Table of Contents
Many problems will be run in two stages: (1) an analysis that establishes a steady state initial condition, and (2) an analysis that loads the steady state results as an initial condition and then proceeds with a transient disturbance, such as a spill or production from a reservoir. PetraSim makes it easy to load the results of a previous analysis as the starting condition of a new analysis.
The PetraSim interface helps guide the user through the steps of an analysis. These include:
Selecting an EOS.
Defining the problem boundaries and creating a mesh.
Selecting the global options to be used in the analysis.
Specifying the material properties.
Defining the default initial conditions for the model, either directly or by loading the results of a previous analysis.
Using the grid editor to define cell-specific data, such as material, sources, sinks, and initial conditions.
Setting the solution and output options.
Solving the problem.
Post-processing of results using contour and time history plots.
The user must recognize that this process is seldom linear. It will likely be necessary iterate as new understanding of the model and physics is obtained. New users are especially tempted to immediately proceed with a complex model. Don't do this! It is always recommended that the user perform a 1D and 2D analyses before a 3D analysis.
A suite of examples taken from the TOUGH user guides is available at http://www.petrasim.com/.
PetraSim uses multiple views to display the model and results:
3D View. Used to rapidly view the model, including internal boundaries and wells.
Tree View. Used to display and select regions in the model, materials, wells, and extra cells.
Grid Editor. Used to define cell-specific parameters including sources and sinks and initial conditions.
3D Plots. Used to display isosurfaces and contour plots of results.
Time History Plots. Used to display detailed cell results as a function of time.
To navigate using the 3D model:
To spin the 3D model left-click on the model and move the mouse. The model will spin as though you have selected a point on a sphere.
To zoom, hold the Alt key and drag the mouse vertically.
To move the model, hold the Shift key and drag to reposition the model in the window.
To reset the model, type "r" or select
.To change to a standard view, select
for a top view, 
for a front view, and 
for a side view.
The Grid Editor is used to make cell-specific changes to the model. Select Model->Edit Grid or 
to open the grid editor.
The Grid Editor will display a section through the model, Figure 5.1. To change the properties of a cell, either select the cell and then Edit->Properties or right-click on the cell.
In the toolbar, you can select the viewing direction, the grid layer, and the property to be plotted. Tools include selection 
, zoom in 
, zoom out 
, zoom box 
, drag 
, previous view 
, next view 
, and reset 
.
To help with orientation in the model, the layer being viewed in the Grid Editor is highlighted in the 3D View, Figure 5.2.
The Tree View (on the left of the 3D window) is used to display and select regions, materials, wells, and extra cells. Expand the list and then double-click on an object to edit its properties.
In the Grid Editor, the Properties of a cell can be set to Type Enabled, Disabled, or Fixed State, with the following meanings:
An Enabled cell is a standard cell in the analysis.
A Disabled cell will not be included in the analysis. No information about this cell will be written to the TOUGH input file. It will not be included in the results.
An Fixed State cell is used to set boundary conditions. The cell is included in the analysis, but the state of the cell (Pressure, Temperature, etc.) will not change. In the TOUGH2 User's Guide, such cells are named "Inactive". It was necessary for us to use a different name to distinquish between Fixed and Disabled cells.
All input uses standard metric (SI) units, such as meters, seconds, kilograms, degrees C, and the corresponding derived units, such as Newton, Joules, and Pascal for pressure.
Externally generated contour data can be used to define 3D inital conditions or to define the topology of the top and bottom of the model. This data is read from a contour file.
The format of the contour file is given below; it follows that used by TETRAD. The contour data can be viewed as a set of planes on which contours are defined. The planes can be defined at several depths in the model, forming a complete 3D definition of the data. Linear interpolation is performed in the Z direction between the contour planes.
The data consists of the depth (Z coordinate) followed by a definition of contours at that depth. In the following example, the "!" and following comments are included only for description. These should not be included in an actual file.
Define top of reservoir ! The first line is a description
<top origin> ! Include this line (not used at this time)
<depth> ! Keword to indicate beginning of a contour set
0. ! The Z coordinate for this contour set
<contour> ! Keyword to define a contour at the given depth
0. 1 ! Value of contour followed by number of points
-1000. 1000. ! X and Y coordinates of the point(s)
<contour> ! Start of a new contour
200. 3 ! Value (200.0) and number of points (3)
-100. 1000. ! X and Y coordinates of the point(s)
-300. 800. ! X and Y coordinates of the point(s)
-1000. 200. ! X and Y coordinates of the point(s)
<contour> !
100. 4 ! Complete the contours at this depth.
200. 1000.
0. 600.
-400. 200.
-800. 0.
<contour>
0. 4
400. 1000.
200. 600.
-200. 200.
-600. 0.
<contour>
0. 2
1000. 0.
1000. 1000.
! Repeat <depth> and <contour> data