pyResToolbox MCP Server

Calculate gas specific gravity from composition.

COMPOSITIONAL GAS CHARACTERIZATION - Computes gas specific gravity from hydrocarbon molecular weight and non-hydrocarbon mole fractions. Uses molecular weight weighted average method. Essential when gas composition is known but SG measurement is unavailable or unreliable.

Parameters:

• hc_mw (float, required): Hydrocarbon molecular weight in lb/lbmol. Valid: 10-200. Typical: 16-50. Example: 18.5 for typical natural gas.

• co2 (float, optional, default=0.0): CO2 mole fraction (0-1). Typical: 0-0.20. Example: 0.05 for 5% CO2.

• h2s (float, optional, default=0.0): H2S mole fraction (0-1). Typical: 0-0.05. Example: 0.02 for 2% H2S (sour gas).

• n2 (float, optional, default=0.0): N2 mole fraction (0-1). Typical: 0-0.10. Example: 0.01 for 1% N2.

• h2 (float, optional, default=0.0): H2 mole fraction (0-1). Typical: 0-0.01. Example: 0.0 (rare in natural gas).

Calculation Method: Weighted average based on molecular weights:

• HC fraction: User-provided MW (hc_mw)

• CO2: MW = 44.01 lb/lbmol

• H2S: MW = 34.08 lb/lbmol

• N2: MW = 28.01 lb/lbmol

• H2: MW = 2.02 lb/lbmol

• Air: MW = 28.97 lb/lbmol (reference for SG)

Formula: MW_avg = hc_fraction × hc_mw + co2 × 44.01 + h2s × 34.08 + n2 × 28.01 + h2 × 2.02 SG = MW_avg / 28.97

Typical Hydrocarbon MW:

• Pure methane: 16.04

• Dry gas (C1-C2): 16-18

• Associated gas (C1-C4): 18-25

• Wet gas (C1-C6): 25-35

• Condensate gas: 35-50

Applications:

• Compositional Simulation: Convert composition to SG for black oil models

• Gas Plant Feed: Characterize feed gas from composition analysis

• Sales Gas Specs: Calculate SG for pipeline specifications

• Contaminated Gas: Analyze gas with high non-hydrocarbon content

• Laboratory Data: Convert GC analysis to SG

Non-Hydrocarbon Effects:

• CO2 increases SG (MW=44.01 > air MW=28.97)

• H2S increases SG (MW=34.08 > air MW=28.97)

• N2 slightly decreases SG (MW=28.01 ≈ air MW=28.97)

• H2 significantly decreases SG (MW=2.02 << air MW=28.97)

Returns: Dictionary with:

• gas_specific_gravity (float): Gas SG (dimensionless, air=1)

• composition (dict): Detailed composition breakdown

  • hydrocarbon_fraction: Mole fraction of hydrocarbons

  • hydrocarbon_mw: Provided hydrocarbon MW

  • co2_fraction: CO2 mole fraction

  • h2s_fraction: H2S mole fraction

  • n2_fraction: N2 mole fraction

  • h2_fraction: H2 mole fraction

• method (str): "Molecular weight weighted average"

• units (str): "dimensionless (air=1)"

• inputs (dict): Echo of input parameters

Common Mistakes:

• Using weight fraction instead of mole fraction

• Incorrect hydrocarbon MW (must be average MW of HC fraction)

• Mole fractions don't sum to 1.0 (should sum to 1.0)

• Using component MW instead of mixture MW for hydrocarbons

• Not accounting for all non-hydrocarbon components

Example Usage:

Result: SG ≈ 0.65-0.70 (typical natural gas with 5% CO2, 1% N2).

Note: Mole fractions must sum to 1.0. If only HC fraction is provided, ensure hc_fraction = 1.0 - (co2 + h2s + n2 + h2). Hydrocarbon MW should be the average MW of the hydrocarbon fraction, not individual component MW.