Handling of fluid compositions and PVT data is a key element in PVTsim. Compositional analyses from a standard PVT report are easily entered into and stored in PVTsim. When opening the compositional input menu, a default list of components is shown. Additional components may be retrieved from PVTsim's comprehensive component database, or the default list of components may be changed to comply with the user's individual needs.
Important features included with the Fluid Preprocessor module include:
- Fluid property database
- Input of plus, no-plus, or characterized fluid compositions
- Flexible lumping options and preset lumping schemes
- Recombination of separator oil & gas
- Mix up to 50 different fluids
- Weave up to 50 different fluids while maintaining original fluid components
- Convert ions from a standard water analysis to salt composition in mol%
PVTsim provides 3 different compositional input options. One is the classical molar or weight based fluid compositional input with molecular weights and densities input for each C7+ fraction. In this mode, molecular weights and densities are needed for each C7+ carbon number fraction. The user may rely on default values, or enter molecular weights and densities from a PVT report. Another input mode is for extended GC fluid analyses, which allows the user to input compositional data in the format reported by PVT labs. The third compositional input type is for a True Boiling Point (TBP) Analysis for a stable oil which converts the lab reported data into a molar composition that can be used in simulations, possibly after recombination with a gas composition to create the full reservoir fluid composition.
By default PVTsim handles components up to C80, but components up to C200 can be handled by use of an optional heavy oil characterization procedure.
By characterizing a plus fraction type of fluid, all component properties needed in subsequent simulations are established. The plus fraction is extrapolated to max. C200 and the C7+ components are grouped into pseudo-components. Characterization can be set to match saturation point.
User defined lumping is an option. A defined component may be grouped with any other defined component. The C7+ carbon number fractions may be lumped into a user specified number of components, and the user may as an option specify carbon number cut points. Lumped compositions may be delumped to full component number again.
Previously characterized fluids may also be entered. A "Complete" button enables missing properties to be estimated.
The Property Generator makes it possible to generate custom fluid property tables as a function of pressure and temperature or generate property input for a program which does not have a dedicated interface available in PVTsim.
PVTsim may be used with the SRK or the PR equation of state (76 or 78 modifications) with or without volume translation. Temperature dependent volume translation parameters are an option. The PC-SAFT and GERG-2008 are non-cubic EoS models available in PVTsim. An additional polar model can be selected from a separate drop-down menu. For example, with the SRK EoS, polar components can be modeled using Huron-Vidal, CPA, or Classical mixing rule. Separating the model with polar components from the non-polar allows the user to first tune the fluid using the standard cubic EoS, followed by application of the desired polar component model.
Bottom hole samples are often contaminated by base oil from drilling mud. Numerical decontamination of reservoir fluid compositions may be accomplished by use of the "OBM Cleaning" option. The OBM Cleaning feature can estimate the OBM contaminate composition and wt% contamination when it is not available. Contaminated measured PVT data can be input, simulated, and used for regression. The result is a cleaned reservoir fluid composition that can be saved and used for reservoir related simulation studies.