Seismic Studio Tutorial - Part 4

“Stack QC”

Boulder, Colorado USA

November, 2004

Overview

Stack slice QC generates arbitrary 2D lines, called “slices” from your 3D prospect. You specify the CMP spacing and grab radius for each line. Traces can therefore be multiply assigned to CMP’s. This can take some time.You pick a velocity field using semblance analysis for each stack. This velocity field is “throw-away”; it does not get exported.You create stacks and can look at any two stacks from the current slice.The traces you stack are the actual un-decon’d data you use for your refraction picking.

Stack QC Window

Accessed under Stacks on the Menu Bar

The Stack Slice window provides a wide range of functionality:

•Slice selection along any arbitrary line •Semblance velocity analysis •Stack with and without statics•Azimuthal limitation

Stack Slice Window

Works from slices you select from your data

Is map-drivenDrag a line on the map to create a slice

Set a CMP spacing and capture radius

Creates a 2D SEG-Y file for each slice

Slice ManagerDelete old slices

Select current slice from list

Control Pane 2This contains the map and map controls

Control Pane 1You drive the window from

here

Trace and Semblance

Display PaneThis is where

you see everything

Control Pane 1

Stack display – provides control over stack trace display parameters: wiggle, fill color, trace excursion, etc.Stack filter – for applying simple bandpass filter and some gain optionsSalience – experimental – let’s not go thereAuto picker – experimental – we are developing some automatic velocity picking functionalityAzimuth – for azimuthally limiting traces in the semblance analysis and in the stack. Semblance/Mute – for setting min/max velocities in the semblance and the stretch mute percentage

(** Bold italics indicate important, often used tabs.)

Control Pane 1

Slice Manager – this is where you select which slice you want to work on

Statics – for applying static corrections

Gather filter – for applying a bandpass filter and gain options

Stack manager – this is where you actually name your stacks and generate them

Gather display – provides control over stack trace display parameters: wiggle, fill color, trace excursion, etc.

Change map to any value in database

Resize bars – click and drag

Here we have gone to the Slice manager and see a slice we created back in Feb, 2004.

We have pulled up the resize bar to make the base map bigger. The black line shows the

existing slice.

To create a new slice simply click and drag a line across the map.

You will see this dialog for creating a new 2D SEGY file.

Then you see this information dialog.

This dialog comes up. There are two passes. The first pass counts. Then space is allocated. The second pass

creates the actual SEG-Y file. The second pass can take a while for long lines with

wide trace radii.

Select the line in the Slice manager, the line is highlighted in red on the

map.

Click on these navigation buttons to move into the line.

Once you see a CMP gather you like, you can pick velocities.

As you move your mouse across the gather, the green line on the base

map indicates the shot/receiver line

for each trace.

Left click to set velocity points.

Click “D” to delete the

closest point to the mouse.

Click on Velocity display and push the Recompute velocity field from knees

button.

Now you can “drive” the velocity analysis from this display. Left-click where you want to pick a new

velocity point.

Go back to the Velocity display and click the Recompute button again.

Break time

So, at this point we have:Created a slice

Computed a velocity field.

But our data have no statics applied, we will do that later. First, let’s create a stack with no statics applied.

First, resize Control Pane 1 so you can see more controls.

Second, click on the Stack manager tab

1. Type in the name for your stack.

2. Type in the maximum time for your stack. The default is 1000

msec.

3. Click on Create new stack button

To see your stack, click on the View two stacks

tab.

Then click on the stack name in the drop down list, and click Load.

Applying statics

Now we will create a stack with statics applied.

Click on the Statics tab

Click on the Apply statics from the selected header radio button.

The default header location is Static Correction which is where your current

refraction statics are stored.

Recompute stacking velocities

Now you should repick your velocities, because they after refraction statics are applied they will change.

We recommend repicking the velocities at the previous

locations.

The best way to do this is to zoom in (right mouse button) on a previous location then

left click.

Click carefully on one of the dots

This one doesn’t need much change.

This one should be changed, especially under 700 msec.

Recompute the velocity field

Create a new stack – don’t forget to name it

Now you have two stacks … and they zoom together.

Conclusions

Slice stack QC is for checking the quality of your statics solution.You can create as many stacks as you want. The window only keeps one velocity field at a time. You cannot save a velocity field to retrieve it later.You cannot export a velocity field to another processing system.