...
To display a smaller part of the surveys one can use the CO under Utilities->Display stacking velocities in line mode. Set always the correct attribute (scalar or velocity if field data) and select for example Eliminate outside cursor: A small part of the dataset around the cursor is selected for display and also saved in workspace as elioutcursor. Similar for an area zoomed into when in 2d mode and part of dataset can be saved as workdata in workspace.
...
Cube gridding from stacking velocities
The command menu Cube gridding from stacking velocities are gridded into a time-velocity cube that will be used for depth conversion. Read more about this theme in Gridding of time-velocity cube. can be activated for data with schema Stacking Velocities. Stacking velocities have the format: x y two_way_time velocity. Two_way_time is used because time is recorded after having traveled down to the reflector and up again.
Initially, set the correct attribute to tell whether stacking velocities are in scalar or field data velocities or have some other name. Press Set when the correct attribute selection is done.
The cube gridding command menu allows the user to set a proper origin, set the cube increments, use Adjust (gridding window) to Increments to align the cube at increment values. Be sure to set the gridding window correct before gridding. Pressing Window Frame will display the coordinates written in the grid window as a frame. Also check the zmin zmax values to see that the vertical extent is correct. When the increments of the cube are correct hit Calculate to get the number of rows, columns and layers in the cube.
Before gridding some options in the grid option page should be set or checked.
The grid option page allows for selecting an outline (or reference line) to determine where the gridding will take place. This is superior to the automatic method.
The Result cube page allows for saving the cube into a folder. A copy is also saved as in workspace as cubegrid. The cube dataset is given the schema Cube. Thus the cube will have many relevant commands visible for further actions.
Testing cube gridding
The Test page in the gridding menu allows for testing the gridding at various cube planes to check the gridding parameters and study the quality of the input. This is done as shown in the display below.
Testing cube gridding using a manipilator plane
After testing the gridding at a few planes and securing all parameters are properly set, the overall gridding of the stacking velocities into a velocity cube can take place. The resulting cube can then be visualized with various display techniques.
Updating the cube with checkshot data
In many cases there are also control data for the velocity cube available in form of checkshot wells. These well data should have the format: x y depth one_way_time. They can be used to update and correlate the velocity cube so that the layers will match the checkshot wells. Use the command menu Utilities->Updating velocity cube to checkshots.
The Set update filter option is available for excluding wells that obviously has wrong starting velocities, namely the sound velocity in water.
Checkshot wells organized in a folder
Sometimes the checkshot wells must be generated by merging velocity and time from one dataset into the well position of another dataset. That is done by the command object Merge x y with two data parameters found under schema type Line folder utilities. Set your folder with well positions to that schema type, or copy the command object from the repository into Item Commands on that folder. Then one can generate the proper checkshot wells from separate well data information.
When reading the checkshot wells into the algorithm, all wells are collected into one dataset. This dataset is also transformed into x y two_way_time velocity so it will match the velocity cube. All checkshot wells are prolonged to go from cube_min to cube_max in order to produce matching data all along the well string. The transformed and prolonged checkshot wells are saved in workspace data as updatedwells and can be further inspected.
The default updating algorithm is called Moving average which means that the differences from the checkshot slice and cube slice are gridded with a moving average interpolator and added to the cube slice.
The Tensor algorithm uses a bell shaped b-spline tensor for updating and is recommended for a local updating around well. A counter for each layer is listed on the terminal window during updating.
After updating the cube with checkshot wells the cube should be displayed and checked that the cube layers are matching the well data.
Transformed checkshot wells with bottom layer before and after updating cube
The above figure shows that the cube matches according to the color code of the checkshot wells by displaying the bottom layer before updating the cube (to the left) and after updating the cube (to the right). After smoothing and updating the velocity cube it can now be used for depth conversion.
Checking the cube visually
| Section | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
| Section | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
Depth conversion using a dedicated command object
...