Source can be adapted by changing Cn Groups Defined by to BP Range in the Cn Analysis tab.