Two-Phase ViewGen calculations

Checking the input data

ViewGen reads all the two-phase fault rock data specified in WizGen. Two-phase plugins (if used) are checked for consistency at the same time as the single-phase ones. Note that even if equations are used for all two-phase properties, the system represents these relationships as plugins. If a plugin contain errors, ViewGen will terminate with an error message. This kind of error will only arise if user-defined plugins have not been checked (by clicking on the BUILD option on the User-defined plugins page of WizGen) and any errors eliminated prior to using ViewGen.

Defining the cell groups

Groups are created at the end of a ViewGen run, according to the divisions and priorities assigned as Two phase flow - Groupings settings in WizGen.     

Each cell in the model is inspected for faulted faces. A series of calculations is performed to determine if a faulted face is in the drainage or imbibition cycle and to evaluate the fault thickness and permeability, flow rate through the fault and the length, permeability and porosity of the cell containing the face. These data, combined with the SATNUM of the cell, are stored as groups.

Information about the groups is output by ViewGen to a temporary file (groupings.out) stored in the project  _OUTPUT  directory. This file is used by the 2PhaseGen module.

A group is defined by the following items:-
FAULT CYCLE (Drainage or Imbibition)
CELL SATNUM (i.e. original cell relative permeability and capillary pressure functions)
FAULT PERMEABILITY (calculated from single-phase TransGen definitions)
FAULT THICKNESS (calculated from single-phase TransGen definitions)
FLOW RATE (imported directly or calculated from cell pressures)
CELL PERMEABILITY (imported)
CELL POROSITY (imported)
CELL LENGTH (calculated from the model geometry)

An example of a temporary groupings.out file is given below. The contents of the file are shown for completeness only; the user should not have to interact with this file:

BeginParameters
     FaultFlowRate: 2 2 6
     FaultPermeability: 2 2 2
     FaultThickness: 2 2 4
     CellPermeability: 2 2 3
     CellPorosity: 2 3 5
     CellLength: 2 2 1
EndParameters
# Definition of group number 7
BeginGroup
    GroupNumber: 7
    FaultCycle: DRAINAGE
    RelPermTableIdx: 1
    FaultFlowRate: 0.000706286 0
    CellPorosity: 0.080282 0
    FaultThickness: 0.203895 0
    CellPermeability: 213.029 0
    FaultPermeability: 0.00334088 0
    CellLength: 75.1753 0
EndGroup
# Definition of group number 8
BeginGroup
    GroupNumber: 8
...
etc
EndGroup

The parameters at the top of the file report number of divisions in the drainage cycle, the number of divisions in the imbibition cycle, and the parameter priority, for the 6 grouping variables, as input in WizGen (via the Two phase flow - GROUPINGS & OUTPUT page). This is followed by a listing of the values or settings for each group in the model. In this example the original model contained 6 SWOF tables, hence the first group defined for up-scaling is number 7.

Exporting the KRNUM tables

Once each faulted cell face has been assigned to a group, this information is output using the directional KRNUM keywords to the file specified in the  Two-Phase flow - Output section of WizGen. For unfaulted cell faces and for all cells in the two vertical directions (i.e. KRNUMZ and KRNUMZ-), the original SATNUM index of the cell is used. (See example of KRNUM output file).

Displaying Two-Phase fault rock properties

At present the following can be displayed in ViewGen:-

The 6 KRNUM keywords can be visualised as cell properties.

Cell pressures (if used) can be visualised as cell properties.

Across- fault flow rates (if used explicitly) can be visualised as fault properties.

No internally-derived properties (e.g. fault-rock capillary threshold pressure, porosity, connate water saturation, effective water saturation range, etc.) can be visualised directly. However, these properties can be displayed via a workaround using the single-phase plugins and user-defined cell properties.