1. science
2. geology
3. seismology
4. earthquakes

Geophysicist El-Sayed Fathi Mubarak
Petrel Software Work Flow
By
Geophysicist
El-Sayed Fathy Moubark
Part 2
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Geophysicist El-Sayed Fathi Mubarak
Fault Modeling
The purpose of this process is to build a fault model using
variety of fault data. There are several ways of defining the fault
model in Petrel. A fault model can be generated based on fault
polygons, interpreted seismic lines, imported structural maps or
fault sticks. The dip, azimuth, length and shape define the fault
planes by the means of Key Pillars. The Key Pillars build the
framework of the 3D model, hence the name Key Pillars. A Key
Pillar is a vertical, linear, listric or curved line consisting two,
three or five shape points representatively. The figure in the
upper right corner shows a listric Key Pillar consisting of one
top, one middle and one base shape point. Every fault has to be
defined by Key Pillars to be included in a 3D grid. Faults might
be crossing, branching and vertical truncated and the intersections of the faults must be
connected in the fault modeling process. The fault model is complete when all faults are
represented by Key Pillars and been properly connected.
Important icons used in the process steps:
Select/Pick mode
Select shape point
Create fault from fault polygons
Select pillar
Add to or create fault from selected fault sticks
Connect two faults
Create fault from fault sticks, surface or
interpretation
Add pillar to end
Add new pillar by one point
Add pillar between
Add new pillar
Branched faults
Snap selected shape point
Crossing faults
Move along line tangent only
Linear pillar
Listric pillar
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A) Define a new model
Before building a 3D grid in Petrel, it is necessary to define a model. The new model only
contains empty folders. When you begin generating Key Pillars, they will be placed in one of
these pre-defined folders.
Steps
1.
Double click on Define Model
in the Process Diagram.
A window will pop up (Process for Define Model).
2.
Call the model GeoModel and click OK. The model will be placed
under the Models tab in the Petrel Explorer.
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B) Create faults based on fault polygons
A fault polygon is the line of intersection of the fault with the structure surface. To build Key
Pillars from these polygons they must have Z-values related to the surface they belong to. In
an earlier exercise you assigned Z-values from structure grids to these polygons. To build
Key Pillars from these polygons the polygon lines must represent a single fault (not multiple
faults).
Steps
1.
2.
3.
Activate the Fault modeling
process in the process diagram.
Display the fault polygon files in the fault polygons folder in the 3D window.
Select which fault to be modeled and set the suitable pillar geometry; vertical, linear, listric or curved
. Depending on the type of fault to be modeled.
4.
Open the settings for the fault model process by double
clicking on the process in the Process Diagram. Use the
default settings. However, the fault model should represent
the input data properly. Note the option to extend the Key
Pillars above the given min point and below the given max
point of the input data. You can control how far Pillars are
extended.
5.
Click on the Set Select/Pick mode
icon in the
Function bar
In the 3D window select all fault polygons that describe
one fault by clicking on the fault polygons and on the
Shift Key.
6.
7.
8.
Click on the Create faults from polygons
icon in the Function bar to generate Key Pillars along the
selected polygons.
The new fault has been added under the Fault folder in the Model tab of Petrel Explorer and called
“Fault 1”. You can change the name to a more appropriate name by clicking twice on the “Fault 1” and
changing the name under the Info tab of the window that
pops up.
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C) Edit Key Pillars
The Fault Modeling and hence editing of Key Pillars is a very important step in making an
accurate and reliable Petrel model. The Key Pillars should describe the fault planes as
defined by the input data. It is possible both to edit on a complete fault, a single Key Pillar or
a shape point in X, Y and Z directions, which makes the editing on faults very flexible.
Automatically constructed Key Pillars are often malformed and often it is needed to add new
Pillars to the end then modifying their shape. Use the tool for Adding Pillars at the end of
fault
. You will have to insert Key Pillars between
existing pillars when a fault's
shape contains more detail than the existing Pillar spacing can represent. Editing of shape
points and/or entire Key Pillars will be required to more closely fit the input data. This
editing may require adding more shape points to the pillar to achieve the desired form. All
Key Pillars in a fault don’t necessarily need the same number of shape points.
Steps
1.
2.
3.
4.
5.
6.
Editing is done in a 3D window.
The faults (Key Pillars) to be edited must be displayed. You may want to only
display only a few faults when editing or when performing particular editing
steps.
When editing, display available input data to use as a guide. Be sure that the
fault polygons or other data used to create the Pillars are visible in the 3D
window.
It is easier to see and edit faults when the plane between Key Pillars is filled with
color. To do this, click on the Toggle fill
icon. Be aware that it may be more
difficult to select items by clicking when the color fill is turned on.
The tool used for moving points and lines in Petrel is the widget. When you have
selected a Key Pillar by clicking on one of the shape points the widget will
appear. It consists of a plane and a cylinder. Click on the plane to edit in a plane normal to the cylinder
and click on the cylinder to edit along the tangent of the cylinder. You have to be in the Select/Pick
mode
to select a shape point. The widget is displayed to the right.
Press the left mouse button on the widget and move the Key Pillar or the Shape Point.
7.
Make sure the Move along line tangent only
tool is active. This tool limits the movement to the
tangent of the Key Pillar and it is a very intuitive way of editing the Key Pillars. Se figure below.
8.
To select only one shape point make sure the Select shape point
9.
To select an entire Key Pillar make the Select pillar
icon active. If you click on the line between
Key Pillars all shape points at that level will be selected (if you have the "Select shape point" icon
active).
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10. If you click on the line between Key Pillars while having the "Select pillar" icon active, all Key Pillars
will be selected. To select only a few Key Pillar/shape points, click on those that you want to select
while pressing the shift key.
11. Check the fault model by displaying the top and base horizons that all Key Pillars for the faults are in
correct position with the correct dip. If not, edit them as described above.
Continue Building Key Pillars from Polygons
1.
2.
Repeat the steps described above for building Key Pillars from polygons and do the necessary editing.
Remember to de-select the active fault when creating a new one. Otherwise, the new fault will be
attached to the previous active one.
If two faults are terminating against each other in the lateral direction you must join them by using the
Connect Two Faults
icon, described in the following section.
D) Connect faults
If a fault is truncated by another fault in the horizontal direction, it MUST be connected to
that other fault. This means that a common Key Pillar between the two faults must be
defined. You can either use a Key Pillar that already exists and edit it into a position so that it
fits both fault planes, or you can add a new Key Pillar between two existing Pillars and use
that as the common/connected Key Pillar.
Remember that the purpose of making Key Pillars is to get a definition of the fault plane. The
Key Pillars can be oriented in any direction as long as they preserve the dip of the fault plane.
Save your Petrel project before starting this activity. You could even make a copy of the
model so that if things get messed up with a fault you have a copy to replace the problem
with. Copy a model just like you do a file; select the model and press Ctrl C + Ctrl V.
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Join all the faults that should intersect one another. Remember to edit the Key Pillars that are
to be joined
Steps: Connect faults
1.
2.
Choose the two faults to connect. Make sure that the vertical extension of the two connecting Key
Pillars is fairly similar so that they join without significant contortion of the subordinate fault.
Zoom in on the area where the two faults are to be connected
3.
Select the two Key Pillars you want to connect using the Select/Pick Mode
4.
Click on the Connect Two Faults
icon and the Shift Key.
icon and define how you want to connect them.
Steps: Disconnect faults
The undo button does not work for connected Key Pillars, disconnect them instead.
1.
Select the two Key Pillars that should be disconnected
2.
Click on the Disconnect fault
icon
Steps: Create branched and crossing faults
1.
Select the Key Pillar where you want the crossing or branching fault to
be initiated from.
2.
Click on either the Branched Faults
3.
icon to generate a new fault.
Continue building the new branched or crossing fault by adding new
Key Pillars or merge it with an existing one.
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icon or the Crossing Faults
Geophysicist El-Sayed Fathi Mubarak
E) Create faults using selected fault sticks
Fault sticks are generated in Petrel or another seismic work station. These sticks represent the
fault surface and are converted to Key Pillars in this exercise.
Exercise Steps
1.
2.
From the Input Tab display the fault sticks in the “For Create from selected FS” folder.
Select Vertical, Linear, Listric or Curved Pillars depending on the type of fault you are modeling.
3.
Click on the Set Select/Pick mode
icon in the
Function bar.
Select some of the fault sticks on a fault by clicking on
the fault stick and the Shift Key.
4.
5.
6.
7.
8.
Click on the Create faults from selected fault sticks
icon in the Function bar to generate Key Pillars along the
selected fault sticks.
Once you have created the Key Pillars for a new fault, do
the necessary editing and by following the steps as
described under the exercises above.
Connect the faults where necessary.
Continue modeling the faults in the folder.
F) Create faults from all fault sticks
It is possible to select the entire set of fault sticks representing one fault and make Petrel use
every n’th fault stick as input. This is a fast approach but it requires that the fault stick are
representative of the fault, i.e. do not contain lots of “noise”.
Steps
1.
2.
From the Input Tab display the fault sticks in the “For Create from FS” folder.
Select Vertical, Linear, Listric or Curved Pillars depending on the type of fault you are modeling
.
3.
4.
Click on the Set Select/Pick mode
icon in the Function bar.
Select of the fault sticks on a fault by clicking on the fault stick. Make sure the Petrel Explorer input tab
is open and confirm that the fault you have clicked on in the 3D window is highlighted in Petrel
Explorer.
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Geophysicist El-Sayed Fathi Mubarak
5.
6.
7.
Click on the Create fault from fault sticks, surface or interpretation
icon in the Function bar to
generate Key Pillars along the selected fault.
Once you have created the Key Pillars for a new fault, do the necessary editing by following the steps
as described under the exercises above.
Connect the faults where necessary and continue modeling the faults in the folder.
G) Automatic generation of faults
So far the fault sticks have been generated one by one. In this exercise you will learn how to
automatically create Key Pillars from all sets of fault sticks in a folder in the Petrel Explorer
Input tab.
Steps
1.
2.
3.
4.
5.
6.
Convert one set of fault sticks to Key Pillars:
a.
In Petrel Explorer find the fault sticks folder called “For Convert to fault”. Open the folder and
right click on one of the fault sticks. Select Convert to fault(s) from the appearing pull-down
menu.
b.
Note the new fault in the 3D window and under the fault folder under the model.
This operation can be performed for all fault sticks in a folder:
a.
To avoid double sets of faults, delete the fault created above by selecting the whole fault in the
3D window or marking it in the models tab of Petrel Explorer and then press delete.
b.
Right click on the folder called “For Convert to fault”. Select Convert to fault(s) from the
appearing pull-down menu.
Continue doing the necessary editing of Key Pillars as described above.
Connect faults where necessary.
Click on the Execute button.
Observe that all the Key Pillars
will be cut by or extended to the
Base Cretaceous level, generating
smooth transitions between Key
Pillars.
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Digitize Key Pillars using 2D structure grid
Key Pillars can be created by digitizing the X-Y locations of shape points and capturing their
Z-value from a 2D structure grid. Normally the highest structure grid is used to create the
shape points for the top of the Pillars and the lowest structure grid to create the shape points
at the base of the Pillars.
Steps
1.
2.
3.
Display in the 3D window the top 2D surface grid (Top Tarbert) and the already built Key Pillars.
Zoom in on one of the big faults that does not have a Key Pillar built for it yet.
Remove the other Key Pillars from the display.
4.
Digitize the top shape points for the Key Pillars using the Add new pillar by one point
icon.
Remember to space the Pillars as far apart as possible while still capturing the curvature of the fault.
Display in the 3D window the base 2D surface grid (Etive).
Digitize the base shape points for the Key Pillars
using the snap the selected shape point method.
5.
6.
7.
8.
Active the Snap the selected shape point
icon
the toolbar. In the 3D window click on a base shape
point and snap it to the base surface by clicking on
it.
Continue until all base shape points have been
snapped to the surface. Display the grids to quality
control the result.
Edit and connect the faults. The top shape points
need to be extended above the Base
Cretaceous surface.
.
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Digitize Key Pillars on a general intersection
Faults can be digitized directly on a section, cutting through the model. Such an intersection,
called a general intersection in Petrel, can be oriented in any direction in 3D and moved
through the model. This is a method that will typically be used if fault sticks or fault
polygons do not exist.
Steps
1.
4.
Display e.g. the top Etive surface and all the fault in the fault model. Find a fault not represented by a
fault model.
Display a General intersection in the 3D window and move the general intersection perpendicular to
this fault.
Display all the surfaces on the intersection using the Enable/disable toggling of visualization on
intersection plane
icon.
In the Petrel Explorer Model tab, ensure that no other fault is active in the model.
5.
Select type of pillar
6.
Digitize the Key Pillars by using the Add new Pillar
icon. Petrel will generate a new fault in the
Fault model.
Move the intersection to start digitizing another Key Pillar on the same fault.
Continue to move the intersection and digitizing Key
Pillars until a fault has been created.
2.
3.
7.
8.
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Geophysicist El-Sayed Fathi Mubarak
Pillar Gridding
The Pillar Gridding process is the generation of a spatial
framework. In this exercise you will generate skeleton grids
based on the Key Pillars as defined in the previous exercise. The
Key Pillars will be converted into fault surfaces that are defined
by Pillars. Pillars will also be inserted in between the faults and
as such, define the grid cell size in the I and the J directions.
You will learn how the skeleton grids are generated and how it is
possible to apply trends and directions to improve the quality of
the grid. The grid cell size (increment) in the I and the J
directions will be specified. The final step will be to perform a
quality control check on the generated skeleton grids by playing through it in the I and the J
directions. The skeleton grids will be divided into segments separated by faults and
boundaries. Each segment will have a specific number of cells, which can be changed to
make the grid density higher or lower for specific segments.
The generated skeleton grids, also called pillar grid, defines the spatial framework into which
the horizons will be inserted later. This means that the pillars are not associated with Zvalues. The three skeleton grids that are created do not represent surfaces. Rather, they
represent the position of the pillars at the top, middle and base levels.
In the next process (the Make Horizon process) will the horizons be inserted and connected
to the pillars, and cells in the z-direction will be defined. A 3D grid will first be generated
after this process has been completed.
The goal of the Pillar Gridding process is to create evenly distributed rectangular shaped grid
cells.
Important icons used in the process steps:
Create boundary
Set part of grid boundary
Create boundary segment
Set part of segment boundary
Set I-direction
Set no boundary
Set J-direction
Set no fault
Set arbitrary direction
New I-trend
New J-trend
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Steps
In the 3D window display all the faults in the fault model.
9.
Ensure that all faults intersecting are connected properly. Laterally connected faults
should have a shared (gray) Key Pillar.
10. Check and see that a fault is not represented twice in the model.
11. The transition between all the neighboring pillars should be smooth.
12. Faults represented by Key Pillars should not cross each other. Display in the faults in the
3D window with the Toggle fill
. Check all faults and ensure that the triangulated
surface between the different Key Pillars is not crossing.
H) Create a new 3D grid
Pillar gridding creates the first component (pillars) of a
3D grid. Because of this the process must either create
a new 3D Grid or write over the top of an existing one.
When updating a model you should overwrite an
existing 3D Grid because the settings will already be
set from previous executions and make the update
easier. The best way to do this is to copy the 3D Grid
and overwrite the copied version.
Some key settings such as name of the 3D grid and the
grid increment are set when initializing the Pillar
Gridding process, although they can be altered at any
time.
Steps
13. Start the process of creating a new 3D Grid.
Note that when you double clicked on Pillar
Gridding in the Process Diagram, a 2D
window opened with your fault model
displayed. The line is the projection line
between the Key Pillars mid-points you
defined in the previous exercise. The dots are
the mid-point on the Key Pillar it self.
14.
Enter a name for the 3D grid (3D Grid) and specify the I
and J increment (100).
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15. Move the Pillar Gridding window out of the
way but leave it up, as it will be used
repeatedly in the following exercises.
I)
Create a simple grid boundary and quality check
your fault model
The boundary marks the lateral extent
of the 3D grid. It can be defined
interactively in a number of ways. The
boundary may completely enclose the
faults or it may cut across faults.
Alternatively faults can form part of the
grid boundary. The 3D Grid is only
defined inside the boundary. Therefore
no volumes, structural horizons, or
attribute cells will be calculated or exist
outside the boundary.
To completely enclose all faults in the
3D grid the tool for Create boundary
can be used. This option is used for
digitizing a boundary in the 2D
window.
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Steps
16. Display one of the time surfaces in the input tab of Petrel Explorer in the 2D window.
This will be used as a guide when digitizing the boundary.
17. Start creating a boundary around the area of interest by using the icon Create boundary
and click with the left mouse button to draw a boundary. Double click on the left
mouse button to close the boundary.
18. Build a 2D grid (QC check) by double clicking on the Pillar Gridding process in the
Process Diagram and pressing Apply. If the boundary is not closed, then close it. Key
Pillars that are crossing each other will be marked with yellow dots. If this is so then go
to the Window menu and Tile Vertical the 3D window with the fault model displayed
and the 2Dwindow with the Pillar grid displayed. The problem pillars will be displayed
in the 3D window as well, activate the Fault Modeling process and fix the problem by
editing the Key Pillars. Run the Pillar Gridding process over again.
J) Create a segment grid boundary
Steps
19. Display one of the time surfaces in the input tab of Petrel Explorer in the 2D window.
This will be used as a guide when digitizing the boundary.
20. Start by making faults, on the left side of the area, part of the boundary. Use the Set
Select/Pick mode
to mark a fault. Note that when clicking on the line connecting the
shape points on the fault (the dots) the whole fault becomes yellow. This means that the
fault is selected and you can give it a purpose. Alternatively you can press one shape
point (start point) hold the Shift key and press the end shape point (the start and end
shape point turn yellow).
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21. Click on the Set part of grid boundary
icon. Note that the fault or the part of fault
will be marked with a double blue line, as shown in the figure below.
22. Continue the boundary from fault to fault (digitizing points in between) on the south,
east, and north sides of the boundary.
23. Select the Create Boundary Segment
icon.
24. Click on the point on a fault to start digitizing the boundary from.
25. Digitizing the boundary between the faults so it matches the surface displayed. You can
digitize anyway you like but you can not cross faults.
26. Click on a shape point on a fault to end the boundary.
27. Continue to set the boundary for the rest of the area.
28. Build a 2D grid (QC check) by pressing Apply. If the boundary is not closed, then close
it. If Key Pillars are crossing, then go back to the Fault Modeling process, change the
view to 3D display and edit the Key Pillars so that they are no longer crossing. Press
Apply over again.
Faults have to be deleted and edited in the 3D window using the Fault Modeling process. But
trends can be edited and deleted as described above.
K) Insert directions and
trends
Fault I- or J-directions are terms used by
Petrel to identify faults that exert strong
control when Pillar Gridding. Fault directions
may be of three types: Arbitrary, I, and J.
Arbitrary direction is the default setting for
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all faults. I direction (faults are colored green in the 2D window) is used for faults trending in
one direction. J-direction (faults are colored red in the 2D window) is used for faults trending
orthogonal to the I-direction. During Pillar Gridding faults designated as either I or J will
have sides of the final cells oriented parallel to their fault surfaces and the surface will make
up one side of adjacent cells. Arbitrary fault surfaces will also make up one side of adjacent
cells. However, the other side of the adjacent cells and the sides of other nearby cells will not
be oriented parallel to these faults. This means that the geometric form of cells adjacent to
arbitrary faults is very non-orthogonal and the form of cells adjacent to an I- or J-directed
fault is close to orthogonal.
Trends are lines, created by you, that improve the quality of the grid. Trends act just like I- or
J-directed faults during Pillar Gridding, implying that like trends and directions should be
aligned parallel to each other (I || I, J || J, I _|_ J). A trend can be inserted to guide the
gridding process. If you insert a green trend it must be parallel to the green directions, and a
red trend must be parallel to the red directions.
General guidelines:
 Start simple, preferably with no directions, and insert directions only where
necessary.
 Red (or green) directions and trends should be parallel to each other.
 Red directions should be perpendicular to sets of green directions and visa
versa.
 The space between like directed faults should be about the same along the
length of the direction.
 Do not make two faults the same direction
if they are wide apart at one end and close
together in the middle or at the other end.
The number of cells between two directed
faults of the same type (both I or both J)
will remain the same over the length of the two faults. Therefore, if the two
faults come together the size of the cells gets very small to allow the number
of cells to remain the same.
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 Do not make part of one fault an I-direction and the rest of the fault a J-
direction.
 Do
not
put
in
to
many
similar
directions
too
close
together.
Steps
29. Look for the overall fault pattern in the 2D window. In this case the major faults are
oriented North-South. Give the main fault(s) aligned North-South a red J direction. With
the Select/Pick mode
icon select the line between the shape points to select the fault
and press Set J-direction
icon.
30. Give a perpendicular fault a green I direction, selecting the faults in the same manner as
above and pressing Set I-direction
icon.
31. Press Apply in the process window and observe the changes in the mid skeleton grid.
Note that the cells along the directed faults are aligned parallel to the fault whereas the
cells along the arbitrary fault (white) are cut towards the fault.
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32. Continue to set directions to all major faults in the project.
33. Insert a trend in the I direction (green) between two J directed faults (red), similar to the
left figure below.
34. Press Apply and observe how the cells are aligned along the trend line (right figure
above).
35. Make sure that the direction and trend alignment are ok by QC the mid-skeleton grid in
the 2D window. Add directions on faults and trends to refine the mid-skeleton grid.
.
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L) QC of Skeleton grid
You should always do a quality control check after the skeleton grid has been generated. The
important steps during QC involve checking for crossing pillars. Crossing pillars will
generate negative cell volumes. If you find crossing pillars, you must either do the Pillar
Gridding over again and use directions and/or trends to avoid the crossing pillars, but most
likely you will have to go back to the Fault Modeling process and adjust the Key Pillars.
The reason why the QC is important after the construction of the skeleton grids, even if the
mid skeleton grid was fine during the Pillar Gridding process, is because Petrel only checks
for crossing pillars for the mid skeleton when Pillar Gridding. When extrapolating the pillars
to create the top and base skeleton, Petrel will not check for any crossing pillars.
step
36. Activate the project in the Model tab of Petrel Explorer.
37. Open the Skeleton folder in the newly created 3D grid.
38. Perform a visual check of the grids individually in the 3D window, look for spikes and
irregularities. The comments below describe what to look for.
39. Display the Key Pillars from the fault model to locate the problem.
40. In the 3D window display a J-intersection from the “Intersections” folder. Click on the
name to make it active.
41. Double click on the intersection folder and toggle on show pillars in the style tab settings
window.
42. Use the player
to move the intersection along the grid. Check the
pillar geometries for crossing pillars.
43. Perform the necessary corrections on process the fault model to improve the skeleton
grids (you will have to run the Pillar Gridding again).

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Make Horizon
In this exercise you will insert horizons into the 3D Grid (Skeleton framework). This is
the first step in the vertical layering. This is the first step in the vertical layering workflow.
The vertical layering involves:
 Make
Horizons: Inserting
horizons in the 3D gird
the
 Depth Conversion: The horizons are
in
time, so depth conversion is
necessary to move them into the
depth domain.
 Make Zones: Isochores will then be
used
to create zones between the major
horizons.
 Layering: Create the fine scale layering that represents the cells of the model.
In addition to the mentioned processes, you will learn editing techniques. These include the
Edit 3D Grid procedures and how to force-tie horizons to well tops near faults.
The Make Horizons places all horizons defined directly from structure data into the 3D Grid.
This normally includes unconformity surfaces and primary horizons within sequences. Input
for these horizons may be 2D structure grids, interpreted line data from a seismic
workstation, well tops, or other point or line data. The 3D Grid these horizons are to be
placed into consists only of pillars defined in the Pillar Gridding step. These pillars define the
corners of the cells that will ultimately be created in the 3D Grid. Values are interpolated at
each pillar based on nearby input data for the horizon. These interpolated values define the
surface in the 3D Grid.
M) Define the 3D grid domain
The domain (time or depth) setting guides Petrel in performing certain actions, such as
whether to tie to well tops at this step or in the Depth Conversion step. Therefore, the 3D
Grid's domain needs to be set by you to match the units of the surfaces it will contain. In this
exercise the inputs are in time.
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Steps
44. Open the settings window of the 3D grid by doubling clicking on the 3D Grid name.
45. Set the domain to time under the Info tab.
N) Insert the horizon into the 3D skeleton grid
Pillar gridding creates the first component (pillars) of a 3D grid. The user must either create a
new 3D Grid or write over the top of an existing one. When updating a model you should
overwrite an existing 3D Grid because the settings will already be set from previous
executions and make the update easier. The best way to do this is to copy the 3D Grid and
overwrite the copied version.
Some key settings such as name of the 3D grid and the grid increment are set when
initializing the pillar gridding process, although they can be altered at any time.
Exercise Steps
46. Double-click on the Make Horizon process. A dialog will pop up. Select the Horizons tab as it contains
the
primary
controls
for
making
horizons.
47.
Use either the Append item in the table
icon or the Set number of items in table
icon located near
the top of the dialog to insert one or several new rows into the table. Create as many rows as you have horizons
to
build
(check
the
Petrel
Explorer,
Input
tab).
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48. Select the data to use to create the horizon - Do this by highlighting the file's name (make bold) in the
Petrel Explorer and then clicking on the blue arrow to the left of the Input #1 column. Insert four
horizons as shown in the figure below. Use the 2D time surfaces (Base Cretaceous, Top Tarbert, Top
Ness, and Top Etive). Rather than insert each horizon separately, all can be inserted at once using the
following approach.
a.
Right-click on the folder containing the 2D surfaces and select ‘Sort the files by depth’
b.
In the Make Horizon process, toggle on ‘Multiple drop’. This allows you to drop a range of data
by only selecting the first in a row.
c.
Select the Base Cretaceous surface from the Petrel Explorer Input tab. Select it by clicking on the
name of the file (make it bold).
d.
Click on the blue arrow below Input #1, as shown in the figure below. All the input files will be
added in the correct order.
49. For each horizon do the following:
a.
Define the horizon's geologic character (stratigraphy) - Do this by clicking on the row's box
under the "Type" column. Set Base Cretaceous to be erosional and the other surfaces to be
general.
b.
Select the time picks to tie the surface to. Do this by highlighting the file's name (make bold) in
the Petrel Explorer and then clicking on the blue arrow to the left of the Well tops column.
50. Select the Settings Tab - to define parameters controlling interpolation and extrapolation parameters.
This is where the influence of points that have been locked during editing is specified. Refer to the
online Petrel manual for details of each parameter. For the introduction course, use the default.
51. Go to the Faults tab. All the faults that you incorporated in the Skeleton grid when doing the Pillar
Gridding are listed here. Set the fault distance to 2 for all the faults. For further information see
comments below.
52. Select the Wells Tab - to access parameters that control how top picks are used during the well tie
process. Refer to the online Petrel manual for details of each parameter. Use the default settings for the
introduction course.
53. Press OK.
54. In the Models tab you will now find four new horizons in the horizon folder. Display the generated
horizons and QC the fault cuts.
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“Drag” into the fault plane
Not using all available data to build Key Pillars or sloppy construction of the input data will
create poorly defined faults. A poorly defined fault will often cut into structure data on one
side of the fault, incorrectly placing that data on the other side of the fault. When the data is
used to build a horizon it creates what appears to be structural ‘drag’ into the fault plane.
The Fault Distance can be used to blank input structure data near faults. This will eliminate
the problem although the correct solution is to fix the fault model. Fault Distance is defined
in number of grid cells. Petrel sets data in the area, from the fault plane out to a specified
number of grid cells, to undefined (deleted). During the gridding process the horizon is
extrapolated into this blanked area based on the trend of the unblanked data.
If you get a drag towards the fault plane, it will usually help to increase the fault distance for
that fault. Caution should be taken as data along the entire length of the fault is deleted.
There are three ways to fix this:
55. In the Fault tab in the Make Horizon Process window give different distance from faults values for the
different faults in the grid. To determine which fault to adjust, display the faults and while in the
Select/Pick mode
click on the fault plane. Information about the name of the fault will appear in the
lower right corner of the window. For the fault in question, increase the value that is stored in the
Distance column. This will usually involve changing it from 0 or 1 to 2 or 3.
56. Eliminate the data from both sides of the fault near the fault. The distance for deletion is defined in
terms of 3D grid cells.
57. Correct the fault model if possible.
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Depth Conversion
The fault model and 3D grid have been built in time and need to be converted to depth.
Currently only three depth conversion processes exist in Petrel:
 Linvel (V = Vo + kZ)
 Linvel (V = Vo + k(Z - Zo)
 Constant (V = Vo)
Where: both Vo and k can be either constants or surfaces.
In addition to the horizons that are being depth converted, other surfaces, such as seabed, can
be used as input for the depth conversion process. This means that the interval velocities can
exist between a datum and seabed, seabed to top reservoir, etc.
During the depth conversion process the converted grids can be tied to well tops. This is done
on a tab separate from the Intervals Tab where most of the parameters are set and is easy to
miss. If missed, the depth conversion is simply rerun with the tops selected, overwriting the
previously built 3D Depth Grid.
Output from the depth conversion process is a new 3D Grid named the same as the input but
with the letters (DC) appended to the name. This 3D Grid is now in depth and is used from
this point on in the Petrel modeling process. If problems are found with top picks, faults, or
modifications to the primary horizons are made, then changes are made in the time domain
and the steps up to and including depth conversion rerun.
When all the depth conversion process is run a Velocity Model that contains all the depth
conversion settings will be created and stored under the Velocity Models sub-folder under at
the very top of he model. If you create a 3D grid later on, the same depth conversion settings
can be applied. If you want to use different depth conversion settings, then a copy should be
made of the velocity model before entering the Depth Conversion process.
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Geophysicist El-Sayed Fathi Mubarak
Exercise Steps
Several velocity models may be created in a Petrel model. By clicking with the right mouse
button in the Petrel Explorer on the folder called Velocity Models, the user can open a menu
and from there insert a new velocity model. It is always the model that is bold that will be
used when the depth conversion process is executed.
58.
59.
60.
61.
Double-click on the Depth Conversion Process in the Process Diagram to open the settings dialog box.
Fill in entries under the Intervals tab according to the table below:
Find the Seabed time surface under velocity data in the Petrel Explorer Input tab.
Expand the Horizon folder of the time grid. Click on Base Cretaceous and drop it into Top Time
Horizon for all intervals in the 3D grid.
62. Change the Velocity set up according to the set up shown below. The velocity surfaces are located in a
Velocity Data folder in the Input tab.
63. Go to the Depth Well Tops tab and insert the well tops from the Well Tops folder in the Input tab using
the blue arrow.
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Geophysicist El-Sayed Fathi Mubarak
64. Go to the Wells tab, and choose Well Adjustment Inside segment only. Select Make Well Report and
Reset
sheet.
Click
on
Use
influence
radius
and
specify
a
well
radius.
65. Click OK to run the depth conversion process. When it finishes, check the well report to inspect the
depth residuals.
66. A new 3D grid has been created. It has the same name as your time grid, with the (DC) added to the
end. Make this 3D grid active by selecting it in the Petrel Explorer. Do this before moving to the next
step so that isochores are added to the depth model and not the time model.
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Make Zones
The Make Zones process is the next step in defining the
vertical resolution of the 3D grid. The process creates zones
between each horizon. Zones can be added to the model by
introducing thickness data in the form of isochores,
constant thickness and percentages. Well points can also be
used to tie top structures to the well picks. This process step
may be skipped when no zonation is given.
O) Create Zones
This is the process of inserting geological zones in the stratigraphic intervals above, inbetween and below the horizons that were inserted in the Make Horizons process. The zones
are typically created based on isochore grids, constant values or built proportional from
existing horizons. Well tops can be used for well adjustment of the horizons that will be
created.
Exercise Steps
67. Make sure your depth converted grid is active.
68. Double click on the Make Zones Process step in the Process Diagram. A dialog window will pop up.
69. Select the Stratigraphic interval to be worked first. This interval will be completed (parameters
specified) and the Apply button must be pressed before moving to the next interval.
70. For the Top Tarbert - Top Ness interval there are three isochores. For the Top Ness - Top Etive interval
there are two isochores.
71. For each stratigraphic interval:
a.
b.
c.
d.
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Use either the Append item in the table
icon or the Set number of items in table
icon
located near the top of the dialog to insert rows, related to one or several isochores, into the table.
Create as many as you have isochores to insert.
Select data objects e.g. isochores and well tops from the Input tab.
Insert the isochores and well tops by clicking on the blue arrow next to the input field called
Input.
Name the isochores and new horizons - The horizon name defaults to "Horizon" unless top picks
are selected (sub-interval type = Conformable) and then it defaults to that name. The isochore
name defaults to "Zone" unless a 2D Isochore Grid is selected and then it defaults to that name.
The names can be edited at any time.
Geophysicist El-Sayed Fathi Mubarak
e.
f.
g.
h.
Select Build from base horizon and distribute the volume correction Proportionally among the
various sub intervals.
Select to do the thickness calculation Vertical Thickness.
Go to the Settings tab and de-select the option that says: ‘According to the settings in the “Make
Horizons” process. Use the settings in the “Wells” tab’. If you don’t de-select this option you will
not get a well report.
Under the Wells tab, specify that you want to create a report.
i.
Press Apply to generate the
intermediate horizons and
zone.
72. Repeat the procedure for all
Stratigraphic intervals.
P) Using Intersection planes for QC
The Intersection Plane is a vital tool for visualization and quality controlling Petrel models.
Playing through the 3D grid with different properties using an intersection plane is a very
efficient method for quality check and increasing understanding of the models.
Exercise Steps
73. Display the base horizon of the Petrel
model in the 3D window.
74. Go to Intersections folder and active e.g. a
J-direction (click on its name till it is bold).
75. Check the box to view the intersection in
the 3D window.
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Geophysicist El-Sayed Fathi Mubarak
76. Click on the Player
to move the intersection. Note! The player will only
appear if the active intersection is displayed in the display window.
77. To stop the intersection from playing, click on the Stop icon
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Geophysicist El-Sayed Fathi Mubarak
Layering
The final step in building the structural framework is to
define the thickness and orientation of the layers between
horizons of the 3D Grid. These layers in conjunction with
the pillars define the cells of the 3D Grid that are assigned
attributes during property modeling.
The Layering process will only make a finer resolution of
the grid and no input data are used for this process. The user
can define the vertical resolution of the grid by setting the
cell thickness, define a number of cells or use a fraction
code. When specifying the cell thickness the zone division
can either follow the base or the top of the zone.
The layers should be defined based on the properties to be modeled. Usually, the layer
thickness should be the thickness of the thinnest facies to be modeled. However, it is
important to keep in mind that the number of cells increases when the layer thickness
decreases, so you should not put in more detail than necessary.
steps
78. Make sure that the model that includes the geological zones is active.
79. Double-click on the Layering process. A dialog will pop up.
80.
For each zone (identified by the name in the left column of the row), define your layering. Use a variety of Zone
Divisions.
81. Press Apply to see the result in the 3D window.
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