pyResToolbox MCP Server

Instructions

{
    "sg": 0.7,
    "degf": 180.0,
    "p": [1000, 2000, 3000, 4000],
    "h2s": 0.0,
    "co2": 0.05,
    "n2": 0.01,
    "zmethod": "DAK"
}

Implementation Reference

• src/pyrestoolbox_mcp/tools/gas_tools.py:313-403 (handler)

  The gas_viscosity tool handler function. Calculates gas viscosity using pyrestoolbox.gas.gas_ug with Lee-Gonzalez-Eakin correlation. Handles scalar and array inputs, converts numpy arrays to lists for JSON, and returns structured response.

  @mcp.tool()
  def gas_viscosity(request: GasViscosityRequest) -> dict:
      """Calculate gas viscosity (μg).
  
      **CRITICAL GAS PVT PROPERTY** - Computes gas viscosity at reservoir conditions
      using Lee, Gonzalez & Eakin (1966) correlation, industry standard for natural gas.
      Viscosity affects flow rates, pressure drops, and well performance. Gas viscosity
      increases with pressure and temperature, opposite to liquid behavior.
  
      **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.
      - **p** (float or list, required): Pressure(s) in psia. Must be > 0.
        Can be scalar or array. Example: 3500.0 or [1000, 2000, 3000, 4000].
      - **h2s** (float, optional, default=0.0): H2S mole fraction (0-1).
        Typical: 0-0.05. Example: 0.02.
      - **co2** (float, optional, default=0.0): CO2 mole fraction (0-1).
        Typical: 0-0.20. Example: 0.05.
      - **n2** (float, optional, default=0.0): N2 mole fraction (0-1).
        Typical: 0-0.10. Example: 0.01.
      - **zmethod** (str, optional, default="DAK"): Z-factor method for viscosity calculation.
        Options: "DAK", "HY", "WYW", "BUR". DAK recommended.
  
      **Viscosity Behavior:**
      - Increases with pressure (gas molecules closer together)
      - Increases with temperature (molecular motion increases)
      - Typical range: 0.01-0.05 cP at reservoir conditions
      - At standard conditions: ~0.01 cP
  
      **Lee-Gonzalez-Eakin Correlation:**
      Uses Z-factor internally to account for real gas behavior. More accurate than
      ideal gas assumptions, especially at high pressures.
  
      **Returns:**
      Dictionary with:
      - **value** (float or list): Viscosity in cP (matches input p shape)
      - **method** (str): "Lee-Gonzalez-Eakin"
      - **units** (str): "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 gas viscosity (increases with P) with oil viscosity (decreases with P)
      - Temperature in Celsius instead of Fahrenheit
  
      **Example Usage:**
      ```python
      {
          "sg": 0.7,
          "degf": 180.0,
          "p": [1000, 2000, 3000, 4000],
          "h2s": 0.0,
          "co2": 0.05,
          "n2": 0.01,
          "zmethod": "DAK"
      }
      ```
      Result: Viscosity increases from ~0.012 cP at 1000 psia to ~0.025 cP at 4000 psia.
  
      **Note:** Gas viscosity is much lower than oil viscosity (typically 0.01-0.05 cP
      vs 0.5-10 cP). Always use reservoir conditions, not separator conditions.
      Account for all non-hydrocarbon components for accuracy.
      """
      method_enum = getattr(z_method, request.zmethod)
  
      ug = gas.gas_ug(
          sg=request.sg,
          degf=request.degf,
          p=request.p,
          h2s=request.h2s,
          co2=request.co2,
          n2=request.n2,
          zmethod=method_enum,
      )
  
      # Convert numpy array to list for JSON serialization
      if isinstance(ug, np.ndarray):
          value = ug.tolist()
      else:
          value = float(ug)
  
      return {
          "value": value,
          "method": "Lee-Gonzalez-Eakin",
          "units": "cP",
          "inputs": request.model_dump(),
      }

• src/pyrestoolbox_mcp/models/gas_models.py:103-139 (schema)

  Pydantic model defining the input schema for gas_viscosity tool, including validation for fields like sg, degf, p (scalar or list), non-hydrocarbon fractions, and zmethod.

  class GasViscosityRequest(BaseModel):
      """Request model for gas viscosity calculation."""
  
      sg: float = Field(
          ..., ge=0.5, le=2.0, description="Gas specific gravity (air=1, dimensionless)"
      )
      degf: float = Field(
          ..., gt=-460, lt=1000, description="Temperature (degrees Fahrenheit)"
      )
      p: Union[float, List[float]] = Field(
          ..., description="Pressure (psia) - scalar or array"
      )
      h2s: float = Field(
          0.0, ge=0.0, le=1.0, description="H2S mole fraction (dimensionless)"
      )
      co2: float = Field(
          0.0, ge=0.0, le=1.0, description="CO2 mole fraction (dimensionless)"
      )
      n2: float = Field(
          0.0, ge=0.0, le=1.0, description="N2 mole fraction (dimensionless)"
      )
      zmethod: Literal["DAK", "HY", "WYW", "BUR"] = Field(
          "DAK", description="Z-factor calculation method"
      )
  
      @field_validator("p")
      @classmethod
      def validate_pressure(cls, v):
          """Validate pressure values."""
          if isinstance(v, list):
              if not all(p > 0 for p in v):
                  raise ValueError("All pressure values must be positive")
          else:
              if v <= 0:
                  raise ValueError("Pressure must be positive")
          return v

• src/pyrestoolbox_mcp/server.py:17-25 (registration)

  Imports and calls register_gas_tools(mcp), which defines and registers the gas_viscosity tool (among others) using @mcp.tool() decorator.

  from .tools.gas_tools import register_gas_tools
  from .tools.inflow_tools import register_inflow_tools
  from .tools.simtools_tools import register_simtools_tools
  from .tools.brine_tools import register_brine_tools
  from .tools.layer_tools import register_layer_tools
  from .tools.library_tools import register_library_tools
  
  register_oil_tools(mcp)
  register_gas_tools(mcp)