pyResToolbox MCP Server

Calculate gas formation volume factor (Bg).

CRITICAL GAS PVT PROPERTY - Computes ratio of gas volume at reservoir conditions to volume at standard conditions. Bg << 1.0 because gas compresses significantly at reservoir pressure. Essential for material balance, reserve calculations, and production forecasting.

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

Bg Behavior:

• Bg decreases with increasing pressure (gas compresses)

• Bg increases with increasing temperature (gas expands)

• Typical range: 0.001-0.01 rcf/scf at reservoir conditions

• At standard conditions (14.7 psia, 60°F): Bg = 1.0 rcf/scf

Formula: Bg = (Z × T × Psc) / (P × Tsc) = 0.02827 × Z × T / P (field units)

Where:

• Z = gas compressibility factor (from gas_z_factor tool)

• T = reservoir temperature (°R)

• P = reservoir pressure (psia)

• Psc = 14.7 psia, Tsc = 520°R (standard conditions)

Returns: Dictionary with:

• value (float or list): Bg in rcf/scf (matches input p shape)

• method (str): Z-factor method used

• units (str): "rcf/scf"

• 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 Bg (gas FVF) with Bo (oil FVF)

• Temperature in Celsius instead of Fahrenheit

Example Usage:

Result: Bg decreases from ~0.005 rcf/scf at 1000 psia to ~0.002 rcf/scf at 4000 psia.

Note: Bg is inversely proportional to pressure. Always use reservoir conditions, not separator conditions. Account for all non-hydrocarbon components for accuracy.