pyResToolbox MCP Server

Calculate oil compressibility (Co).

CRITICAL PVT PROPERTY - Computes oil compressibility coefficient, which measures how much oil volume changes with pressure. Essential for material balance calculations, pressure transient analysis, and reserve estimation. Co is typically 5-50 × 10⁻⁶ 1/psi.

Parameters:

• p (float or list, required): Pressure(s) in psia. Must be > 0. Can be scalar or array. Example: 3000.0 or [2000, 3000, 4000].

• api (float, required): Oil API gravity in degrees. Valid: 0-100. Example: 35.0.

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

• pb (float, required): Bubble point pressure in psia. Must be ≥ 0. Example: 3500.0.

• sg_g (float, required): Gas specific gravity (air=1). Valid: 0-3. Typical: 0.6-1.2. Example: 0.75.

• rs (float or list, optional, default=0.0): Solution GOR at pressure p in scf/stb. If 0, will be calculated. Must match p shape. Example: 600.0.

• rsb (float, optional, default=0.0): Solution GOR at bubble point in scf/stb. Required if pb provided. Example: 800.0.

Compressibility Behavior:

• p < pb: Co is relatively constant (oil + dissolved gas compressibility)

• p = pb: Co increases sharply (gas evolution begins)

• p > pb: Co decreases with pressure (gas compressibility dominates)

Typical Ranges:

• Undersaturated oil: 5-20 × 10⁻⁶ 1/psi

• At bubble point: 20-50 × 10⁻⁶ 1/psi

• Above bubble point: 10-30 × 10⁻⁶ 1/psi

Returns: Dictionary with:

• value (float or list): Compressibility in 1/psi (matches input p shape)

• method (str): "McCain"

• units (str): "1/psi"

• inputs (dict): Echo of input parameters

Common Mistakes:

• Not providing pb (required for accurate calculation)

• Using wrong pressure (must be reservoir pressure, not separator)

• Confusing oil compressibility with gas compressibility

• Not accounting for dissolved gas effects

Example Usage:

Result: Co ≈ 10-15 × 10⁻⁶ 1/psi below bubble point, increases near pb.

Note: Compressibility is critical for material balance calculations. Always provide pb for accurate results. Co values are small (micro-1/psi), so results are typically in scientific notation.