Seismic – Domain ConversionObjectives

• Quality control time/depth relationships for wells• Define velocity model intervals• Create an uncorrected velocity model using well data• Create a final corrected velocity model using well data• Create a velocity model with uncertainty• Depth convert a 3D Grid• General depth conversion

Optional:• Create a velocity model using a seismic velocity cube• Create velocity model using stacking velocities (xytv point-data)

Overview

• ‘Velocity Modeling’ is separate from ‘Domain Conversion’• Interactively switch between time and depth for converted

objects• Define the velocity model by:

- Surfaces/constants

- Well Time/Depth Relation

- Velocity Cubes

- 3D grids• Convert both ways with the same model• Convert objects independent of the 3D grid• Perform conversions in the process manager

Velocity model – bridges the gap between time and depth domain

Time domain Depth domain

Velocity model

Time -> depth conversion

Depth -> time conversion

The Workflow

• Define velocity model1. Define velocity intervals (usually between time

interpretation surfaces)2. Define velocity functions (automatically calculated or user-

defined)3. Define output (e.g. velocity cubes, V0 and k for Q.C.

purposes)

• Domain convert via1. Right click on object (uses currently ”active” velocity

model)2. General Depth Conversion Process for Multiple objects3. 3D Grid Conversion4. Within a workflow in Process manager

The Process

Velocity

Corrections

ZONES

Output

Advanced

Datum

Datum

VoVo + kz

Vo + k(z-z0)

A: Auto 1. Correction (Vo) 2. TDR (Vo & k)B: User 1. Constant 2. SurfaceC: Velocity SEGY (average)D: 3D Velocity Property (average)

Datum

VoVo + kz

Vo + k(z-z0)

1. Seg-Y 2. Velocity Surfaces 3. Well Data Points4. T & V logs 5. Residual Points 6. Output Sheet

1. Constant 2. Surface3. Horizon*4. Well Tops

1. Constant 2. Surface3. Horizon*

Or none

1. Well trace Md inc 2. Depth & Time tolerance3. Velocity & k clipping

Additional Settings ++(Gridding & SegY settings)

Saved in Model tab

The exercise examples

Time/Depth relationship in wells Velocity Cube (SEG-Y) Stacking Velocities (Point data)

Velocity Model 1 Velocity Model 2* Velocity Model 3*

Active (selected) Velocity Model

Domain Conversion of objects*Optional exercises, see Attachments

Define intervals

1. In the Process pane, open the Geophysics folder and double-click on the Make Velocity Model2. Click the ”Append item in the table” icon as many times as available input objects3. Change Bottom Interval to desired type4. Select the levels to model, from Input or Models tab, click on its name and drop it into the dialog

box using the drop in arrow 5. Keep the Correction set to None

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Velocity modeling using well data

1. Select type of velocity model for each interval. When using the Linvel function for modelling, constants, surfaces or Well TDR can be used as input

2. Set V0 to Well TDR – Surface/ Constant3. Set k to Well TDR – Surface/ Constant

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Velocity modeling - Output

1. Open the Output tab2. Click on the data types needed as output

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5. Defines Gridding algorithms for Surfaces and resolution for Cubes, Surfaces and Logs.

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1. Open the Advanced tab.2. Check that ’Well velocity’ tab is open.3. Possible to set MD increment, depth

and time tolerance and clipping parameters for V0 and k. 4. Activate ’Output settings’ tab

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Velocity modeling – Advanced settings

Velocity modeling using well data

1. Open Settings for Wells and go to the Time tab. Select Checkshots, Well Tops or corrected sonic logs as source for time/depth (move the prefered source to the top)

2. Keep the parameters for the velocity model the same as the values shown3. Click Apply or OK to generate the velocity model

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Velocity modeling with uncertainty

1. Create a new velocity model with Well tops correction, based on the previous velocity model 2. Toggle on Activate uncertainty page icon to insert a Std Dev column under the Velocity model tab

and to activate the Uncertainty tab. Fill in appropriate Std Dev. numbers 3. Go to the Uncertainty tab and fill in appropriate Variogram parameters. Toggle on Iconize uncertainty

error surface. Click Apply4. A velocity model containing velocity surfaces with uncertainty built into them is generated5. Check uncertainty statistics and display the corresponding deterministic and stochastic V0-surfaces

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Deterministic

V0-surface

Stochastic

V0-surface

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Depth convert a 3D grid

1. Make sure the correct 3D Model is active2. From the Process tab, under Structural Modeling, open Depth Convert 3D Grid3. Select the appropriate Velocity Model4. Alternatively change the pillar geometry types for faulted and non-faulted pillars before Applying5. A new 3D Model will appear in the Models tab, with the input 3D grid name and an extension [DC]

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Depth convert Seismic data

1. Make sure the correct Velocity Model is active (Bold name).2. Right click on the 3D volume and select ’Depth convert by active velocity model’.3. Alternatively, from the Process tab, under Geophysics, open the General Depth Conversion process.4. Click on the 3D volume name in the Input tab and drop it into the dialog box using the Append selected

item to the list icon. Click Apply.

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General depth conversion

1. Make sure the correct Velocity Model is active (bold text)2. From the Input pane, right click on the object to be depth converted and use Depth convert by

active velocity model 3. Clicking the + in front of the depth converted object shows the now available time and depth

domains for the object 4. The Time/depth settings can be changed in the top Toolbar. Alternate between TWT and TVD

while observing the effect in a 3D Window

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General depth conversion

5. Alternatively, or to depth convert several objects, open the General depth conversion process6. Select correct velocity model from the pull down menu7. Drop in the objects by clicking on their names in the Input pane and then on the Append

selected item icon in the process dialog8. The Time/depth settings can be changed in the top Toolbar. Alternate between TWT and TVD

while observing the effect in a 3D Window

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EXERCISE Domain Conversion