oil_compressibility
Calculate oil compressibility coefficient to measure volume changes with pressure for material balance calculations, pressure transient analysis, and reserve estimation in petroleum engineering.
Instructions
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:
{
"p": [2000, 3000, 4000],
"api": 35.0,
"degf": 180.0,
"pb": 3500.0,
"sg_g": 0.75,
"rs": [400, 600, 800],
"rsb": 800.0
}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.
Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| request | Yes |
Output Schema
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||