NeqSim vs Norwegian Handbook: Emission Calculation Methods Comparison

📖 Related Documentation:

Produced Water Emissions Tutorial - Complete implementation guide

Examples Index - All tutorials and examples

REFERENCE_MANUAL_INDEX - Chapter 43 - Full API documentation

Overview

This document compares the conventional Norwegian handbook method for emission reporting with the NeqSim thermodynamic method implemented via NeqSimLive. The comparison is based on the methodology presented in:

“Virtual Measurement of Emissions from Produced Water Using an Online Process Simulator”
Kristiansen et al., Global Flow Measurement Workshop (GFMW), October 2023
Full paper available in docs/GFMW_2023_Emissions_Paper.txt

Norwegian Continental Shelf Emissions Context

Regulatory Framework

The Norwegian Continental Shelf (NCS) is one of the world’s most strictly regulated offshore petroleum provinces:

Metric	NCS Statistics (2024)
Total GHG emissions	~10.9 million tonnes CO₂eq
Share of Norway’s total GHG	~25%
nmVOC emissions	~21,500 tonnes
Carbon tax + EU ETS cost	~NOK 1,565/tonne CO₂
Total annual emission cost	~NOK 16 billion

Source: Norwegian Petroleum - Emissions to Air

Key Regulations

Aktivitetsforskriften §70 (Activities Regulations): Operators must measure or calculate emissions with quality-assured, representative methods
Norwegian Offshore Emission Handbook: Defines conventional calculation factors
CO₂ Tax Act on Petroleum Activities: Carbon pricing mechanism
EU ETS: Emissions trading system participation

Method Comparison

1. Norwegian Handbook Method (Conventional)

Reference: Håndbok for kvantifisering av direkte metan- og nmVOC-utslipp (Retningslinje 044)

Formulas

U_CH4 = f_CH4 × V_pw × ΔP × 10⁻⁶  [tonnes/year]
U_NMVOC = f_NMVOC × V_pw × ΔP × 10⁻⁶  [tonnes/year]

Parameters

Parameter	Symbol	Value	Unit
Methane solubility factor	f_CH4	14	g/(m³·bar)
nmVOC solubility factor	f_NMVOC	3.5	g/(m³·bar)
Produced water volume	V_pw	varies	m³/year
Pressure drop	ΔP	varies	bar

Limitations

Issue	Impact
CO₂ not included	Misses 72-78% of total gas emissions
Fixed factors	Cannot reflect real process conditions
No temperature dependence	Same factor for 50°C and 100°C
No salinity correction	Same factor for fresh and saline water
No composition dependence	Same factor regardless of gas composition
Uncertainty	Estimated ±50% or higher

2. NeqSim Thermodynamic Method

Thermodynamic Model

Equation of State: SRK-CPA (Cubic Plus Association)

The CPA-EoS extends the traditional cubic equation of state with an association term for polar molecules:

P = P_physical + P_association

Where:

P_physical: SRK equation for non-polar interactions
P_association: Wertheim’s perturbation theory for hydrogen bonding (water, glycols)

Mixing Rule

Uses mixing rule 10 with electrolyte correction for saline produced water (NaCl content).

Binary Interaction Parameters (kij)

Tuned parameters from laboratory validation (Kristiansen et al., 2023):

System	kij Formula	Temperature Range
Water-CO₂	kij = -0.24 + 0.001121 × T(°C)	50-100°C
Water-CH₄	kij = -0.72 + 0.002605 × T(°C)	50-100°C
Water-C₂H₆	kij = 0.11 (fixed)	All
Water-C₃H₈	kij = 0.205 (fixed)	All

Implementation in NeqSim

// Create system with CPA-EoS
SystemSrkCPAstatoil fluid = new SystemSrkCPAstatoil(273.15 + 80, 65.0);
fluid.addComponent("water", 0.85);
fluid.addComponent("CO2", 0.03);
fluid.addComponent("methane", 0.08);
fluid.addComponent("ethane", 0.02);
fluid.addComponent("propane", 0.01);
fluid.addComponent("n-butane", 0.005);
fluid.addComponent("Na+", 0.002);
fluid.addComponent("Cl-", 0.003);

// CPA mixing rule for water-hydrocarbon systems
fluid.setMixingRule(10);
fluid.setMultiPhaseCheck(true);

Advantages

Feature	Benefit
Includes CO₂	Captures all emission components
Process conditions	Reflects actual P, T variations
Salinity effects	“Salting-out” reduces gas solubility
Composition-based	Uses actual well stream PVT data
Real-time capable	Live connection to process data
Validated uncertainty	±3.6% total gas, ±7.4% methane

Validation Results (Gudrun Field)

Case Study Parameters

Parameter	Value
Field	Gudrun (North Sea)
Water salinity	10-11 wt% NaCl
Temperature	75-90°C
Separator pressure	65 bara typical
Degasser pressure	3-5 barg
CFU pressure	0.2-1 barg
Validation period	2020-2023

Comparison with Field Measurements

Metric	NeqSim vs Measurement
GWR (Gas-Water Ratio)	-1% to +4%
CO₂ composition	±1%
CH₄ composition	±1%
Total gas mass rate	-2% to -7.2% (annual cumulative)
Gas molar mass	Good agreement with USM
Gas density	Good agreement with USM

Emission Comparison (2022 Data)

Method	CH₄ + nmVOC	CO₂	Total Gas	CO₂ Equivalents
Conventional Handbook	100%	0%	Higher	11,000 tonnes
NeqSimLive	22-28%	72-78%	Accurate	4,700 tonnes
Reduction	-	-	-	-58%

Key Finding: CO₂ Dominates Emissions

The NeqSimLive data revealed that 72-78% of emissions are CO₂, not hydrocarbons as assumed by the conventional method. This fundamentally changes emission reporting:

Conventional: All emissions = CH₄ + nmVOC (high GWP)
Reality:      Most emissions = CO₂ (lower GWP)

Solubility Factor Comparison

Component	Handbook Factor	NeqSim Calculated	Difference
Methane	14 g/(m³·bar)	5-6 g/(m³·bar)	-60%
nmVOC	3.5 g/(m³·bar)	1.2-1.4 g/(m³·bar)	-65%
CO₂	Not included	15-30 g/(m³·bar)	Missing!

Implementation Complexity Levels

NeqSim supports various implementation levels depending on process complexity:

Level 1: Simple Calculator

For basic flash calculations without full process modeling:

from neqsim import jNeqSim

# Quick emission estimate from single flash
calc = jNeqSim.process.equipment.util.EmissionsCalculator
ch4 = calc.calculateConventionalCH4(water_volume_m3, pressure_drop_bar)

# Or use thermodynamic flash
fluid = jNeqSim.thermo.system.SystemSrkCPAstatoil(273.15 + 80, 4.0)
# ... configure and flash

Level 2: Multi-Stage Degassing Model

For typical produced water treatment trains:

ProducedWaterDegassingSystem system = new ProducedWaterDegassingSystem("Platform PW");
system.setWaterFlowRate(100.0, "m3/hr");
system.setDegasserPressure(4.0, "bara");
system.setCFUPressure(1.2, "bara");
system.setDissolvedGasComposition(composition);
system.run();

// Get comparison report
System.out.println(system.getMethodComparisonReport());

Level 3: Full Process Plant Model

For complex processes like TEG dehydration with emission tracking:

ProcessSystem process = new ProcessSystem();

// Add all unit operations
Stream feed = new Stream("Feed", feedFluid);
Separator separator = new Separator("HP Sep", feed);
TEGAbsorber absorber = new TEGAbsorber("Contactor");
TEGRegeneration regen = new TEGRegeneration("Regenerator");
// ... configure full process

process.add(feed);
process.add(separator);
process.add(absorber);
process.add(regen);
process.run();

// Track emissions from each source
EmissionsCalculator sepEmissions = new EmissionsCalculator(separator.getGasOutStream());
EmissionsCalculator flashEmissions = new EmissionsCalculator(regen.getStillColumn().getGasOut());

Level 4: NeqSimLive (Real-Time Cloud API)

For production operations with live data integration:

┌─────────────────┐     ┌─────────────────┐     ┌─────────────────┐
│   PI/Aspen      │────▶│   SIGMA         │────▶│   NeqSimAPI     │
│   (Field Data)  │◀────│   (Scheduler)   │◀────│   (Cloud)       │
└─────────────────┘     └─────────────────┘     └─────────────────┘
                                                        │
                                                        ▼
                                                ┌─────────────────┐
                                                │   NeqSim        │
                                                │   (Calculation) │
                                                └─────────────────┘
                                                        │
                        ┌───────────────────────────────┤
                        ▼                               ▼
                ┌─────────────────┐             ┌─────────────────┐
                │  Emisoft        │             │  MPRML          │
                │  (Env. Agency)  │             │  (Tax/NPD)      │
                └─────────────────┘             └─────────────────┘

Key features:

Runs in Microsoft Azure cloud
5-15 minute calculation intervals
Automatic emission reporting to authorities
Supports multiple facilities from single API

Calibration Requirements

Recommended Calibration Frequency

Condition	Frequency
Normal operations	2 samples/year
Well composition change	Immediate recalibration
Back-production of injection water	Immediate recalibration
New wells online	Reassess within 1 month

Required Measurements for Calibration

Pressurized water sample from separator outlet
Single-stage flash to atmospheric conditions (15°C, 1 atm)
Gas chromatography for composition
GWR measurement (Sm³ gas / Sm³ water)
Water salinity analysis (NaCl content)

Validation Criteria

Per Norwegian offshore emission handbook, acceptable uncertainty is ±7.5% for emission gases.

NeqSim achieves:

Total gas: ±3.6%
CO₂: ±3.6%
Methane: ±7.4%
nmVOC: ±38% (higher due to small quantities)

References

Kristiansen, O., et al. (2023). “Virtual Measurement of Emissions from Produced Water Using an Online Process Simulator.” Global Flow Measurement Workshop.
Petroleum Safety Authority Norway. “Activities Regulations, Chapter XI - Emissions and discharges to the external environment, §70 Measurement and calculation.” https://www.ptil.no/en/regulations/
Norwegian Environment Agency. “Håndbok for kvantifisering av direkte metan- og nmVOC-utslipp” (Retningslinje 044).
Søreide, I. & Whitson, C.H. (1992). “Peng-Robinson predictions for hydrocarbons, CO₂, N₂ and H₂S with pure water and NaCl brine.” Fluid Phase Equilibria 77: 217-240.
Kontogeorgis, G.M., et al. (2006). “Ten Years with the CPA Equation of State.” Ind. Eng. Chem. Res. 45: 4869-4878.
Norwegian Petroleum. “Emissions to Air.” https://www.norskpetroleum.no/en/environment-and-technology/emissions-to-air/

Conclusion

The NeqSim thermodynamic method provides significant advantages over the conventional Norwegian handbook method:

Aspect	Handbook	NeqSim
CO₂ emissions	❌ Not captured	✅ Full accounting
Process conditions	❌ Fixed factors	✅ Real-time P, T, composition
Salinity effects	❌ Ignored	✅ Electrolyte model
Uncertainty	±50%+	±3.6%
Automation	❌ Manual annual	✅ Live API (NeqSimLive)
Regulatory compliance	✅ Accepted	✅ More accurate

Key outcome from Gudrun: Reported emissions reduced from 11,000 to 4,700 tonnes CO₂eq (-58%) by using the more accurate thermodynamic method.

For facilities with significant produced water handling, implementing NeqSim-based emission calculations can:

Improve reporting accuracy
Identify actual emission sources
Support emission reduction initiatives
Ensure regulatory compliance with better uncertainty

Document generated from NeqSim emission calculation framework. See ProducedWaterEmissions_Tutorial.md for implementation details.