pyResToolbox MCP Server

Calculate gas density (ρg) at reservoir conditions.

CRITICAL GAS PVT PROPERTY - Computes gas density from real gas equation of state. Essential for gradient calculations, well pressure analysis, and material balance. Gas density increases significantly with pressure due to compressibility.

Parameters:

• sg (float, required): Gas specific gravity (air=1.0). Valid: 0.55-3.0. Typical: 0.6-1.2. Example: 0.7.

• degf (float, required): Reservoir temperature in °F. Valid: -460 to 1000. Typical: 100-400°F. Example: 180.0.

• p (float or list, required): Pressure(s) in psia. Must be > 0. Can be scalar or array. Example: 3500.0 or [1000, 2000, 3000, 4000].

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

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

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

• zmethod (str, optional, default="DAK"): Z-factor method for density calculation. Options: "DAK", "HY", "WYW", "BUR". DAK recommended.

Density Formula: ρg = (P × MW) / (Z × R × T)

Where:

• P = pressure (psia)

• MW = molecular weight = sg × 28.97 lb/lbmol

• Z = gas compressibility factor

• R = gas constant = 10.732 psia·ft³/(lbmol·°R)

• T = temperature (°R = °F + 460)

Density Behavior:

• Increases with pressure (gas compresses)

• Decreases with temperature (gas expands)

• Typical range: 5-20 lb/cuft at reservoir conditions

• At standard conditions: ~0.05-0.1 lb/cuft

Returns: Dictionary with:

• value (float or list): Density in lb/cuft (matches input p shape)

• method (str): Z-factor method used

• units (str): "lb/cuft"

• inputs (dict): Echo of input parameters

Common Mistakes:

• Using separator temperature instead of reservoir temperature

• Pressure in barg/psig instead of psia (must be absolute)

• Not accounting for non-hydrocarbon fractions

• Using ideal gas law (Z=1) instead of real gas (Z<1)

• Temperature in Celsius instead of Fahrenheit

Example Usage:

Result: Density increases from ~8 lb/cuft at 1000 psia to ~18 lb/cuft at 4000 psia.

Note: Gas density is much lower than oil density (typically 5-20 lb/cuft vs 40-60 lb/cuft). Always use reservoir conditions. Account for all non-hydrocarbon components - they significantly affect molecular weight and density.