Make simple grid
Make a grid without faults
The Make simple grid process, which is located under Utilities, makes it easy to create a grid without faults. The geometry of the grid is defined by the input to the process.
A project boundary can be added, or minimum and maximum values from x, y, and z can be used.
Make simple grid
Result
Skeleton
A top, mid, and base skeleton grid is generated. Further subdivision in the vertical direction is needed.
If the process is run without using surfaces to define horizons, the result is a skeleton grid.
A “skeleton grid” is a Petrel term for the framework that is made as the first step towards defining a 3D grid. A skeleton grid consists of a top, mid, and bottom mesh defined by pillars. The pillars define the lateral position of the corners in the three meshes, and the z-position is defined as the bottom, mid point, and the top of the pillars. After the skeleton grid is generated, it needs to be further subdivided in the vertical direction. This is done by inserting surfaces. The topmost and the bottommost surface that are inserted define the top and the bottom of the final 3D grid, hence, the top and the bottom skeleton grid are usually outside the final 3D grid.
The reason why 3D grids are generated this way in Petrel is that the gridding process starts with modeling the faults, which are defined using pillars. Those pillars are then used to define the geometry of the 3D grid. The processes used to make grids based on fault modeling are
Make simple grid
With Insert Horizons
Skeleton with horizons
If you have surfaces that describe the horizons, you can enter them as input.
If you have surface data in the Input pane that describes the horizons, you can drop them into the Input data tab of the Make simple grid process. The result will be a skeleton grid with horizons.
Make simple grid
Vertical subdivision
Make Horizons
Insert a horizon in the grid to define different zones.
Layering
Further subdivision is done by employing the Layering process.
Vertical subdivision
The Make horizons, Make zones, and Layering processes are used to perform further vertical subdivision.
Make Horizons - This process usually defines the main depositional
units of the 3D grid and are, in most cases, the layers identified and interpreted on seismic data. The Make horizons process samples input surfaces into the 3D Grid. Note that a “Horizon” in Petrel is a surface that is a part of the 3D grid.
Make zones – This process defines the sub-units of the 3D grid. The
process inserts additional horizons (and zones) into the 3D grid by inserting isochores up or down from the previously input horizons. The isochores can be gridded thickness maps or calculated directly from well tops. Zones can also be defined as specific thickness intervals or percentages of the main zone.
Layering – The final step is to make the final vertical resolution of the
3D grid.
To keep the modeling simple, we will not perform the Make zones process. That is, we assume that the stratigraphic layering is defined by the surfaces that we insert. Then we will do layering to obtain a suitable resolution for simulation.
Make Horizons
1. Append desired number of horizons in the table. 2. Drop in interpretations or surfaces using the blue arrow.
The Make Horizons process
Double-click on the Make horizons process to open its process dialog and select the Horizon tab. In the table that appears, insert the number of horizons to be generated.
The Multiple drop option allows you to insert a list of items in one go into the Input#1 column: Make sure your input horizons are sorted in the correct stratigraphic order in the Input pane, then select the first item, and click on the first blue arrow under Input#1. All of the input horizons will then be inserted in the same order as they appear in the
Input pane. Horizon names are updated according to input names, but
can be overwritten if desired.
Horizon Type:
You should specify whether the horizon is an Erosional, General, Discontinuous or a Base surface.
• Erosional surfaces will erode surfaces below
• Surfaces above a Base surface will be on lapped to the Base. • Surfaces above a Discontinuous surface will be on lapped on it
and surfaces below will be truncated by it.
Make horizons
Result
The horizons appear in the Models pane. Select the check box to view in a 3D window.
Available for displaying:
1. Edges - to see
zone division
2. Zone filter - to
view selected layers
Make Horizons – Output
Horizons folder – The layers added in the Make horizons and Make zones process will be stored in the Horizons folder.
Fault filter – The fault filter will allow you to visualize the fault throw
for just one horizon at a time and is mainly used for mapping purposes.
Zone filter – A zone in Petrel is defined as the thickness between two
horizons, and is created in either Make horizon or in the Make zones process. The zone filter allows you to visualize the edges and the I- and J- intersections of the 3D grid zone by zone. The zone filter is also applicable for properties when we generate these in the 3D grid.
Layering
1. Specify the Zone division.
2. Specify number of layers (Proportional), cell
thickness (Follow top/Base) or Fractions. Proportional Follow Base Follow Top
Fractions
Follow Base with Reference
The Layering process
After the Make horizons (and the Make zones) process is run, further layering is inserted by running the Layering process. You can select four different ways of doing the layering:
• Proportional: The zone will be divided into Number of
layers, equally thick layers
• Follow base: The zone will be divided into layers with thickness Cell thickness, starting to build from the horizon below.
• Follow top: The zone will be divided into layers with thickness
Cell thickness, starting to build from the horizon above.
• Fractions: The zone will be divided into a number of layers with relative thickness as given in the input. Example: If the input is 1, 2, 2, the zone is divided into three layers where the two last layers are twice as thick as the first one.
The illustration above shows three different ways of specifying the layering; Follow base, Fractions and Proportional.
Note that the zone division should reflect the horizon type. If, for instance, a horizon is of type Base, the zone above should be of type
Follow base, Proportional, or Fractions.
Proportional and Fractions give the least “pinched out” layers and
Model a fault
Digitizing
Employ the Make/edit polygons process to digitize a line that defines the fault plane.
The new polygon appears at the bottom of the Input pane.
A simulation fault can be inserted into the simple grid at the position of existing grid nodes. To approximately give the geometry of the new fault, you can draw a polygon within the simple grid.
The Make/edit polygons process is placed under Utilities on the
Processes pane. When the process is active, tools for digitizing
polygons appear in the function bar at the right of the display window. Use the process to digitize a line that defines the geometry of the fault. The new polygon is stored at the bottom of the Input pane.
Model a fault
Convert to fault
The polygon can be converted into a fault in the active grid
To insert the fault into the grid, make sure that the grid is selected in the Models pane. Then right-click the polygon you just made, and select Convert to fault. The polygon is then converted into a fault in the active grid. The new fault is stored on the Faults sub-folder of the 3D grid.
Model a fault
Define transmissibility
Use the Fault analysis process to assign transmissibility to the fault
You need to assign a transmissibility multiplier to the fault in order to use it in a simulation. The transmissibility multiplier defines to which degree the fault is a barrier to flow. A multiplier of zero means that no flow goes through the fault.
To assign a transmissibility multiplier to a fault, make sure that the fault is active, then open the Fault analysis process. In the dialog that opens, select to assign a constant multiplier, or to define a multiplier based on standard equations. A new property is created and stored under the Fault properties folder in the Models pane. Details of how to define the transmissibility multiplier will be provided later in the course.
Exercises - Making a simple grid a with
simulation fault
In this exercise, you will make a simple simulation model of a two- phase black oil case. You will start by defining a simple grid with a vertical fault. You will then go through all of the steps required until you have a model ready for running a simulation. And finally, you will run the simulation and view the results.
Exercise Workflow
• Make a simple grid • Insert a simulation fault
Exercise Data
In this exercise, we use the Start_2010.pet.
Making a simple grid
Exercise steps
1. Open the Start_2010.pet project.
2. Open the Make simple grid process located under Utilities in the Processes pane.
3. Select a name for the new grid, for example Simple. 4. On the Input data tab, select the Insert surface option. 5. Drop in the surfaces Top reservoir, Mid, and Base from the
Surfaces folder on the Input pane by clicking the Append
6. Drop in the Project boundary from the Input pane into the
Boundary field by clicking the blue arrow.
7. Select the Geometry tab, and click the Get limits from
selected button. As the project boundary is selected on the Input pane, Petrel will use that as a boundary for the grid.
8. Select a Grid increment of 350 m in both the X and Y direction. Click OK.
9. Your new grid is stored in the Models pane. Select to view the skeleton grid in a 3D window.
10. We will now define the vertical sub-division of the 3D grid. Open the Layering process under Corner point gridding. Divide ‘Zone 1’ into 7 layers and ‘Zone 2’ into 3 layers. Press
OK. Select to view ‘Edges’ under the 3D grid in the Models
pane to see the result of the layering.
Making a simulation fault
In this exercise, you will add a “Simulation fault” to the model. If you want to add a fault with throw, you need to use a more advanced gridding processes in Petrel. That is, you will have to use the Fault
modeling and the Pillar gridding process. Exercise steps
1. Open a 3D window and select to view both the Top reservoir horizon and the faults from the Fine grid.
2. Observe that the faults have a throw. For example, across
Fault5 the throw is so large that there is no communication
across. We will now insert a simulation fault in the simple grid to model this behavior.
3. Open a new 2D window and display the Base horizon from the Simple grid and the Project boundary from the Input pane along with Fault5 from the Fine grid.
4. If you cannot see the fault, open the Settings of the Faults folder of the Fine grid, and make sure the option Show
5. Digitize a line that will be used to define the fault plane by first selecting the Make/edit polygons process in the Utilities folder in the Processes pane. Then:
a. Activate the Make/edit polygons tool in the function bar. Select the Add new points tool .
b. Digitize a line that follows Fault5 by pointing in the display and left-clicking. Add a point in the grid cell closest to the project boundary to make sure the fault is extended all the way to the boundary.
6. The polygon is stored at the bottom of the Input pane. Rename it to “Fault polygon” by opening the Settings for it and changing the name in the Info tab.
7. Make sure the Simple grid is selected on the Models pane. 8. Right-click on the polygon you just made, and select Create
simulation (grid) fault from the drop-down menu. The new
fault is stored in the Faults folder under the simple grid on the
Models pane.
Exercise steps
1. Open a 3D window and select to view your new fault. 2. Open the Fault analysis process that is located in the
Property modeling folder.
3. Enter a constant transmissibility multiplier of 0 (sealing fault) Click OK.
Summary
The basics of the Petrel user interface were presented in this module. In particular, how to open and use windows and how to access and alter the settings of objects. Also introduced were the eight different panes in Petrel which store and provide access to data, processes, windows, workflows and simulation results. In addition, how to make a simple simulation grid with layering based on surface information was presented along with how to add a fault to such a grid and how to assign properties to the fault.