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Petrel: Structural Modeling
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Table of Contents 1 Pre-processing ........................................................................................................................................................... 5 Edit connected fault sticks ....................................................................................................................................... 5 Crossing fault sticks .................................................................................................................................................. 6 Cut fault sticks .......................................................................................................................................................... 7 2 Fault Modeling .......................................................................................................................................................... 9 Petrel fault types ...................................................................................................................................................... 9 Input data ................................................................................................................................................................. 9 Define model ................................. ................ ................................... ................................... ................................... ................................... ................................... ................................... ................................. ................ 10 Fault modelling process ......................................................................................................................................... 10 Editing key pillars ................................................................................................................................................... 11 Cut against surfaces ........................................................................................................................................... 11 Moving key pillars .............................................................................................................................................. 12 Automatic connection ........................................................................................................................................ 14 Connect faults manually .................................................................................................................................... 15 Add pillar to the end .......................................................................................................................................... 16 Disconnecting faults ........................................................................................................................................... 17 3 Pillar Gridding .......................................................................................................................................................... 18 Boundary ................................................................................................................................................................ 18 Existing polygon as boundary ............................................................................................................................ 19 Create boundary ................................................................................................................................................ 19 Make faults boundary segments ....................................................................................................................... 20 Create boundary segments ................................................................................................................................ 20 Remove boundary .............................................................................................................................................. 21 Trends and Directions ........................................................................................................................................ 21 Skeleton – Create grid ........................................................................................................................................ 23 Segments ................................................................................................................................................................ 23 4 Make Horizons ........................................................................................................................................................ 25 Generating Fault-Horizon Intersections for the 3D Grid .................. ........................... .................. .................. .................. .................. .................. .................. ........... .. 28 5 Depth Convert 3D Grid ............................................................................................................................................ 32 6 Make Zones ............................................................................................................................................................. 34 Generate Isochores ............................................................................................................................................ 34 Make Zones process ........................................................................................................................................... 36 7 Layering ................................................................................................................................................................... 39 Vertical Variogram Analysis - Correct layering ................. .......................... 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Introduction to Corner Point Gridding Aim to create a 3D reservoir model to understand and predict our reservoir by creating a celled model. Populate cells with reservoir properties from fr om up-scaled well control points. Workflow
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1 Pre-processin Pre-processing g It is good practice to make a copy of your data before you perform any processing on it. This way y ou may revert back to your original if you are unhappy with the results.
Edit connected fault sticks Fault sticks may appear as one continuous line.
Can use an operation to split in to individual fault sticks or scissor tool:
Operation 1) Use Measure distance tool to measure the length of the artificial ar tificial line 2) Double click on the fault and go to Operations tab. 3) Expand the Polygons operations folder and select Split by horizontal length . 4) Input the maximum horizontal length and select Run. Only one undo is available.
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Scissor tool 1) Open the Make polygons process in the ribbons tab at the top .
Open the Settings tab and toggle on ‘Delete point or line segment when cutting’
2) Select the Disconnect polygon icon
Crossing fault sticks For Corner Point Gridding, fault sticks need to be in the same direction. Need to remove crossed sticks.
from the tool pallet. Click on the lines to be removed.
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1) Activate the Make/edit polygons process in the Processes pane. 2) Use the Select/pick mode
tool while holding SHIFT to select the fault sticks you can to remove.
3) Use DELETE key or delete icon
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Cut fault sticks Cut fault sticks out of your area of interest using Operations.
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1) Open Settings for each fault. Navigate to Operations tab. 2) Expand Eliminate where folder and select Z> or Z< Surface (x,y) . 3) Insert Surface to cut sticks against. 4) Select Run.
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2 Fault Modeling Generate main faults by generating “key pillars”. Pillars form the base of generating a 3D grid
Petrel fault types Fault types are based on the t he number of shape points.
Input data Faults can be generated based on: Fault sticks Fault polygons Faulted surfaces Seismic interpretation interpretation Seismic Cross section Well cuts
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Define model Click on the structural modelling tab on the ribbon. The workflow order is the same as t he processes seen along the ribbon. If a process is greyed gre yed out, it means the pre-requisite pre-re quisite for that process has not been carried out yet. Double click on Define model . Name your model to store the faults and all 3D grids related t o that fault model. When you click OK or Apply it will be stored in your Models pane.
Fault modelling process 1) Make active your model in the Models pane. 2) Activate geometry to be used in function bar 3) Right click on Input data folder and select Convert to faults in fault
model…
. every nth stick to build pillar on and maximum search distance to nearest neighbour pillar 4) Select
5) View results in model
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Editing key pillars Cut against surfaces Once faults have been modelled, Fault modeling process c uts faults against a top and/or base limit.
1) Open Fault modelling operation in the ribbons tab 2) Select top and base limit. Drop in surfaces to cut against. 3) Select parameters. 4) Select Cut/extend.
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Results:
Moving key pillars
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1. Display the fault in a 3D window. 2. Select the Manipulate pillars/shape points tool in the Fault model Tool Palette . 3. Select (Shift for multiple) key pillars or shape points to manipulate. To move the pillar vertically, select the cylinder and drag it vertically:
To move the pillar laterally, select the square plane and drag it in any direc tion:
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Automatic connection Faults that are close but not touching each other need to be connected to build a lattice for the Pillar gridding process.
1) Open Fault modelling operations along the ribbons tab. Navigate to Operations tab. 2) Set the Extend distance to tell Petrel the distance it should search for another fault. 3) Set the Remove distance to tell Petrel the pillars that are closer than t his distance to the connection pillar after a connection has been made will be removed. 4) Select ‘Only use visible faults’ if you want to apply it to specific faults in view
5) Select Auto connect.
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Connect faults manually 1) Choose faults to connect. Identify areas to connect. Make sure vertical e xtension of connecting pillars is similar so as not to cause significant contortion of t he subordinate fault. 2) Select two key pillars from each fault to join using the SHIFT key plus the left mouse button to select multiple pillars:
3) Select the Connect two faults icon
by right mouse button click on the fault pillar
4) Select how you want to connect the faults in the Connect pillars dialog box:
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Add pillar to the end You may need to add a pillar to the end of your modelled fault to be able to connect it to another fault for example. In this case, select the end pillar of your fault and select the Add end pillar to fault icon mouse button click on the fault pillar
by right
Add pillar in between pillars To add a pillar between two existing pillars, select the two pillars you wish to insert a pillar in between and selec t the Add pillar between icon
when right mouse button click on the fault pillar
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Disconnecting faults You may have a modelled fault which you believe should be tre ated as two separate faults for example. ex ample. In this case, select the two pillars which represent the end of each fault and select the Disconnect fault icon
You will see a new fault created c reated in your model.
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3 Pillar Gridding Pillar gridding is the process of making a skeleton framework in order to create c reate a celled model. To create a 3D skeleton, first create a 2D mesh mid skeleton grid that connects the key pillars. This is defined by row and columns. Then extrapolate mid skeleton upwards and downwards to create the top and base skeletons in the third dimension. The 3D grid is defined by rows, columns and pillars positioned in the xyz.
First you need to create a boundary for your area.
Boundary You can use a fault or boundary segment to form parts of your boundary. Or you can use an existing polygon or create a new boundary around your area. It must be closed. First open a 2D Window and display the faults in your model.
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Existing polygon as boundary
1) Make the Pillar gridding process active. 2) Display your polygon. 3) Right click on your polygon and select Convert to grid boundary .
Create boundary 1) Open a 2D window, display uour faults & Make t he Pillar gridding process active along the ribbons tab 2) Select the Create external grid boundary icon 3) Draw your area of interest.
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4) Double click to close the boundary.
Make faults boundary segments 1) Activate the pillar gridding process by c licking on the Pillar gridding on the ribbons tab.. 2) Select the Set part of grid boundary icon to show is it part of the boundary.
to make that fault part of the boundary. The fault will turn blue
Create boundary segments
1) Make the Pillar gridding process active along the ribbons tab. 2) Select the Create external grid boundary segment icon
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3) Pick in between pillars to join the boundary
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Remove boundary Select part of your boundary and select the Set no boundary icon
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Trends and Directions Once you have a closed boundary, you can assign trends/directions. This is in order to guide the grid cell shape and orientation. Trends can be used as a segment divided when there are no faults. Trends and directions are defined in the i and j directions. This can be done before gridding. Or after to tune the grid. You can give direction to faults and assign t rends.
I- direction ………………. J- direction ………………. Arbitrary …………………. Set no boundary ……..
I-trend ……………………. J-trend ……………………
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1) Select a fault or part of a fault using the Select/pick mode . 2) Select the I-direction or J-direction icon to give direction to that fault. Your I-direction is your major direction.
To add trend, select the I-trend or J-trend icon and draw on the trend interactively:
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Skeleton – Create grid 1) Open the Pillar gridding process from the ribbons tab. 2) Name your grid. 3) Set your grid increment. A smaller increment gives a higher number of cells.
4) Select Apply to create the Mid skeleton grid. gr id. 5) Quality check the Mid skeleton. Tune using trends and direction (previous section). 6) When satisfied with Mid skeleton, select OK to create a Top and Base skeleton.
Segments Connected faults form boundaries of segments. In order to view individual segments either toggle on/off each segment in the Segment filter:
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Or double click on the Skeleton item in your grid to open the Settings. Navigate to the Style tab and to the Solid sub-tab. Select Show:As Segment . Select Apply:
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4 Make Horizons The purpose of this process is to ge nerate horizons in the 3D grid. This process is the first step in defining the vertical layering of the 3D grid. The layering can later be refined using the Make Zones/Layering process. 1. Double-click on Make Horizons process
2. In the Horizons tab click the Multiple drop
icon. This allows you to drop a range of data by
only selecting the topmost one in a folder. Select the top surface in the Input pane. Click on the blue arrow below Input#1. The input objects will be added and the Horizon column will be updated with the same name.
3. For each horizon, define its geo logical character, to do this click on the box in the Horizon type column and set the surfaces accordingly.
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4. To tie the well tops to surfaces, select well top from Well We ll Tops folder in Input pane>Stratigraphy and drop in the well tops, then select Multiple drop and insert using blue arrow.
5. Go to the Faults tab. All of the faults generated during Fault modelling are listed here. As default distance from the fault is set to 100 project units.
The distance must not exceed the influence area for the data such as fault compartment
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6. Go to the Well Adjustment tab and choose to make adjustments using well top data Across segments.
Click OK.
7. Open 3D window and display your horizons and Edges from your Models pane.
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Generating Fault-Horizon Intersections for the 3D Grid Sometimes the fault distance will not be e nough to sort out all of the problems caused by false drag or pinch out cells. To overcome this we can c reate fault-horizon lines. 1. Make a copy of the active 3D grid. 2. Open the settings for the surface (Models pane, Horizons folder), go to the Operations tab. 3. Select Resample from the 3D grid to the Fault Model and click Resample button. A new folder called Horizon fault lines is now generated. This folder is stored in the Fault model in the Models pane.
4. Activate the fault modelling process. 5. Display the fault model and the horizon lines in a 3D window, display your horizon. 6. If it is not matching the input data, make adjustments to the horizon lines by first using the select horizon nodes button from the function bar
and then either use the Select/pick mode
the nodes to move or use Add/Move horizon nodes on the active horizon
to manually select
in combination with
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Add/move horizon nodes at back side of the fault fault
or Add/move horizon nodes at front side of the
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The different sides of the fault are distinguished b y dotted lines (back) or solid lines (front).
Before
After
7. Open the settings for your horizon (Models pane) and go to Oper ations tab. 8. Select Resample from Fault Model to t he 3D grid and click Resample.
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9. For the edits to take full effect, make horizons process must be re -run. In the horizons tab, make sure to calculate horizons with Use horizon-fault lines selected.
10. In the Settings tab select the Lock all resampled horizon nodes check box.
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11. QC the result in the 3D window.
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5 Depth Convert 3D Grid 3D grids are depth converted by using the Domain conversion process under Corner Point Gridding tab along the ribbon. 1. Ensure that the correct grid is active in your Models pane as it is grid to be depth converted. 2. Click on Domain conversion.
3. Select the appropriate Velocity model (in this ex ample Velmod K(Z-Z0) Corrected) from drop down menu.
4. Alternatively change the pillar geometry types for faulted and non -faulted pillars. Click OK.
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5. A new 3D grid appears in the Models pane with the name of the input and velocity model extension. This 3D grid is in the depth domain as indicated by a blue icon in front of its name. 3D grids in time domain have an orange icon.
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6 Make Zones The make zones process is the next step in defining the vertical re solution of the 3D grid. Each zone is defined by two horizons. Zones can be added to the model by introducing thickness data in the form of isochores, constant thickness and percentages.
Generate Isochores 1. Go to the Input pane and expand the Well Tops folder and the St ratigraphy folder. Create isochore data for the Zone Lower Zone Top (i.e. Lower Zone Top to Base Sherwood).
a.
Highlight the top marker (i.e. Lower Zone Top )
b. Right-click on the base marker (i.e. Sherwood Base) and select Convert to isochore points
c.
The isochore points are created in the bottom of the Input pane
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d. Create isochore data for the other zones (repeat 1 a-c) 2. Double-click on Make/Edit Surface process. a.
Drop the isochore points into Main input.
b. Select the Thickness attribute from t he drop-down list in the Attribute field. c.
Click Suggest settings from input and select Isochore points/residuals.
d. Set the Automatic geometry in the Geometry tab. Click OK.
e. Create thickness surfaces for all isochore points. Generated surfaces are stored in the bottom of the Input pane.
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Make Zones process 1. Click on Make zones process in the ribbon, Zones subtab and select stratigraphic interval: in this example Top Sherwood_CJB-Base Sherwood.
a.
Click on Append number of items in the table zones in Multi zone settings window. Click OK.
icon and select 4 (or the amount you have)
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b. We use generated isochore surfaces as input in Make Zones process. c.
In the Input pane, select the thickness surface and insert in the appropriate zone by clicking on the blue arrow next to the Input field. Insert well tops between the isochores by going to Well Tops>Stratigraphy. Select the well tops that correspond with the stratigraphic interval you are working on.
d. Select Build from: Base horizon and distribute the volume correction as Proportional correction and build along Vertical Thickness (TVT). Click OK.
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e. Open new 3D window and visualise your Horizons and edges. You should see four zones you j ust created.
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7 Layering The final step in building the structural model is to define the thickness and orientation of the layers between horizons of the 3D grid. These layers, together with the pillars, define the ce lls of the 3D grid t hat are assigned attributes during property modelling. You can define the vertical resolution of the grid by setting the ce ll thickness, defining a number of cells or by using a fraction code. The layers should be defined based on the properties to be modelled. The layer thickness should be the thickness of the thinnest facies to be modelled. 1. Ensure the model that includes the geological zones is active. 2. Click on Layering process ain the Ribbon
3. For each zone, define your layering. Use a variety of Zone divisions. Specify the number of layers (Proportional), cell thickness (Follow top/base) or relative proportions (Fractions).
Proportional - Constant number of cell layers at every pillar of the grid. The cell layering will be somewhat conformed to both the top and base of the zone. Follow top - Cell layering parallel to the top of the zone. Follow base - Cell layering parallel to the bottom of the zone. Follow surface - Defines layers in the 3D grid parallel to a specific surface. It preserves the correct layering in eroded zones and enables a more accurate property distribution. Fraction - Layering, with user controlled proportional thickness of each cell layer.
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4. Display your layering in a new 3D window. As an example:
Fractions
Proportional
Follow top
Follow base
Vertical Variogram Analysis - Correct layering Analysis of variograms can be used to determine the required grid resolution. To aid in selecting the layer thickness, a vertical variogram can be mo delled for spatially varying properties immediately after performing the log upscaling. The main purpose is to extract an upper bound for the layer thickness for t he zone (i.e., 1/2x vertical range).
Layer resolution should be at or below ½ of the vertical range. 1. Select the Model grid to activate it. Open the Data analysis process and select the upscaled well log (porosity in the example below). Unlock the zone settings by clicking on the Leave settings unchanged icon
. Select the zone and use raw logs data
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2. Go to the Variograms tab (vertical (vert ical direction subtub in v2012).
3. Select the Toggle simbox mode off
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4. Set up a proper search cone parameters to compute the experimental variogram. -
The search radius should span the entire zone
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Adjust the No lags; the Lag distance will change accordingly
5. Use a spherical model type.
6. Perform a preliminary vertical variogram analysis for the data values. 7. Repeat steps 1-6 for every zone in the model.
8. Check the value of the Vertical range and compare with the cell thickness for every analysed zone by checking the Average zinc (along pillar) in the Statistics tab of the zones.
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Use raw log data as source
Toggle off Simbox mode for vertical analysis
Grid layering should be ½ of vertical range
In this example, the vertical range can be interpreted as 26,516 (project units) from the variogram. variogram. Half of the vertical range in this example amounts to 13 (project units). This suggests that grid layering should not exceed 13 in thickness. In the statistics tab, t he current grid layer resolution is 12,6 w hich is correct.
