pyResToolbox MCP Server

Calculate oil viscosity (μo).

CRITICAL PVT PROPERTY - Computes oil viscosity at reservoir conditions. Viscosity affects flow rates, pressure drops, and recovery efficiency. Uses Beggs-Robinson (1975) correlation, industry standard for oil viscosity.

Parameters:

• api (float, required): Oil API gravity in degrees. Valid: 0-100. Example: 35.0. Higher API = lighter oil = lower viscosity.

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

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

• pb (float, optional, default=0.0): Bubble point pressure in psia. Required for accurate calculation. Example: 3500.0.

• 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.

• method (str, optional, default="BR"): Correlation method. Only "BR" available.

Viscosity Behavior:

• p < pb: Viscosity decreases with pressure (more gas dissolves, oil thins)

• p = pb: Viscosity reaches minimum (μob, typically 0.5-5 cP)

• p > pb: Viscosity increases with pressure (oil compression)

Typical Ranges:

• Light oils (API > 35): 0.5-2 cP at bubble point

• Medium oils (API 25-35): 1-10 cP at bubble point

• Heavy oils (API < 25): 10-1000+ cP at bubble point

Returns: Dictionary with:

• value (float or list): Viscosity in cP (matches input p shape)

• method (str): "BR" (Beggs-Robinson)

• units (str): "cP"

• inputs (dict): Echo of input parameters

Common Mistakes:

• Not providing rs when p < pb (will calculate incorrectly)

• Using dead oil viscosity instead of live oil viscosity

• Temperature in Celsius instead of Fahrenheit

• Pressure in barg/psig instead of psia

Example Usage:

Result: Viscosity decreases from ~1.2 cP at 2000 psia to ~0.8 cP at 3500 psia, then increases to ~0.85 cP at 4000 psia (above bubble point).

Note: Viscosity is highly sensitive to temperature and dissolved gas content. Always use reservoir temperature, not separator temperature.