Flow Assurance Overview

Flow assurance ensures reliable hydrocarbon transport from reservoir to processing facility. This guide provides an integrated approach to the main flow assurance challenges using NeqSim.

Key Flow Assurance Challenges

Challenge Cause Risk NeqSim Capability
Hydrates Water + gas at low T, high P Blockage ✅ Full prediction
Wax Paraffin precipitation at low T Deposition, restart ✅ WAT calculation
Asphaltenes Pressure/composition change Deposition, fouling ✅ CPA model
Scale Mineral precipitation Blockage, corrosion ⚠️ Basic
Slugging Multiphase flow instability Equipment damage ✅ Transient models
Corrosion CO₂, H₂S, water Pipe failure ⚠️ Indirect

Quick Screening Workflow

Java - Complete Flow Assurance Screen

import neqsim.thermo.system.SystemSrkCPAstatoil;
import neqsim.thermodynamicoperations.ThermodynamicOperations;

public class FlowAssuranceScreen {
    public static void main(String[] args) {
        
        // Create production fluid
        SystemSrkCPAstatoil fluid = new SystemSrkCPAstatoil(293.15, 100.0);
        
        // Typical Gulf of Mexico fluid
        fluid.addComponent("nitrogen", 0.005);
        fluid.addComponent("CO2", 0.02);
        fluid.addComponent("H2S", 0.001);
        fluid.addComponent("methane", 0.40);
        fluid.addComponent("ethane", 0.08);
        fluid.addComponent("propane", 0.06);
        fluid.addComponent("i-butane", 0.02);
        fluid.addComponent("n-butane", 0.03);
        fluid.addComponent("i-pentane", 0.015);
        fluid.addComponent("n-pentane", 0.02);
        fluid.addComponent("n-hexane", 0.025);
        fluid.addTBPfraction("C7", 0.05, 95.0, 0.72);
        fluid.addTBPfraction("C10", 0.08, 135.0, 0.78);
        fluid.addTBPfraction("C20", 0.08, 280.0, 0.85);
        fluid.addTBPfraction("C30+", 0.06, 450.0, 0.91);
        fluid.addComponent("water", 0.05);
        
        fluid.setMixingRule(10);  // CPA mixing rule
        fluid.setMultiPhaseCheck(true);
        
        ThermodynamicOperations ops = new ThermodynamicOperations(fluid);
        
        System.out.println("========== FLOW ASSURANCE SCREENING ==========");
        System.out.println();
        
        // === 1. HYDRATE SCREENING ===
        System.out.println("--- HYDRATE RISK ---");
        try {
            fluid.setTemperature(280.0);  // 7°C - subsea temperature
            fluid.setPressure(150.0);     // Pipeline pressure
            ops.hydrateFormationTemperature();
            double hydrateT = fluid.getTemperature("C");
            System.out.printf("Hydrate formation temperature at 150 bara: %.1f °C%n", hydrateT);
            
            if (hydrateT > 4.0) {
                System.out.println("⚠️  HIGH HYDRATE RISK - Inhibition required");
            } else {
                System.out.println("✅ Low hydrate risk at seabed temperature");
            }
        } catch (Exception e) {
            System.out.println("Could not calculate hydrate temperature");
        }
        System.out.println();
        
        // === 2. WAX SCREENING ===
        System.out.println("--- WAX RISK ---");
        try {
            ops.calcWAT();
            double waxT = fluid.getWAT("C");
            System.out.printf("Wax Appearance Temperature (WAT): %.1f °C%n", waxT);
            
            if (waxT > 20.0) {
                System.out.println("⚠️  HIGH WAX RISK - Pigging/inhibition needed");
            } else if (waxT > 4.0) {
                System.out.println("⚠️  MODERATE WAX RISK - Monitor");
            } else {
                System.out.println("✅ Low wax risk");
            }
        } catch (Exception e) {
            System.out.println("WAT calculation not available - check C20+ content");
        }
        System.out.println();
        
        // === 3. ASPHALTENE SCREENING (De Boer) ===
        System.out.println("--- ASPHALTENE RISK ---");
        double reservoirP = 350.0;  // bara
        double bubblePointP = 180.0;  // bara (estimate)
        double asphalteneContent = 2.5;  // wt%
        double apiGravity = 32.0;
        
        // De Boer screening criterion
        double deltaP = reservoirP - bubblePointP;
        double deBoerRisk = deltaP * asphalteneContent / 100.0;
        
        System.out.printf("Reservoir pressure: %.0f bara%n", reservoirP);
        System.out.printf("Bubble point: %.0f bara%n", bubblePointP);
        System.out.printf("ΔP (supersaturation): %.0f bar%n", deltaP);
        System.out.printf("De Boer risk parameter: %.2f%n", deBoerRisk);
        
        if (apiGravity > 40 && deltaP > 200) {
            System.out.println("⚠️  HIGH ASPHALTENE RISK - Light oil with high supersaturation");
        } else if (deBoerRisk > 1.5) {
            System.out.println("⚠️  MODERATE ASPHALTENE RISK");
        } else {
            System.out.println("✅ Low asphaltene risk");
        }
        System.out.println();
        
        // === 4. SCALE SCREENING ===
        System.out.println("--- SCALE RISK (Qualitative) ---");
        double co2Content = fluid.getComponent("CO2").getx() * 100;
        double h2sContent = fluid.getComponent("H2S").getx() * 100;
        double waterCut = fluid.getComponent("water").getx() * 100;
        
        System.out.printf("CO2 content: %.2f mol%%%n", co2Content);
        System.out.printf("H2S content: %.3f mol%%%n", h2sContent);
        System.out.printf("Water content: %.1f mol%%%n", waterCut);
        
        if (co2Content > 2.0 && waterCut > 5.0) {
            System.out.println("⚠️  CARBONATE SCALE RISK - CO2 + water present");
        }
        if (h2sContent > 0.01) {
            System.out.println("⚠️  SULFIDE SCALE RISK - H2S present");
        }
        System.out.println();
        
        // === 5. CORROSION SCREENING ===
        System.out.println("--- CORROSION RISK ---");
        if (co2Content > 0.5 && waterCut > 1.0) {
            System.out.println("⚠️  CO2 CORROSION RISK - Sweet corrosion");
        }
        if (h2sContent > 0.001) {
            System.out.println("⚠️  H2S CORROSION RISK - Sour service materials required");
        }
        System.out.println();
        
        // === 6. pH STABILIZATION CHECK ===
        System.out.println("--- pH STABILIZATION ---");
        if (co2Content > 0.5 && waterCut > 1.0) {
            System.out.println("💡 Consider pH stabilization (NaOH) to form protective FeCO3 layer");
            System.out.println("   Target pH: 6.0-6.5 for optimal siderite protection");
            System.out.println("   Use Electrolyte CPA EoS for detailed calculations");
        }
        System.out.println();
        
        // === SUMMARY ===
        System.out.println("========== SCREENING SUMMARY ==========");
        System.out.println("Use detailed models for high-risk areas");
        System.out.println("See individual flow assurance guides for mitigation");
    }
}

Corrosion Control and pH Stabilization

CO2 corrosion (sweet corrosion) is a major flow assurance challenge. NeqSim’s Electrolyte CPA EoS enables sophisticated corrosion control modeling.

pH Stabilization Strategy

pH stabilization uses NaOH to:

  1. Raise aqueous pH above 6.0-6.5
  2. Promote FeCO3 (siderite) protective layer on steel
  3. Reduce corrosion rates by 1-2 orders of magnitude

The siderite protective layer forms when:

\[\text{Fe}^{2+} + \text{CO}_3^{2-} \rightarrow \text{FeCO}_3 \downarrow\]

Quick pH Calculation

import neqsim.thermo.system.SystemElectrolyteCPAstatoil;
import neqsim.thermodynamicoperations.ThermodynamicOperations;

// Create electrolyte system
SystemElectrolyteCPAstatoil fluid = new SystemElectrolyteCPAstatoil(353.15, 50.0);

// Add gas and aqueous components
fluid.addComponent("methane", 0.85);
fluid.addComponent("CO2", 0.03);
fluid.addComponent("water", 0.10);
fluid.addComponent("Na+", 0.01);    // With NaOH treatment
fluid.addComponent("OH-", 0.005);   // Hydroxide from NaOH
fluid.addComponent("Cl-", 0.005);
fluid.addComponent("Fe++", 0.00002);
fluid.addComponent("HCO3-", 0.002);

// Initialize and flash
fluid.chemicalReactionInit();
fluid.createDatabase(true);
fluid.setMixingRule(10);  // Electrolyte mixing rule

ThermodynamicOperations ops = new ThermodynamicOperations(fluid);
ops.TPflash();
fluid.init(3);

// Get pH and check FeCO3 saturation
int aqPhase = fluid.getPhaseNumberOfPhase("aqueous");
double pH = fluid.getPhase(aqPhase).getpH();
System.out.printf("Aqueous pH: %.2f%n", pH);

// Check scale/protective layer potential
ops.checkScalePotential(aqPhase);

FeCO3 Protection Criteria

Factor Optimal Range Notes
pH 6.0-6.5 Higher promotes carbonate layer
Temperature > 60°C Faster scale kinetics
Fe++ concentration 1-10 mg/L Required for layer formation
FeCO3 saturation ratio 1-10 SR > 1 required for precipitation
Flow velocity < 3 m/s Avoid erosion of layer

📚 See pH Stabilization and Corrosion Control for comprehensive documentation including NaOH dosing calculations, combined MEG/pH stabilization for subsea systems, and corrosion rate estimation.

Hydrate Prediction Details

Hydrate Equilibrium Curve

import neqsim.thermo.system.SystemSrkCPAstatoil;
import neqsim.thermodynamicoperations.ThermodynamicOperations;

// Generate hydrate curve
SystemSrkCPAstatoil fluid = new SystemSrkCPAstatoil(273.15, 50.0);
fluid.addComponent("methane", 0.80);
fluid.addComponent("ethane", 0.10);
fluid.addComponent("propane", 0.05);
fluid.addComponent("CO2", 0.03);
fluid.addComponent("water", 0.02);
fluid.setMixingRule(10);
fluid.setHydrateCheck(true);

ThermodynamicOperations ops = new ThermodynamicOperations(fluid);

System.out.println("Pressure (bara) | Hydrate T (°C)");
System.out.println("----------------|---------------");

double[] pressures = {10, 20, 50, 100, 150, 200, 300, 400};
for (double p : pressures) {
    fluid.setPressure(p);
    try {
        ops.hydrateFormationTemperature();
        double hydrateT = fluid.getTemperature("C");
        System.out.printf("%15.0f | %13.1f%n", p, hydrateT);
    } catch (Exception e) {
        System.out.printf("%15.0f | No hydrate%n", p);
    }
}

With Inhibitor

// Add MEG inhibitor
double megConcentration = 0.30;  // 30 wt% in water phase
fluid.addComponent("MEG", megConcentration * 0.02);  // Adjust water amount
fluid.setComponent("water", (1 - megConcentration) * 0.02);

// Recalculate - hydrate T will be depressed
ops.hydrateFormationTemperature();
double inhibitedT = fluid.getTemperature("C");
System.out.printf("Hydrate T with 30%% MEG: %.1f °C%n", inhibitedT);

Wax Modeling

Wax Appearance Temperature (WAT)

import neqsim.thermo.system.SystemSrkEos;
import neqsim.thermodynamicoperations.ThermodynamicOperations;

// Waxy crude - need heavy paraffins
SystemSrkEos fluid = new SystemSrkEos(323.15, 50.0);
fluid.addComponent("methane", 0.20);
fluid.addComponent("n-hexane", 0.10);
fluid.addComponent("n-heptane", 0.10);
fluid.addComponent("n-octane", 0.10);
fluid.addTBPfraction("C10", 0.15, 142.0, 0.78);
fluid.addTBPfraction("C15", 0.15, 212.0, 0.82);
fluid.addTBPfraction("C20", 0.10, 282.0, 0.85);
fluid.addTBPfraction("C25+", 0.10, 350.0, 0.87);
fluid.setMixingRule("classic");

// Enable wax calculations
fluid.setSolidPhaseCheck(true);

ThermodynamicOperations ops = new ThermodynamicOperations(fluid);
ops.calcWAT();

double wat = fluid.getWAT("C");
System.out.printf("Wax Appearance Temperature: %.1f °C%n", wat);

// Wax content vs temperature
System.out.println("\nTemperature (°C) | Wax Content (wt%)");
for (double t = wat; t >= wat - 30; t -= 5) {
    fluid.setTemperature(t + 273.15);
    ops.TPSolidflash();
    double waxWt = fluid.getWaxContent() * 100;
    System.out.printf("%16.0f | %15.2f%n", t, waxWt);
}

Asphaltene Stability

CPA-Based Asphaltene Model

import neqsim.thermo.system.SystemSrkCPAstatoil;
import neqsim.thermodynamicoperations.ThermodynamicOperations;

// Configure for asphaltene calculations
SystemSrkCPAstatoil fluid = new SystemSrkCPAstatoil(373.15, 300.0);

// Light ends
fluid.addComponent("methane", 0.35);
fluid.addComponent("ethane", 0.08);
fluid.addComponent("propane", 0.05);
fluid.addComponent("n-butane", 0.03);

// Oil fractions
fluid.addTBPfraction("C7", 0.10, 95.0, 0.72);
fluid.addTBPfraction("C15", 0.15, 210.0, 0.82);
fluid.addTBPfraction("C30", 0.15, 420.0, 0.89);

// Asphaltene pseudo-component (high MW, high density)
fluid.addTBPfraction("Asphaltene", 0.09, 1000.0, 1.10);

fluid.setMixingRule(10);
fluid.setMultiPhaseCheck(true);

ThermodynamicOperations ops = new ThermodynamicOperations(fluid);

// Check stability at different pressures (depletion path)
System.out.println("Pressure (bara) | Asphaltene Stable?");
System.out.println("----------------|-------------------");

double[] pressures = {300, 250, 200, 180, 160, 140, 120, 100};
for (double p : pressures) {
    fluid.setPressure(p);
    ops.TPflash();
    
    // Check if asphaltene-rich phase forms
    int nPhases = fluid.getNumberOfPhases();
    String stability = (nPhases > 2) ? "⚠️ UNSTABLE" : "✅ Stable";
    System.out.printf("%15.0f | %s%n", p, stability);
}

Asphaltene Onset Pressure

// Find pressure where asphaltenes first precipitate
try {
    ops.asphalteneOnsetPressure();
    double aop = fluid.getPressure("bara");
    System.out.printf("Asphaltene Onset Pressure (AOP): %.1f bara%n", aop);
} catch (Exception e) {
    System.out.println("Could not determine AOP");
}

Combined Operating Envelope

Plot the operating envelope showing all constraints:

import java.util.ArrayList;
import java.util.List;

// Calculate all constraint curves
List<double[]> hydratesCurve = new ArrayList<>();
List<double[]> waxCurve = new ArrayList<>();
double[] aopLine;

// 1. Hydrate equilibrium curve
for (double p = 10; p <= 300; p += 10) {
    fluid.setPressure(p);
    try {
        ops.hydrateFormationTemperature();
        hydratesCurve.add(new double[]{fluid.getTemperature("C"), p});
    } catch (Exception e) {}
}

// 2. WAT line (vertical - temperature independent of pressure to first order)
double wat = 35.0;  // From WAT calculation

// 3. AOP line (horizontal - pressure independent of T to first order)
double aop = 150.0;  // From AOP calculation

// Print operating envelope
System.out.println("========== OPERATING ENVELOPE ==========");
System.out.println();
System.out.println("Safe operating region:");
System.out.printf("  - Temperature > %.1f °C (hydrate limit at operating P)%n", 15.0);
System.out.printf("  - Temperature > %.1f °C (wax limit)%n", wat);
System.out.printf("  - Pressure > %.0f bara (asphaltene onset)%n", aop);
System.out.println();
System.out.println("Or use inhibition/insulation to expand envelope");

Mitigation Strategies

Hydrate Prevention

Strategy Description NeqSim Support
MEG Injection Thermodynamic inhibitor ✅ Full
Methanol Injection Thermodynamic inhibitor ✅ Full
Insulation Keep T above hydrate curve Pipeline models
LDHI Low-dosage hydrate inhibitors ❌ Not modeled
Depressurization Emergency blowdown ✅ Full

Wax Prevention

Strategy Description NeqSim Support
Pigging Mechanical removal ❌ Not modeled
Hot oil circulation Thermal Pipeline models
Pour point depressants Chemical ❌ Not modeled
Insulation Keep T above WAT Pipeline models

Asphaltene Prevention

Strategy Description NeqSim Support
Pressure maintenance Stay above AOP ✅ Full
Chemical dispersants Prevent aggregation ❌ Not modeled
Blending Dilute with light oil ✅ Mixing

Pipeline Temperature Profile

For realistic screening, calculate temperature along the pipeline:

import neqsim.process.equipment.pipeline.PipeBeggsAndBrills;

// Create pipeline
PipeBeggsAndBrills pipeline = new PipeBeggsAndBrills("Subsea Pipeline", wellStream);
pipeline.setLength(50000.0);     // 50 km
pipeline.setDiameter(0.3048);    // 12 inch
pipeline.setOuterTemperature(4.0, "C");  // Seabed temp
pipeline.setRoughness(1.5e-5);

// Get temperature at outlet
pipeline.run();
double outletT = pipeline.getOutletStream().getTemperature("C");

// Compare with hydrate temperature at outlet pressure
double outletP = pipeline.getOutletStream().getPressure("bara");
fluid.setPressure(outletP);
ops.hydrateFormationTemperature();
double hydrateT = fluid.getTemperature("C");

System.out.printf("Pipeline outlet: T=%.1f°C, P=%.1f bara%n", outletT, outletP);
System.out.printf("Hydrate temperature: %.1f°C%n", hydrateT);

if (outletT < hydrateT) {
    System.out.println("⚠️ HYDRATE RISK at pipeline outlet!");
}

See Also