neqsim-wax-calculations

NeqSim Wax Calculations

Use this skill when a task needs a real NeqSim wax workflow rather than the simple wax-margin screening placeholder. Typical outputs are wax appearance temperature (WAT), wax weight fraction versus temperature, wax fraction along a pressure profile, waxy-oil viscosity sensitivity, and optional inhibitor dose-response screening.

When to Use

• A user asks for wax appearance temperature, WAT, wax precipitation, or wax phase calculations.
• A flow-assurance study needs wax fraction as a function of temperature or pressure.
• A crude assay contains TBP or plus fractions that can be characterized into wax-forming pseudo-components.
• A wax inhibitor, pour-point depressant, or cold-restart discussion needs a NeqSim WAT basis.
• A task needs to compare an operating or pipeline temperature profile against wax onset.

For a quick margin calculation when WAT is already known, use neqsim-wax-margin-check. For broader pipeline and hydrate/wax/asphaltene context, also load neqsim-flow-assurance.

Required Inputs

• Oil or condensate composition including wax-forming heavy fractions. Prefer measured TBP cuts and plus-fraction molar mass and density.
• Pressure in bara for the WAT or wax fraction calculation.
• Temperature range in Celsius for wax fraction curves.
• Wax model choice when specified: Pedersen default, Won, Wilson, or Coutinho via setWaxModelType(String) before adding the wax phase.
• Optional lab data: measured WAT, DSC wax fraction, pour point, yield stress, inhibitor dose-response, or viscosity versus shear rate.

Wax Fluid Setup

Wax calculations need a characterized heavy-end oil and an explicit wax solid phase. The verified Java setup pattern is:

SystemInterface oil = new SystemSrkEos(273.15 + 60.0, 50.0);
oil.addComponent("methane", 0.30);
oil.addComponent("ethane", 0.10);
oil.addTBPfraction("C10", 0.15, 134.0 / 1000.0, 0.78);
oil.addTBPfraction("C15", 0.15, 206.0 / 1000.0, 0.83);
oil.addTBPfraction("C19", 0.10, 270.0 / 1000.0, 0.814);
oil.addPlusFraction("C20", 0.20, 350.0 / 1000.0, 0.88);

oil.getCharacterization().characterisePlusFraction();
oil.getWaxModel().addTBPWax();
oil.createDatabase(true);
oil.setMixingRule(2);
oil.addSolidComplexPhase("wax");
oil.setMultiphaseWaxCheck(true);
oil.setMultiPhaseCheck(true);
oil.init(0);
oil.init(1);

Notes:

• Use plus-fraction names without +, for example "C20", not "C20+".
• Call characterisePlusFraction() before getWaxModel().addTBPWax().
• Call setWaxModelType("Won"), setWaxModelType("Wilson"), or setWaxModelType("Coutinho") before addSolidComplexPhase("wax") if the default Pedersen model is not intended.
• Keep the heavy-end basis traceable. Wax predictions are very sensitive to molar mass, density, and n-paraffin distribution.

Wax Appearance Temperature

Use ThermodynamicOperations#calcWAT() for a direct WAT. The operation changes the system temperature to the calculated wax appearance temperature.

ThermodynamicOperations ops = new ThermodynamicOperations(oil);
ops.calcWAT();
double watC = oil.getTemperature() - 273.15;

Use this for a single pressure point when the fluid has already been configured for wax calculations.

Wax Fraction Curve

Use neqsim.pvtsimulation.flowassurance.WaxCurveCalculator for a WAT and wax weight fraction curve with monotonicity enforcement.

WaxCurveCalculator wax = new WaxCurveCalculator(oil);
wax.setPressure(50.0);
wax.setTemperatureRange(-10.0, 80.0, 2.0);
wax.calculate();

double watC = wax.getWaxAppearanceTemperatureC();
double[] temperaturesC = wax.getTemperaturesC();
double[] waxWeightFractions = wax.getWaxWeightFractions();
int failedFlashes = wax.getFailCount();
int corrections = wax.getMonotonicityCorrections();

Temperature values are stored from high to low temperature. Wax fraction should increase as temperature decreases. Record failedFlashes and corrections in the task results so reviewers can judge numerical quality.

Pipeline Pressure Sensitivity

Use calculateAtMultiplePressures(double[], double) to evaluate wax fraction at one temperature across a pipeline pressure profile.

double[] pressuresBara = new double[] {120.0, 90.0, 60.0, 30.0};
Map<Double, Double> waxByPressure = wax.calculateAtMultiplePressures(pressuresBara, 25.0);

For a full pipeline profile, combine this with the pipeline temperature profile from a NeqSim pipe model or measured operating data. Compare local temperature against WAT at local pressure, and report wax fraction at each profile point.

PVT Wax Fraction Simulation

Use WaxFractionSim when the task follows the PVT simulation pattern or needs compatibility with existing PVT reports.

WaxFractionSim waxSim = new WaxFractionSim(oil);
double[] temperaturesK = new double[] {333.15, 313.15, 293.15, 273.15};
double[] pressuresBara = new double[] {50.0, 50.0, 50.0, 50.0};
waxSim.setTemperaturesAndPressures(temperaturesK, pressuresBara);
waxSim.runCalc();
double[] waxFractions = waxSim.getWaxFraction();

The array returned by getWaxFraction() is the system weight fraction in the wax phase at each pressure and temperature point.

Waxy-Oil Viscosity

Use ViscosityWaxOilSim when viscosity increase below WAT or shear-rate sensitivity matters. Configure the wax fluid as above, then set matching temperature, pressure, and shear-rate arrays. Treat results as model-sensitive and validate against lab viscosity data when available.

Wax Inhibitor Screening

For inhibitor or pour-point-depressant screening, first calculate the untreated WAT using WaxCurveCalculator or calcWAT(). Then use neqsim.process.chemistry.wax.WaxInhibitorPerformance for a transparent dose-response estimate.

WaxInhibitorPerformance inhibitor = new WaxInhibitorPerformance();
inhibitor.setBaseWaxAppearanceTemperatureC(watC);
inhibitor.setBasePourPointC(24.0);
inhibitor.setDoseMgL(200.0);
inhibitor.setMaxPourPointDepressionC(18.0);
inhibitor.setDoseAt50PctEfficacyMgL(150.0);
inhibitor.evaluate();

double inhibitedWatC = inhibitor.getInhibitedWaxAppearanceTemperatureC();
double efficacy = inhibitor.getEfficacyFraction();
List<String> warnings = inhibitor.getWarnings();

This inhibitor model is a screening relation. Use lab bottle tests, cold-finger data, and field-trial evidence for design decisions.

Python Notebook Pattern

In repository task notebooks, use devtools/neqsim_dev_setup.py and direct Java classes through ns so the workspace classes are used.

SystemSrkEos = ns.SystemSrkEos
ThermodynamicOperations = ns.ThermodynamicOperations
WaxCurveCalculator = ns.JClass("neqsim.pvtsimulation.flowassurance.WaxCurveCalculator")

oil = SystemSrkEos(273.15 + 60.0, 50.0)
oil.addComponent("methane", 0.30)
oil.addComponent("ethane", 0.10)
oil.addTBPfraction("C10", 0.15, 134.0 / 1000.0, 0.78)
oil.addTBPfraction("C15", 0.15, 206.0 / 1000.0, 0.83)
oil.addPlusFraction("C20", 0.20, 350.0 / 1000.0, 0.88)

oil.getCharacterization().characterisePlusFraction()
oil.getWaxModel().addTBPWax()
oil.createDatabase(True)
oil.setMixingRule(2)
oil.addSolidComplexPhase("wax")
oil.setMultiphaseWaxCheck(True)
oil.setMultiPhaseCheck(True)
oil.init(0)
oil.init(1)

wax = WaxCurveCalculator(oil)
wax.setPressure(50.0)
wax.setTemperatureRange(-10.0, 80.0, 2.0)
wax.calculate()

wat_c = wax.getWaxAppearanceTemperatureC()
temperatures_c = list(wax.getTemperaturesC())
wax_weight_fractions = list(wax.getWaxWeightFractions())

Validation Checklist

• Heavy-end composition has measured or documented TBP and plus-fraction molar mass and density.
• Plus fraction was characterized before wax pseudo-components were added.
• A wax solid phase was added and setMultiphaseWaxCheck(true) was enabled.
• WAT was compared against at least one independent reference when possible: lab WAT, DSC data, pour point trend, or published example.
• Wax fraction curve has physically monotonic behavior after any documented corrections.
• Failed flash count and monotonicity corrections are recorded.
• Sensitivity to pressure, heavy-end characterization, and wax model type is discussed for design-grade work.
• Results are not used for pigging intervals, deposition growth, or restart design without deposition and rheology validation.

Common Failure Modes

Reporting Requirements

For task reports, include:

• EOS and wax model type.
• Full heavy-end basis and units.
• WAT in Celsius at each pressure.
• Wax fraction curve table or figure with temperature in Celsius and wax weight fraction.
• Numerical quality indicators: failed flashes, monotonicity corrections, and sensitivity checks.
• Assumptions, validation source, and limits of use.

Related NeqSim Classes

• neqsim.thermodynamicoperations.ThermodynamicOperations#calcWAT()
• neqsim.pvtsimulation.flowassurance.WaxCurveCalculator
• neqsim.pvtsimulation.simulation.WaxFractionSim
• neqsim.pvtsimulation.simulation.ViscosityWaxOilSim
• neqsim.process.chemistry.wax.WaxInhibitorPerformance
• neqsim.thermo.characterization.WaxModelInterface
• neqsim.thermo.phase.PhaseWax

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