gas_pseudopressure
Calculate gas pseudopressure difference to linearize gas flow equations, enabling use of liquid flow solutions for accurate gas well performance analysis and reservoir modeling.
Instructions
Calculate gas pseudopressure difference (m(p)).
CRITICAL GAS ANALYSIS TOOL - Computes pseudopressure difference, a pressure transformation that linearizes the gas diffusivity equation. This makes gas flow analysis mathematically similar to liquid flow, enabling use of liquid flow solutions for gas systems. Essential for accurate gas well performance analysis.
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.
p1 (float, required): Initial pressure in psia. Must be > 0. Typically reservoir pressure. Example: 1000.0.
p2 (float, required): Final pressure in psia. Must be > 0. Typically sandface pressure. Example: 3500.0.
h2s (float, optional, default=0.0): H2S mole fraction (0-1). Typical: 0-0.05. Example: 0.0.
co2 (float, optional, default=0.0): CO2 mole fraction (0-1). Typical: 0-0.20. Example: 0.0.
n2 (float, optional, default=0.0): N2 mole fraction (0-1). Typical: 0-0.10. Example: 0.0.
zmethod (str, optional, default="DAK"): Z-factor method for integration. Options: "DAK", "HY", "WYW", "BUR". DAK recommended.
Pseudopressure Formula: m(p) = 2∫(p/(μZ))dp from p1 to p2
Where:
p = pressure (psia)
μ = gas viscosity (cP)
Z = gas compressibility factor
Why Pseudopressure: Gas properties (Z, μ) vary significantly with pressure, making gas flow non-linear. Pseudopressure transformation accounts for these variations, enabling:
Use of liquid flow solutions for gas
Linear pressure analysis
Accurate well test interpretation
Material balance calculations
Applications:
Gas Well Testing: Pressure transient analysis, rate transient analysis
Material Balance: P/Z vs cumulative production plots
Reservoir Simulation: Input for gas flow calculations
IPR Curves: Inflow performance relationship generation
Returns: Dictionary with:
value (float): Pseudopressure difference in psia²/cP
method (str): Integration method with Z-factor method used
units (str): "psia²/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 pseudopressure with actual pressure
Using wrong pressure order (p1 should be lower than p2 typically)
Temperature in Celsius instead of Fahrenheit
Example Usage:
{
"sg": 0.7,
"degf": 180.0,
"p1": 1000.0,
"p2": 3500.0,
"h2s": 0.0,
"co2": 0.0,
"n2": 0.0,
"zmethod": "DAK"
}Result: Pseudopressure difference ≈ 1-5 × 10⁶ psia²/cP (typical range).
Note: Pseudopressure is essential for accurate gas flow calculations. Always use reservoir conditions. Account for all non-hydrocarbon components. The integration is performed numerically, so results are approximate but highly accurate.
Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| request | Yes |
Output Schema
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||