pyResToolbox MCP Server

Calculate gas specific gravity from pressure gradient.

DIAGNOSTIC TOOL - Determines gas specific gravity from measured pressure gradient in a gas column. Uses standalone Newton-Raphson solver (fixed implementation) to solve the inverse problem. Essential for formation fluid identification and gas property verification when only gradient data is available.

Parameters:

• gradient (float, required): Pressure gradient in psi/ft. Must be > 0. Typical: 0.05-0.15 psi/ft. Example: 0.1 psi/ft.

• degf (float, required): Temperature in °F at measurement depth. Valid: -460 to 1000. Typical: 100-400°F. Example: 180.0.

• p (float, required): Pressure in psia at measurement depth. Must be > 0. Example: 3500.0.

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

Gradient Principle: Gas gradient = dP/dh = (ρg × g) / 144 = (P × MW) / (Z × R × T × 144)

Where:

• ρg = gas density (lb/cuft)

• 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)

Applications:

• Formation Fluid ID: Identify gas vs oil vs water from gradient

• Gas Density Verification: Check measured gas gravity against gradient

• Completion Fluid Design: Design mud weight based on gas gradient

• Wellbore Pressure Modeling: Calculate pressure profiles in gas columns

Typical Gradients:

• Dry gas (sg=0.6): ~0.08 psi/ft

• Associated gas (sg=0.8): ~0.11 psi/ft

• Heavy gas (sg=1.0): ~0.14 psi/ft

Solution Method: Uses Newton-Raphson iterative solver to find sg that yields the specified gradient. This is a standalone fixed implementation that avoids upstream library bugs.

Returns: Dictionary with:

• value (float): Gas specific gravity (dimensionless, air=1)

• method (str): "Gradient correlation (Newton-Raphson)"

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

• 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 (affects MW and Z)

• Using wrong gradient units (must be psi/ft, not psi/100ft)

• Temperature in Celsius instead of Fahrenheit

Example Usage:

Result: Gas SG ≈ 0.7-0.8 for typical natural gas gradient.

Note: This tool uses a standalone fixed implementation to avoid upstream bugs. Always use reservoir conditions (pressure and temperature at measurement depth). Gradient is sensitive to temperature - use correct temperature for accurate results.