co2_brine_mutual_solubility

Calculate CO2-brine mutual solubilities and properties.

CRITICAL CO2-BRINE SYSTEM TOOL - Computes comprehensive properties for CO2-saturated brine systems using the Duan & Sun (2003) model. Essential for CO2 sequestration, CO2-EOR, and geothermal applications. Accounts for mutual solubility (CO2 in brine, H2O in CO2-rich phase).

Parameters:

• pres (float, required): Pressure in psia (field) or bar (metric). Must be > 0. Typical: 1000-5000 psia. Example: 3000.0 psia.

• temp (float, required): Temperature in °F (field) or °C (metric). Typical: 100-400°F. Example: 180.0°F.

• ppm (float, required): Salinity in parts per million (ppm) NaCl. Typical: 0-200000 ppm. Example: 50000 ppm (5 wt%).

• metric (bool, optional, default=False): Unit system flag. False = field units (psia, °F), True = metric (bar, °C).

• cw_sat (bool, optional, default=True): Compressibility calculation flag. True = saturated compressibility, False = undersaturated.

Properties Calculated:

• Phase Equilibrium:

  • Aqueous phase mole fractions (x_CO2, x_H2O)

  • Vapor phase mole fractions (y_CO2, y_H2O)

  • Salt mole fraction

• Densities:

  • CO2-rich gas density (gm/cm³)

  • Brine CO2-saturated density (gm/cm³)

  • Brine pure density (gm/cm³)

  • Fresh water density (gm/cm³)

• Viscosities:

  • Brine CO2-saturated viscosity (cP)

  • Brine pure viscosity (cP)

  • Fresh water viscosity (cP)

• Formation Volume Factors:

  • Bw CO2-saturated (rb/stb)

  • Bw pure (rb/stb)

  • Bw fresh (rb/stb)

• Compressibility:

  • Undersaturated compressibility (1/psi or 1/bar)

  • Saturated compressibility (1/psi or 1/bar)

• Solution GOR: CO2 dissolved in brine (scf/stb or m³/m³)

Mutual Solubility: CO2-brine systems exhibit mutual solubility:

• CO2 dissolves in brine (increases with pressure, decreases with salinity)

• H2O dissolves in CO2-rich phase (increases with temperature)

• Both solubilities depend on pressure, temperature, and salinity

Physics: Uses Duan & Sun (2003) model for CO2-H2O-NaCl systems accounting for:

• Pressure effects on solubility (higher P = more CO2 dissolved)

• Temperature effects (higher T = less CO2 dissolved, more H2O in vapor)

• Salinity effects (higher salinity = less CO2 dissolved)

• Mutual solubility (both phases contain both components)

Applications:

• CO2 Sequestration: CCS project design, storage capacity evaluation

• CO2-EOR: Enhanced oil recovery with CO2 injection, miscibility studies

• Geothermal: CO2-based geothermal systems, supercritical CO2

• Aquifer Storage: Underground CO2 storage capacity, leakage assessment

• Material Balance: CO2-brine material balance calculations

Salinity Conversion:

• 1 wt% = 10,000 ppm

• Seawater ≈ 35,000 ppm (3.5 wt%)

• Formation brine: 50,000-200,000 ppm (5-20 wt%)

Returns: Dictionary with:

• phase_equilibrium (dict): Mole fractions in aqueous and vapor phases

• densities (dict): All density values (CO2-rich, saturated, pure, fresh)

• viscosities (dict): All viscosity values (saturated, pure, fresh)

• formation_volume_factors (dict): Bw values (saturated, pure, fresh)

• compressibility (dict): Undersaturated and saturated compressibility

• solution_gor_co2 (float): CO2 dissolved in brine

• viscosibility_per_bar_or_psi (float): Viscosibility coefficient

• method (str): "Duan & Sun (2003) CO2-H2O-NaCl model"

• units (str): "metric" or "field"

• note (str): Usage guidance

• inputs (dict): Echo of input parameters

Common Mistakes:

• Using wrong unit system (check metric flag)

• Salinity in wt% instead of ppm (must convert: ppm = wt% × 10000)

• Pressure in barg/psig instead of psia (must be absolute)

• Temperature in wrong units (check metric flag)

• Not accounting for mutual solubility (both phases contain both components)

• Using wrong compressibility (saturated vs undersaturated)

Example Usage (Field Units):

{
    "pres": 3000.0,
    "temp": 180.0,
    "ppm": 50000,
    "metric": False,
    "cw_sat": True
}

Result: CO2 solubility in brine ≈ 20-40 scf/stb, H2O in CO2-rich phase ≈ 0.1-1 mol%.

Note: CO2-brine mutual solubility is critical for CCS and CO2-EOR projects. Always use correct unit system (field vs metric). The model accounts for mutual solubility which is significant at high pressures and temperatures. Salinity significantly reduces CO2 solubility - use correct formation water salinity.