PVT Simulation Workflows

This guide covers PVT simulation workflows in NeqSim, backed by regression tests under src/test/java/neqsim/pvtsimulation/simulation. Use these tested setups to reproduce experiments in your own studies.

Constant Volume Depletion (CVD)

CVD simulation maintains reservoir volume constant while reducing pressure, measuring the liquid dropout from gas condensate reservoirs.

Basic CVD Setup

import neqsim.pvtsimulation.simulation.ConstantVolumeDepletion;
import neqsim.thermo.system.SystemSrkEos;

// Create fluid with TBP fractions
SystemSrkEos fluid = new SystemSrkEos(97.5 + 273.15, 300.0);  // T(K), P(bara)
fluid.addComponent("nitrogen", 0.34);
fluid.addComponent("CO2", 3.59);
fluid.addComponent("methane", 67.42);
fluid.addComponent("ethane", 9.02);
fluid.addComponent("propane", 4.31);
fluid.addComponent("i-butane", 0.93);
fluid.addComponent("n-butane", 1.71);
fluid.addComponent("i-pentane", 0.74);
fluid.addComponent("n-pentane", 0.85);
fluid.addTBPfraction("C6", 1.38, 86.0 / 1000, 0.664);
fluid.addTBPfraction("C7", 1.57, 96.0 / 1000, 0.738);
fluid.addTBPfraction("C8", 1.73, 107.0 / 1000, 0.765);
fluid.addTBPfraction("C9", 1.40, 121.0 / 1000, 0.781);
fluid.addTBPfraction("C10+", 5.01, 230.0 / 1000, 0.820);

fluid.setMixingRule("classic");
fluid.useVolumeCorrection(true);
fluid.init(0);
fluid.init(1);

// Configure CVD simulation
ConstantVolumeDepletion cvd = new ConstantVolumeDepletion(fluid);
cvd.setTemperature(97.5, "C");
cvd.setPressures(new double[] {300, 250, 200, 150, 100, 50});  // bara

// Run simulation
cvd.runCalc();

// Get results
double[] relativeVolume = cvd.getRelativeVolume();
double[] liquidVolumeFraction = cvd.getLiquidVolume();
double[] Zgas = cvd.getZgas();

CVD Setup Checklist

  1. Create SystemInterface with EOS and add components/TBP fractions
  2. Enable database use and select a mixing rule
  3. Initialize the system (state 0 and 1) before constructing ConstantVolumeDepletion
  4. Call setTemperature(...), setPressures(...), and runCalc()
  5. Optionally load experimental data for regression with setExperimentalData(...)
  6. Retrieve results: getRelativeVolume(), getLiquidVolume(), getZgas()

Differential Liberation (DL)

DL simulation removes liberated gas at each pressure step, measuring oil shrinkage and gas evolution - essential for black oil PVT tables.

Basic DL Setup

import neqsim.pvtsimulation.simulation.DifferentialLiberation;
import neqsim.thermo.system.SystemSrkEos;

// Create rich oil system with TBP characterization
SystemSrkEos fluid = new SystemSrkEos(97.5 + 273.15, 250.0);
fluid.addComponent("nitrogen", 0.5);
fluid.addComponent("CO2", 2.1);
fluid.addComponent("methane", 45.0);
fluid.addComponent("ethane", 7.5);
fluid.addComponent("propane", 5.2);
fluid.addComponent("i-butane", 1.1);
fluid.addComponent("n-butane", 2.8);
fluid.addComponent("i-pentane", 1.4);
fluid.addComponent("n-pentane", 1.9);
fluid.addTBPfraction("C6", 2.5, 86.0 / 1000, 0.685);
fluid.addTBPfraction("C7", 4.2, 96.0 / 1000, 0.755);
fluid.addTBPfraction("C8", 3.8, 107.0 / 1000, 0.775);
fluid.addTBPfraction("C9", 3.2, 121.0 / 1000, 0.790);
fluid.addTBPfraction("C10+", 18.8, 350.0 / 1000, 0.880);

fluid.setMixingRule("classic");
fluid.useVolumeCorrection(true);
fluid.init(0);
fluid.init(1);

// Configure DL simulation
DifferentialLiberation dl = new DifferentialLiberation(fluid);
dl.setTemperature(97.5, "C");
dl.setPressures(new double[] {250, 225, 200, 175, 150, 125, 100, 75, 50, 25, 1});

// Run simulation
dl.runCalc();

// Get results
double[] Bo = dl.getBo();           // Oil formation volume factor
double[] Rs = dl.getRs();           // Solution gas-oil ratio (Sm3/Sm3)
double[] Bg = dl.getBg();           // Gas formation volume factor
double[] oilDensity = dl.getOilDensity();

Interpreting DL Outputs

Property Description Expected Trend
Bo Oil formation volume factor (Vres/Vstock) Decreases from ~1.7 to ~1.05 as pressure drops
Rs Solution gas-oil ratio Decreases to zero at final stage
Bg Gas formation volume factor Increases as gas expands at lower pressure
Oil Density Density of remaining oil Increases as light components liberate

Constant Composition Expansion (CCE)

CCE measures PV behavior without removing any material - used to determine bubble/dew point pressure.

import neqsim.pvtsimulation.simulation.ConstantMassExpansion;

// After creating and initializing fluid...
ConstantMassExpansion cce = new ConstantMassExpansion(fluid);
cce.setTemperature(100.0, "C");

// Run to find saturation pressure
cce.runCalc();

double saturationPressure = cce.getSaturationPressure();
double[] relativeVolume = cce.getRelativeVolume();
double[] Ytfactor = cce.getYfactor();

Saturation Pressure Calculation

Quick calculation of bubble or dew point pressure:

import neqsim.thermodynamicoperations.ThermodynamicOperations;

ThermodynamicOperations ops = new ThermodynamicOperations(fluid);

// For bubble point (oil system)
ops.calcBubblePoint();
double bubbleP = fluid.getPressure("bara");

// For dew point (gas condensate)
ops.calcDewPoint();
double dewP = fluid.getPressure("bara");

Slim Tube Simulation

Minimum miscibility pressure (MMP) determination:

import neqsim.pvtsimulation.simulation.SlimTubeSim;

// Create injection gas
SystemSrkEos injectionGas = new SystemSrkEos(373.15, 200.0);
injectionGas.addComponent("CO2", 1.0);
injectionGas.setMixingRule("classic");

// Configure slim tube
SlimTubeSim slimTube = new SlimTubeSim(reservoirFluid, injectionGas);
slimTube.setTemperature(100.0, "C");
slimTube.setPressures(new double[] {150, 200, 250, 300, 350, 400});
slimTube.runCalc();

double[] recovery = slimTube.getOilRecovery();

Best Practices

  1. Always initialize - Set mixing rule and call init(0) and init(1) before creating PVT simulations
  2. Set temperature explicitly - Use setTemperature() on each simulation to avoid state carryover
  3. Use volume correction - Enable useVolumeCorrection(true) for better liquid density predictions
  4. Validate against lab data - Use setExperimentalData() methods for regression
  5. Check convergence - Verify flash calculations converge at each pressure step