PVT and Fluid Characterization

Accurate phase behavior predictions start with a realistic fluid description. NeqSim supports full compositional models, TBP cuts, and black-oil style pseudo-components.

Building Compositions

  1. Known components: Add pure components directly using critical-property data from the internal database.
  2. Plus fractions (C7+): Use addPlusFraction(name, moles, molarMass, density) when only overall heavy fraction data are available.
  3. TBP/assay data: Use addTBPfraction(name, moles, density, molarMass) to preserve multiple heavy cuts with their own boiling ranges.
SystemInterface oil = new SystemSrkEos(323.15, 150.0);
oil.createDatabase(true);
oil.addComponent("nitrogen", 0.01);
oil.addComponent("methane", 0.60);
oil.addTBPfraction("C7", 0.08, 0.73, 7.5);
oil.addTBPfraction("C10", 0.10, 0.80, 10.5);
oil.addPlusFraction("C20+", 0.21, 0.92, 22.0);
oil.setMixingRule(2);

Tuning and Regression

Lumping Models

After plus-fraction splitting generates many single-carbon-number (SCN) components, lumping groups them for computational efficiency.

// PVTlumpingModel: Preserve C6-C9 TBP fractions, lump only C10+ into 6 groups
oil.getCharacterization().configureLumping()
    .model("PVTlumpingModel")
    .plusFractionGroups(6)
    .build();

// Standard model: Lump all heavy fractions (C6-C80) into 5 pseudo-components
oil.getCharacterization().configureLumping()
    .model("standard")
    .totalPseudoComponents(5)
    .build();

// Custom boundaries: Match PVT lab report groupings (C6, C7-C9, C10-C19, C20+)
oil.getCharacterization().configureLumping()
    .customBoundaries(6, 7, 10, 20)
    .build();

// No lumping: Keep all individual SCN components (for detailed studies)
oil.getCharacterization().configureLumping()
    .noLumping()
    .build();

Lumping Model Comparison

Model Behavior Use Case
PVTlumpingModel Preserves C6-C9 as individual pseudo-components, lumps only C10+ Standard PVT matching
standard Lumps all heavy fractions from C6 onwards Minimal components for fast simulation
no lumping Keeps all individual SCN components Detailed compositional studies

For more details on the mathematical background, see Fluid Characterization Mathematics.

Asphaltene Modeling

For fluids with asphaltene precipitation risk, use the PedersenAsphalteneCharacterization class:

import neqsim.thermo.characterization.PedersenAsphalteneCharacterization;

// Create asphaltene characterization
PedersenAsphalteneCharacterization asphChar = new PedersenAsphalteneCharacterization();
asphChar.setAsphalteneMW(750.0);     // Molecular weight g/mol
asphChar.setAsphalteneDensity(1.10); // Density g/cm³

// Add asphaltene as pseudo-component (before mixing rule)
asphChar.addAsphalteneToSystem(oil, 0.02);  // 2 mol% asphaltene
oil.setMixingRule("classic");

// Perform TPflash with asphaltene detection
boolean hasAsphaltene = PedersenAsphalteneCharacterization.TPflash(oil);

NeqSim supports two asphaltene phase types:

PVT Reports

After running ThermodynamicOperations.TPflash(), collect standard PVT outputs:

oil.initProperties();
System.out.println("Bo at separator: " + oil.getPhase("oil").getVolume() / oil.getTotalNumberOfMoles());
System.out.println("GOR at separator: " + oil.getPhase("gas").getNumberOfMoles()/oil.getPhase("oil").getNumberOfMoles());

For multi-stage separators, clone the fluid after each flash and continue flashing at downstream conditions.

Data Management