Asphaltene Method Comparison

Overview

NeqSim provides two complementary approaches for asphaltene stability analysis:

De Boer Screening: Fast, empirical correlation for initial assessment
CPA Thermodynamic Modeling: Rigorous EOS-based onset calculations

This document explains when to use each method and how to compare their results.

Method Summary

Aspect	De Boer	CPA
Speed	Milliseconds	Seconds to minutes
Input Required	P_res, P_bub, ρ	Full composition + properties
Output	Risk category	Onset P, T, amounts
Accuracy	Conservative screening	Predictive (if tuned)
Composition Effects	No	Yes
Temperature Effects	No	Yes
Injection Effects	No	Yes

Decision Framework

When to Use De Boer Only

✅ Early field screening with limited data
✅ Quick portfolio risk ranking
✅ Conservative go/no-go decisions
✅ Baseline risk communication

When to Use CPA Only

✅ Detailed well/facility design
✅ Operating envelope definition
✅ Gas injection impact assessment
✅ Inhibitor effectiveness evaluation

When to Use Both

✅ Field development planning (screen then analyze)
✅ Validating thermodynamic model predictions
✅ Communicating risk to non-technical stakeholders
✅ Comprehensive flow assurance studies

Using AsphalteneMethodComparison

Basic Comparison

import neqsim.pvtsimulation.flowassurance.AsphalteneMethodComparison;
import neqsim.thermo.system.SystemSrkCPAstatoil;

// Create CPA fluid
SystemSrkCPAstatoil fluid = new SystemSrkCPAstatoil(373.15, 350.0);
fluid.addComponent("methane", 0.40);
fluid.addComponent("n-heptane", 0.50);
fluid.addComponent("asphaltene", 0.10);
fluid.setMixingRule("classic");
fluid.init(0);
fluid.init(1);

// Create comparison
AsphalteneMethodComparison comparison = new AsphalteneMethodComparison(fluid);
comparison.setReservoirPressure(350.0);
comparison.setBubblePointPressure(150.0);
comparison.setInSituDensity(720.0);

// Run comparison
String report = comparison.runComparison();
System.out.println(report);

Sample Output

=================================================
ASPHALTENE STABILITY: METHOD COMPARISON REPORT
=================================================

FLUID INFORMATION
-----------------
Temperature: 100.0 °C
Pressure: 350.0 bar
Number of Components: 3

DE BOER SCREENING RESULTS
-------------------------
Undersaturation: 200.0 bar
In-situ Density: 720.0 kg/m³
Risk Level: MODERATE_PROBLEM
Risk Index: 0.55

CPA THERMODYNAMIC RESULTS
-------------------------
Asphaltene Onset Pressure: 185.0 bar
Above Bubble Point: Yes
Precipitation Expected: Yes
Onset Margin: 35.0 bar above bubble point

COMPARISON SUMMARY
------------------
De Boer Risk: MODERATE
CPA Prediction: Precipitation at 185 bar

Agreement: CONSISTENT
Both methods indicate asphaltene precipitation 
risk during normal production.

RECOMMENDATIONS
---------------
1. Consider asphaltene inhibitor injection
2. Design for periodic wellbore cleanout
3. Monitor production for pressure decline
4. Validate with laboratory AOP test

Quick Summary

For rapid assessment:

String summary = comparison.getQuickSummary();
System.out.println(summary);

Output:

De Boer: MODERATE_PROBLEM | CPA Onset: 185 bar | Agreement: CONSISTENT

Interpretation Guidelines

Consistent Results

De Boer	CPA	Interpretation
NO_PROBLEM	No onset found	Low risk, minimal mitigation
SLIGHT_PROBLEM	Onset near P_bub	Monitor during late life
MODERATE_PROBLEM	Onset > P_bub	Active mitigation needed
SEVERE_PROBLEM	Onset » P_bub	Significant risk, design for it

Inconsistent Results

De Boer	CPA	Possible Causes
HIGH	No onset	De Boer conservative; unusual composition
LOW	Onset found	Light oil with high asphaltene; check composition

When results disagree:

Review input data quality
Check CPA model tuning
Consider laboratory validation
Use more conservative result for design

Example Workflows

Workflow 1: Field Development Screening

// Step 1: De Boer screening of all fluids
List<String> needsDetailedAnalysis = new ArrayList<>();

for (FluidSample sample : allSamples) {
    DeBoerAsphalteneScreening screening = new DeBoerAsphalteneScreening(
        sample.getReservoirPressure(),
        sample.getBubblePoint(),
        sample.getInSituDensity()
    );
    
    String risk = screening.evaluateRisk();
    
    if (!risk.equals("NO_PROBLEM")) {
        needsDetailedAnalysis.add(sample.getName());
    }
}

// Step 2: CPA analysis only for flagged samples
for (String sampleName : needsDetailedAnalysis) {
    // Create detailed CPA model
    SystemSrkCPAstatoil fluid = createCPAFluid(sampleName);
    
    AsphalteneStabilityAnalyzer analyzer = 
        new AsphalteneStabilityAnalyzer(fluid);
    
    double onsetP = analyzer.calculateOnsetPressure();
    
    System.out.printf("Sample %s: Onset at %.1f bar%n", 
                      sampleName, onsetP);
}

Workflow 2: Operating Envelope Definition

// Use CPA to define safe operating window
AsphalteneStabilityAnalyzer analyzer = new AsphalteneStabilityAnalyzer(fluid);

// Generate precipitation boundary
double[][] envelope = analyzer.generatePrecipitationEnvelope(
    280.0, 420.0, 10.0  // Temperature range [K]
);

// Define operating envelope with safety margin
double safetyMargin = 20.0;  // bar below onset

System.out.println("Safe Operating Envelope:");
System.out.println("T [°C], Max P [bar]");
for (int i = 0; i < envelope[0].length; i++) {
    double T_C = envelope[0][i] - 273.15;
    double maxSafeP = envelope[1][i] - safetyMargin;
    System.out.printf("%.0f, %.1f%n", T_C, maxSafeP);
}

Workflow 3: Blending Compatibility

// Base fluid
SystemSrkCPAstatoil baseFluid = createFluid("FieldA");

// Blend fluid  
SystemSrkCPAstatoil blendFluid = createFluid("FieldB");

// Test blend ratios
double[] blendRatios = {0.0, 0.25, 0.50, 0.75, 1.0};

System.out.println("Blend Compatibility Study");
System.out.println("-------------------------");

for (double ratio : blendRatios) {
    SystemSrkCPAstatoil mixed = blendFluids(baseFluid, blendFluid, ratio);
    
    AsphalteneStabilityAnalyzer analyzer = 
        new AsphalteneStabilityAnalyzer(mixed);
    
    double onsetP = analyzer.calculateOnsetPressure();
    String deBoer = analyzer.deBoerScreening();
    
    System.out.printf("%.0f%% Field B: Onset = %.1f bar, De Boer = %s%n",
                      ratio * 100, onsetP, deBoer);
}

Model Validation

Laboratory Data Requirements

For CPA model tuning:

Test	Purpose	Priority
AOP Test	Onset pressure at reservoir T	Required
HPM Analysis	Onset detection and quantification	Recommended
SARA Analysis	Composition for characterization	Required
Titration	Onset with n-heptane at ambient	Optional
Density	For De Boer screening	Required

Automated Parameter Tuning

NeqSim provides the AsphalteneOnsetFitting class for automated CPA parameter tuning:

import neqsim.pvtsimulation.util.parameterfitting.AsphalteneOnsetFitting;

// Create fitter with your fluid system
AsphalteneOnsetFitting fitter = new AsphalteneOnsetFitting(fluid);

// Add experimental AOP data from lab tests
fitter.addOnsetPointCelsius(80.0, 350.0);   // 80°C, 350 bar
fitter.addOnsetPointCelsius(100.0, 320.0);  // 100°C, 320 bar
fitter.addOnsetPointCelsius(120.0, 280.0);  // 120°C, 280 bar

// Set initial parameter guesses based on oil type
// Light oils: epsilon/R=3000, kappa=0.01
// Heavy oils: epsilon/R=4000, kappa=0.003
fitter.setInitialGuess(3500.0, 0.005);

// Run Levenberg-Marquardt optimization
boolean success = fitter.solve();

if (success) {
    // Get fitted parameters
    double epsilonR = fitter.getFittedAssociationEnergy();
    double kappa = fitter.getFittedAssociationVolume();
    
    System.out.printf("Fitted ε/R: %.1f K%n", epsilonR);
    System.out.printf("Fitted κ: %.4f%n", kappa);
    
    // Predict onset at new temperature
    double predictedAOP = fitter.calculateOnsetPressure(393.15);  // 120°C
    System.out.printf("Predicted AOP at 120°C: %.1f bar%n", predictedAOP);
}

Manual Tuning Process

For manual iteration without the automated fitter:

// Experimental AOP
double measuredAOP = 195.0;  // bar at 100°C

// Initial CPA prediction
AsphalteneStabilityAnalyzer analyzer = 
    new AsphalteneStabilityAnalyzer(fluid);
double predictedAOP = analyzer.calculateOnsetPressure();

// Calculate error
double error = predictedAOP - measuredAOP;
System.out.printf("Initial error: %.1f bar%n", error);

// Adjust asphaltene parameters to match
// Options: molecular weight, critical properties, kij values
// Iterate until error < tolerance

Performance Comparison

Calculation Times (Typical)

Operation	Time	Notes
De Boer screening	< 1 ms	Single correlation evaluation
De Boer batch (1000 samples)	< 100 ms	Highly parallelizable
CPA single flash	10-100 ms	Depends on composition
CPA onset pressure	1-5 s	Multiple flashes + bisection
CPA full envelope	10-60 s	Many onset calculations
Parameter fitting (3 points)	10-60 s	Depends on convergence
Full comparison report	2-10 s	Both methods + formatting

When Speed Matters

// For real-time monitoring: Use De Boer only
if (isRealTimeMonitoring) {
    DeBoerAsphalteneScreening screening = 
        new DeBoerAsphalteneScreening(pRes, pBub, density);
    return screening.calculateRiskIndex();
}

// For batch screening: Use De Boer first
if (numberOfSamples > 100) {
    // Screen with De Boer
    List<Sample> flagged = deBoerScreen(samples);
    
    // CPA only on flagged samples
    for (Sample s : flagged) {
        runCPAAnalysis(s);
    }
}

Best Practices

Do’s

✅ Start with De Boer for initial assessment
✅ Validate CPA with experimental data before design
✅ Use both for comprehensive studies
✅ Document assumptions in both methods
✅ Apply safety margins to predicted onset

Don’ts

❌ Don’t use CPA without tuning for critical decisions
❌ Don’t ignore De Boer warnings even if CPA looks safe
❌ Don’t over-interpret small onset pressure differences
❌ Don’t extrapolate beyond validated conditions

Example: Complete Comparison

import neqsim.pvtsimulation.flowassurance.*;
import neqsim.thermo.system.SystemSrkCPAstatoil;

public class AsphalteneStudy {
    public static void main(String[] args) {
        // Create realistic oil composition
        SystemSrkCPAstatoil fluid = new SystemSrkCPAstatoil(373.15, 350.0);
        
        // Light ends
        fluid.addComponent("nitrogen", 0.01);
        fluid.addComponent("CO2", 0.02);
        fluid.addComponent("methane", 0.35);
        fluid.addComponent("ethane", 0.08);
        fluid.addComponent("propane", 0.05);
        
        // Intermediates
        fluid.addComponent("n-butane", 0.03);
        fluid.addComponent("n-pentane", 0.03);
        fluid.addComponent("n-hexane", 0.05);
        fluid.addComponent("n-heptane", 0.15);
        fluid.addComponent("n-decane", 0.10);
        
        // Heavy ends
        fluid.addComponent("n-C15", 0.08);
        fluid.addComponent("asphaltene", 0.05);
        
        fluid.setMixingRule("classic");
        fluid.init(0);
        fluid.init(1);
        
        // Reservoir conditions
        double pRes = 350.0;    // bar
        double pBub = 150.0;    // bar
        double density = 720.0; // kg/m³
        
        // Run full comparison
        AsphalteneMethodComparison comparison = 
            new AsphalteneMethodComparison(fluid);
        comparison.setReservoirPressure(pRes);
        comparison.setBubblePointPressure(pBub);
        comparison.setInSituDensity(density);
        
        // Generate reports
        System.out.println(comparison.runComparison());
        
        System.out.println("\n" + StringUtils.repeat("=", 50));
        System.out.println("QUICK REFERENCE");
        System.out.println(StringUtils.repeat("=", 50));
        System.out.println(comparison.getQuickSummary());
    }
}

Asphaltene Method Comparison

Comprehensive Java library for thermodynamic, physical property, and process simulation. NeqSim provides tools for PVT analysis, phase equilibria, transport properties, and full process simulation.

Asphaltene Method Comparison

Overview

Method Summary

Decision Framework

When to Use De Boer Only

When to Use CPA Only

When to Use Both

Using AsphalteneMethodComparison

Basic Comparison

Sample Output

Quick Summary

Interpretation Guidelines

Consistent Results

Inconsistent Results

Example Workflows

Workflow 1: Field Development Screening

Workflow 2: Operating Envelope Definition

Workflow 3: Blending Compatibility

Model Validation

Laboratory Data Requirements

Automated Parameter Tuning

Manual Tuning Process

Performance Comparison

Calculation Times (Typical)

When Speed Matters

Best Practices

Do’s

Don’ts

Example: Complete Comparison

See Also