Produced Water Degassing System

High-level model for produced water degassing with greenhouse gas emission calculations.

Table of Contents

Overview

Location: neqsim.process.equipment.util.ProducedWaterDegassingSystem

The ProducedWaterDegassingSystem class models multi-stage degassing for produced water treatment, automatically calculating greenhouse gas emissions at each stage. This is based on the methodology from the GFMW 2023 paper “Virtual Measurement of Emissions from Produced Water Using an Online Process Simulator”.

Key Features

Regulatory Context

This implementation supports compliance with:

Regulation Description
Aktivitetsforskriften §70 Measurement and calculation requirements
Norwegian Offshore Emission Handbook Replaces conventional solubility factor method
Norwegian Environment Agency Annual emission reporting

Comparison: Virtual vs Conventional Methods

Aspect Conventional Method Virtual Measurement
Gas solubility Fixed factors (ppmv/bar) CPA-EoS calculation
Composition Assumed (often 100% CH₄) Component-by-component
Accuracy ±30-50% typical ±3.6% total gas
Calibration None Lab-tuned kij parameters

Thermodynamic Model

CPA Equation of State

Uses SRK-CPA (Cubic Plus Association) with:

Binary Interaction Parameters (Tuned)

Pair kij Base kij Temp Coeff Source
Water-CO₂ -0.24 0.001121 Kristiansen 2023
Water-CH₄ -0.72 0.002605 Kristiansen 2023
Water-C₂H₆ 0.11 - Literature
Water-C₃H₈ 0.205 - Literature

Model Validation

Validated against produced water samples from high-CO₂ reservoirs:

Process Description

Typical 3-Stage System

Water from ────►  Degasser  ────►    CFU    ────►  Caisson  ────► Sea
Separator        (3-5 barg)       (1 barg)        (atm)
                     │                │               │
                     ▼                ▼               ▼
               Gas to Flare    Gas to Vent    Gas to Atmosphere

Stage Details

Stage Pressure Temperature Emissions Destination
Degasser 3-5 barg 60-80°C Flare/fuel gas
CFU 1.0 barg 40-60°C Atmospheric vent
Caisson 1.01 bara Ambient Direct to atmosphere

Usage Examples

Java Example - Basic Setup

import neqsim.process.equipment.util.ProducedWaterDegassingSystem;

// Create produced water degassing system
ProducedWaterDegassingSystem system = new ProducedWaterDegassingSystem("Platform PW");

// Set water flow conditions
system.setWaterFlowRate(100.0, "m3/hr");      // Produced water rate
system.setWaterTemperature(80.0, "C");        // From separator
system.setInletPressure(30.0, "bara");        // Upstream pressure

// Set stage pressures
system.setDegasserPressure(4.0, "bara");
system.setCFUPressure(1.0, "bara");
// Caisson is atmospheric by default

// Set dissolved gas composition (from PVT analysis)
system.setDissolvedGasComposition(
    new String[]{"CO2", "methane", "ethane", "propane"},
    new double[]{0.51, 0.44, 0.04, 0.01}  // Mole fractions
);

// Optional: Use tuned kij parameters from lab calibration
system.setTunedInteractionParameters(true);

// Set salinity if known
system.setSalinity(10.0, "wt%");  // 10 wt% NaCl

// Run calculation
system.run();

// Get emissions report
System.out.println(system.getEmissionsReport());

Python Example

from neqsim import jneqsim

ProducedWaterDegassingSystem = jneqsim.process.equipment.util.ProducedWaterDegassingSystem

# Create degassing system
system = ProducedWaterDegassingSystem("Platform PW")

# Configure
system.setWaterFlowRate(100.0, "m3/hr")
system.setWaterTemperature(80.0, "C")
system.setInletPressure(30.0, "bara")

# Set stage pressures
system.setDegasserPressure(4.0, "bara")
system.setCFUPressure(1.0, "bara")

# Set dissolved gas (typical Gudrun composition)
components = ["CO2", "methane", "ethane", "propane"]
fractions = [0.51, 0.44, 0.04, 0.01]
for comp, frac in zip(components, fractions):
    system.addDissolvedComponent(comp, frac)

# Use tuned parameters
system.setTunedInteractionParameters(True)

# Run
system.run()

# Get results
print(system.getEmissionsReport())
print(f"\nTotal emissions: {system.getTotalEmissionsTonnesCO2eq():.2f} tonnes CO2eq/year")

Detailed Emission Results

// Get emissions by stage
double degasserCH4 = system.getDegasserEmissions().getCH4("kg/hr");
double degasserCO2 = system.getDegasserEmissions().getCO2("kg/hr");

double cfuCH4 = system.getCFUEmissions().getCH4("kg/hr");
double cfuCO2 = system.getCFUEmissions().getCO2("kg/hr");

double caissonCH4 = system.getCaissonEmissions().getCH4("kg/hr");
double caissonCO2 = system.getCaissonEmissions().getCO2("kg/hr");

// Total GWP (Global Warming Potential)
double totalCO2eq = system.getTotalEmissionsTonnesCO2eq();  // tonnes/year

System.out.println("Stage Emissions (kg/hr):");
System.out.printf("  Degasser: CH4=%.2f, CO2=%.2f%n", degasserCH4, degasserCO2);
System.out.printf("  CFU:      CH4=%.2f, CO2=%.2f%n", cfuCH4, cfuCO2);
System.out.printf("  Caisson:  CH4=%.2f, CO2=%.2f%n", caissonCH4, caissonCO2);
System.out.printf("Total GHG: %.1f tonnes CO2eq/year%n", totalCO2eq);

Emission Calculations

Gas Water Ratio (GWR)

The model calculates the Gas Water Ratio at each stage:

\[GWR = \frac{V_{gas}}{V_{water}}\]

Where:

CO₂ Equivalent Emissions

Total emissions in CO₂ equivalent:

\[E_{CO_2eq} = E_{CO_2} + GWP_{CH_4} \times E_{CH_4} + GWP_{NMVOC} \times E_{NMVOC}\]

Where:

Comparison with Handbook Method

// Get method comparison
String comparison = system.getMethodComparisonReport();
System.out.println(comparison);

// Typical output:
// Method Comparison (kg CH4/hr):
//   Virtual measurement: 12.5
//   Handbook method:     18.2
//   Difference:          -31%

Calibration and Validation

Lab Calibration

For improved accuracy, calibrate against lab measurements:

// Set lab-measured Gas Water Ratio for calibration
system.setLabGWR(0.15, "Sm3/m3");  // Measured at lab conditions

// Set lab gas composition (mole fractions)
system.setLabGasComposition(new String[]{"CO2", "methane"}, 
                            new double[]{0.52, 0.45});

// Enable tuned parameters
system.setTunedInteractionParameters(true);

// Run and compare
system.run();

double modelGWR = system.getCalculatedGWR();
double labGWR = system.getLabGWR();
double deviation = Math.abs((modelGWR - labGWR) / labGWR * 100);

System.out.printf("Model vs Lab: %.1f%% deviation%n", deviation);

Online Calibration

For real-time virtual metering:

// Update with process measurements
system.setActualWaterFlowRate(measuredFlow);
system.setActualTemperature(measuredTemp);
system.setActualPressures(degasserP, cfuP);

// Recalculate
system.run();

// Get updated emissions
double currentEmissions = system.getCurrentEmissionsRate("kg/hr");

API Reference

Constructors

Constructor Description
ProducedWaterDegassingSystem(String name) Create system with name

Configuration - Flow Conditions

Method Description
setWaterFlowRate(double, String) Set water flow (kg/hr, m3/hr, bbl/day)
setWaterTemperature(double, String) Set temperature (C, K, F)
setInletPressure(double, String) Set upstream pressure (bara, barg)
setSalinity(double, String) Set water salinity (wt%)

Configuration - Stage Pressures

Method Description
setDegasserPressure(double, String) Set degasser pressure
setCFUPressure(double, String) Set CFU pressure
setCaissonPressure(double, String) Set caisson pressure (default atmospheric)

Configuration - Composition

Method Description
setDissolvedGasComposition(String[], double[]) Set gas composition
addDissolvedComponent(String, double) Add single component
clearDissolvedComponents() Clear composition

Configuration - Model

Method Description
setTunedInteractionParameters(boolean) Use tuned kij values
setLabGWR(double, String) Set lab-measured GWR
setLabGasComposition(String[], double[]) Set lab gas composition

Results - Emissions

Method Description
getDegasserEmissions() Get EmissionsCalculator for degasser
getCFUEmissions() Get EmissionsCalculator for CFU
getCaissonEmissions() Get EmissionsCalculator for caisson
getTotalEmissionsTonnesCO2eq() Get total GHG (tonnes CO2eq/year)
getEmissionsReport() Get formatted emissions report

Results - Gas Data

Method Description
getCalculatedGWR() Get calculated Gas Water Ratio
getTotalGasLiberated() Get total gas volume (Sm³/hr)
getMethodComparisonReport() Compare virtual vs handbook methods

Results - Process

Method Description
getDegasserOutlet() Get degasser water outlet stream
getCFUOutlet() Get CFU water outlet stream
toJson() Get full results as JSON