Import reservoir simulator results

Both static and dynamic reservoir simulator results are used in the pem. They are complemented with some results from the geomodel, as described below. Capital letter names below refer to the parameter names in eclipse models, which is the main reservoir simulator tool within Equinor. OPM FLOW is an alternative, and it is compatible with eclipse parameter names.

Directory and file names for result files

The directory name for the result files from the reservoir simulator is fixed within the FMU directory structure. The file names are also fixed, but they are links/pointers to the actual results from eclipse. The directory and file names used by pem are shown below:

rel_path_simgrid: ../../sim2seis/input/pem

> cd ../../sim2seis/input/pem
> ls -l ECLIPSE*
lrwxrwxrwx 1 hfle fmu        36 Jun 26  2024 ECLIPSE.EGRID -> ../../../eclipse/model/ECLIPSE.EGRID
lrwxrwxrwx 1 hfle fmu        35 Jun 26  2024 ECLIPSE.INIT -> ../../../eclipse/model/ECLIPSE.INIT
lrwxrwxrwx 1 hfle fmu        36 Jun 26  2024 ECLIPSE.UNRST -> ../../../eclipse/model/ECLIPSE.UNRST
>

Static results

There are only two static results from the reservoir simulator model which are used in pem: PORO and DEPTH. Earlier, NTG was also used, but we now advise using volume fractions from the geomodel. Static results are found in the .INIT file of the reservoir simulator.

Volume fraction files

As mentioned above, pem is not based on using the NTG parameter from the reservoir simulator, as it is often a binary parameter, and does not reflect variations in shale fraction in the Geomodel. Additionally, to capture variations in effective mineral properties, more volume fractions may be required, such as coal or calcite in a clastic case, and calcite, dolomite, mud etc. in a carbonate case. Volume fractions should be exported from the Geomodel with the same grid resolution as the reservoir simulator grid, and in the .roff format.

  volume_fractions:
    rel_path_fractions: ../../sim2seis/input/pem
    fractions_prop_file_names: [simgrid--vsh_pem.roff, ]
    fractions_are_mineral_fraction: False  # volume fractions, not mineral fractions are assumed by default
  fraction_names: [vsh_pem, ]  # matching the names of properties in the fractions properties file
  fraction_minerals: [shale, ] # each of the minerals must be defined with bulk modulus, shear modulus and density
  shale_fractions: [vsh_pem, ] # define the non-reservoir fraction(s)
  complement: quartz  # if not all fractions add up to 1.0

Volume fractions to mineral fractions

It is important to know the definition of volume fractions. The standard definition in petrophysics is that volume fractions and effective porosity comprise the bulk volume. This definition is the default value in pem.

In a case where only VSH is defined, and we wish to calculate VSST, we do it simply by:

$$VSST=1.0-VSH-POR$$

However, when effective mineral properties are calculated, the volume fractions must be transformed into mineral fractions, i.e. fractions of the rock matrix:

$$FRA{C}_{S}ST=VSST/(1.0-POR);FRA{C}_{S}H=VSH/(1.0-POR)$$

NB! It is possible to override the volume fraction assumption by ticking on the option for fractions_are_mineral_fraction in the parameter interface or setting it to true in the YAML file. In that case the fraction of sandstone in the example above becomes:

$$FRA{C}_{S}ST=1.0-FRA{C}_{S}H$$

Dynamic results

Dynamic results for each time step in the .UNRST file are used to calculate fluid properties and other properties that depend on pressure.

# TEMP will only be available for eclipse-300
RST_PROPS = ["SWAT", "SGAS", "SOIL", "RS", "RV", "PRESSURE", "SALT", "TEMP"]

Salinity may not be available in the UNRST file, and in that case, a constant value must be set in the YAML file. Temperature in normally also kept constant. RS (ratio of solid) and RV (ratio of vapour) are used for calculating oil properties and condensate properties, respectively. If both are present in the UNRST file, it may be necessary to state if the fluid model should include condensate calculation. Beware that condensate model is not part of the open-source foundation for pem; a proprietary model is needed.

  calculate_condensate: False