pyResToolbox MCP Server

Calculate gas viscosity (μg).

CRITICAL GAS PVT PROPERTY - Computes gas viscosity at reservoir conditions using Lee, Gonzalez & Eakin (1966) correlation, industry standard for natural gas. Viscosity affects flow rates, pressure drops, and well performance. Gas viscosity increases with pressure and temperature, opposite to liquid behavior.

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 viscosity calculation. Options: "DAK", "HY", "WYW", "BUR". DAK recommended.

Viscosity Behavior:

• Increases with pressure (gas molecules closer together)

• Increases with temperature (molecular motion increases)

• Typical range: 0.01-0.05 cP at reservoir conditions

• At standard conditions: ~0.01 cP

Lee-Gonzalez-Eakin Correlation: Uses Z-factor internally to account for real gas behavior. More accurate than ideal gas assumptions, especially at high pressures.

Returns: Dictionary with:

• value (float or list): Viscosity in cP (matches input p shape)

• method (str): "Lee-Gonzalez-Eakin"

• units (str): "cP"

• 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

• Confusing gas viscosity (increases with P) with oil viscosity (decreases with P)

• Temperature in Celsius instead of Fahrenheit

Example Usage:

Result: Viscosity increases from ~0.012 cP at 1000 psia to ~0.025 cP at 4000 psia.

Note: Gas viscosity is much lower than oil viscosity (typically 0.01-0.05 cP vs 0.5-10 cP). Always use reservoir conditions, not separator conditions. Account for all non-hydrocarbon components for accuracy.