The properties package

The fmu.tools properties package provides functionality (methods) to special calculations in e.g. RMS. Currently a library for computing water saturation is present.

Generic water saturation calculations

Water saturation in RMS user interface is limited to Leverett J functions and lookup functions. However there is a need to extend this to Leverett J function which has an additional constant term, and to BVW and Brooks-Corey methods. The function offers several options:

• Using direct methods (cell mid-point) or integrate across cell thickness

• Look at the center line (vertically) through cells, og use cells corners.

• Both normal and inverse formulation of Leverett J is supported.

• Normalization is supported.

The theory is given in the PDF file provided here: pdf.

Note that this library will not give exact same values as RMS built-in Sw GUI will give. This is partly due to computing height across a cell is a bit different implemented.

The library input is documented here: SwFunction()

Example: Using simple Sw Leverett J

The Leverett J is given as $S_w = a J^b$, where $J$ is $hsqrt(k/phi)$. In this example, the factors are constant numbers:

import numpy as np
import xtgeo
from fmu.tools.properties import SwFunction

GRIDNAME = "Geogrid"
A = 1
B = -2
FWL = 1700

PORONAME = "PHIT"
PERMNAME = "KLOGH"

CALC = "integrated"
METHOD = "cell_corners_above_ffl"

SW_RESULT = "SwJ"


def compute_saturation():
    grid = xtgeo.grid_from_roxar(project, GRIDNAME)
    poro = xtgeo.gridproperty_from_roxar(project, GRIDNAME, PORONAME)
    perm = xtgeo.gridproperty_from_roxar(project, GRIDNAME, PERMNAME)

    # avoid zero porosities in the division below
    poro.values[poro.values == 0.0] = 0.01
    x = poro.copy()
    x.values = np.sqrt(np.divide(perm.values, poro.values))

    sw_func = SwFunction(
        grid=grid,
        x=x,
        a=A,
        b=B,
        ffl=FWL,
        invert=True,
        method=METHOD,
    )
    sw = sw_func.compute(CALC)
    sw.values[poro.values < 0.05] = 1.0  # 100% water when low porosity
    sw.to_roxar(project, GRIDNAME, SW_RESULT)


if __name__ == "__main__":
    compute_saturation()
    print("Done")