Reservoir Fluid Classification

This document describes NeqSim’s reservoir fluid classification capabilities using the FluidClassifier utility class based on the Whitson methodology.

Overview

Reservoir fluid classification is essential for selecting appropriate modeling approaches and simulation strategies. NeqSim implements the industry-standard Whitson classification methodology to categorize fluids into:

Classification Criteria

The Whitson classification uses three primary criteria:

Fluid Type GOR (scf/STB) C7+ (mol%) API Gravity
Dry Gas > 100,000 < 0.7 N/A
Wet Gas 15,000 - 100,000 0.7 - 4 40-60°
Gas Condensate 3,300 - 15,000 4 - 12.5 40-60°
Volatile Oil 1,000 - 3,300 12.5 - 20 40-50°
Black Oil < 1,000 > 20 15-40°
Heavy Oil < 200 > 30 10-15°

Basic Usage

Classification by Composition

import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;
import neqsim.thermo.util.FluidClassifier;
import neqsim.thermo.util.ReservoirFluidType;

// Create a fluid
SystemInterface fluid = new SystemSrkEos(373.15, 100.0);
fluid.addComponent("methane", 0.70);
fluid.addComponent("ethane", 0.10);
fluid.addComponent("propane", 0.08);
fluid.addComponent("n-heptane", 0.07);
fluid.addComponent("C10", 0.05);
fluid.createDatabase(true);
fluid.setMixingRule("classic");

// Classify the fluid
ReservoirFluidType type = FluidClassifier.classify(fluid);
System.out.println("Fluid type: " + type.getDisplayName());
// Output: Fluid type: Gas Condensate

Classification by GOR

// Classify directly from GOR measurement
double gorScfStb = 5000.0;  // scf/STB
ReservoirFluidType type = FluidClassifier.classifyByGOR(gorScfStb);
System.out.println("Fluid type: " + type.getDisplayName());
// Output: Fluid type: Gas Condensate

Classification by C7+ Content

// Classify directly from C7+ content
double c7PlusMolPercent = 8.5;  // mol%
ReservoirFluidType type = FluidClassifier.classifyByC7Plus(c7PlusMolPercent);
System.out.println("Fluid type: " + type.getDisplayName());
// Output: Fluid type: Gas Condensate

Advanced Classification

With Phase Envelope Analysis

For more accurate classification, use the phase envelope method which considers:

// Classify using phase envelope analysis
double reservoirTempK = 373.15;  // 100°C
ReservoirFluidType type = FluidClassifier.classifyWithPhaseEnvelope(fluid, reservoirTempK);
System.out.println("Fluid type: " + type.getDisplayName());

Calculating C7+ Content

// Calculate C7+ content for any fluid
double c7Plus = FluidClassifier.calculateC7PlusContent(fluid);
System.out.println("C7+ content: " + c7Plus + " mol%");

Estimating API Gravity

// Estimate API gravity from fluid composition
double apiGravity = FluidClassifier.estimateAPIGravity(fluid);
if (!Double.isNaN(apiGravity)) {
    System.out.println("Estimated API gravity: " + apiGravity + "°");
}

Classification Report

Generate a comprehensive classification report:

String report = FluidClassifier.generateClassificationReport(fluid);
System.out.println(report);

Output:

=== Reservoir Fluid Classification Report ===

Composition Analysis:
  C7+ Content: 12.00 mol%

Classification Result:
  Fluid Type: Gas Condensate
  Typical GOR Range: 3,300 - 15,000 scf/STB
  Typical C7+ Range: 4 - 12.5 mol%

  Estimated API Gravity: 48.5°

Modeling Recommendations:
  - Compositional simulation recommended
  - CVD experiment important for liquid dropout curve
  - Consider modified black-oil with OGR (Rv)

ReservoirFluidType Enum

The ReservoirFluidType enum provides detailed information for each fluid type:

ReservoirFluidType type = ReservoirFluidType.GAS_CONDENSATE;

// Get display name
String name = type.getDisplayName();  // "Gas Condensate"

// Get typical ranges
String gorRange = type.getTypicalGORRange();  // "3,300 - 15,000"
String c7PlusRange = type.getTypicalC7PlusRange();  // "4 - 12.5"

Available Fluid Types

Enum Value Display Name Description
DRY_GAS Dry Gas No liquid dropout
WET_GAS Wet Gas Surface liquid only
GAS_CONDENSATE Gas Condensate Retrograde condensation
VOLATILE_OIL Volatile Oil High shrinkage oil
BLACK_OIL Black Oil Conventional crude
HEAVY_OIL Heavy Oil High viscosity crude
UNKNOWN Unknown Unclassified

Python Usage

from jpype import JClass

# Import classes
FluidClassifier = JClass('neqsim.thermo.util.FluidClassifier')
ReservoirFluidType = JClass('neqsim.thermo.util.ReservoirFluidType')
SystemSrkEos = JClass('neqsim.thermo.system.SystemSrkEos')

# Create fluid
fluid = SystemSrkEos(373.15, 100.0)
fluid.addComponent("methane", 0.70)
fluid.addComponent("ethane", 0.10)
fluid.addComponent("n-heptane", 0.12)
fluid.addComponent("C10", 0.08)
fluid.createDatabase(True)
fluid.setMixingRule("classic")

# Classify
fluid_type = FluidClassifier.classify(fluid)
print(f"Fluid type: {fluid_type.getDisplayName()}")

# Get C7+ content
c7plus = FluidClassifier.calculateC7PlusContent(fluid)
print(f"C7+ content: {c7plus:.2f} mol%")

# Generate report
report = FluidClassifier.generateClassificationReport(fluid)
print(report)

Modeling Recommendations by Fluid Type

Dry Gas and Wet Gas

Gas Condensate

Volatile Oil

Black Oil

Heavy Oil

Implementation Details

C7+ Detection Algorithm

The calculateC7PlusContent method identifies C7+ components by:

  1. Molar mass ≥ 100 g/mol
  2. Component name starting with C7, C8, C9, etc.
  3. Component name containing “heptane”, “octane”, “nonane”, “decane”
  4. Components flagged as TBP fractions (isIsTBPfraction())
  5. Components flagged as plus fractions (isIsPlusFraction())

Phase Envelope Classification

The classifyWithPhaseEnvelope method refines composition-based classification by:

  1. Calculating the critical point using phase envelope algorithm
  2. Comparing reservoir temperature to critical temperature
  3. Adjusting classification if reservoir T is near or above Tc

References

API Reference

FluidClassifier Class

Method Parameters Returns Description
classify SystemInterface fluid ReservoirFluidType Classify by composition
classifyByGOR double gorScfStb ReservoirFluidType Classify by GOR
classifyByC7Plus double c7PlusMolPercent ReservoirFluidType Classify by C7+ content
classifyWithPhaseEnvelope SystemInterface fluid, double reservoirTemperatureK ReservoirFluidType Classify with phase envelope
calculateC7PlusContent SystemInterface fluid double Calculate C7+ content (mol%)
estimateAPIGravity SystemInterface fluid double Estimate API gravity
generateClassificationReport SystemInterface fluid String Generate full report

ReservoirFluidType Enum

Method Returns Description
getDisplayName() String Human-readable fluid type name
getTypicalGORRange() String Typical GOR range string
getTypicalC7PlusRange() String Typical C7+ range string

See Also