Gridding seismic interpretation with faults
Abstract
Case: A set of seismic lines for a certain horizon has been interpreted in Kingdom Suite. Also fault line traces are interpreted. The lines are read into a Geocap project.
Purpose: The data will be analyzed and edited to make them suitable for gridding in Geocap. The documentation will describe errors and inconsistencies in the data and how to clean and edit the lines in order to get a good gridding result.
On this page:
Triassic demo project
A demo project called Triassic demo was created with the initial seismic lines and faults. The picture below shows the project and the initial interpreted lines and faults from Kingdom.
The text follows closely what happened during the work.
Disclaimer
Due to a substantial amount of errors in the seismic lines and fault traces, a large part of this case study deals with correcting the errors. The way it is corrected is in principle simple, but requires an suitable knowledge of Geocap functionality which consequently is presented during the text.
Having corrected the errors on the input datasets, the gridding is straightforward and explained in detail by menu images. Geocap has a unique fault gridding algorithm for incorporating fault traces into the result grid surface.
If needed, there is also an option that Geocap personnel can assist in practical work if necessary when a similar project has to be performed.
Seismic lines and faults displayed in Geocap, but interpreted in Kingdom
Error in seismic lines
Analyzing the seismic lines closer it reveals spikes. In the table view one sees the z-values for the spike points are -999. An error has been introduced somewhere in the process of saving or importing the data. No matter what the reason is the spikes must be removed. The easiest way is to mak the dataset active and eliminate the spikes with a shell command:
- Interpreted_lines->Make Active (will transfer the lines into active data)
- In the shell: eli lt 0 ; # eliminate z values lower than 0.
- Interpreted_lines->Assign Data From ...->active (will transfer the lines back into the project)
- The input also showed three very long lines with just start and end points. These line were deleted using:
- mak cel dis 30000 ; # make a new cell if distance between points are greater than 30000.
- The lines were then assigned back to the project.
The interpreted lines are now cleaned and updated.
Seismic lines before and after eliminating spikes
Error in faults
Deleting fault throw boxes
There are two ways of deleting the boxes:
1. The first way to delete the fault throw boxes is simply to delete them interactively:
Faults_from_Kingdom->Edit points and lines - Delete - Repetitively - Delete all points in a cell - Start delete. Stop delete.
This method is applicable when the fault throw boxes are separate cells (as in this case). If the fault throw boxes are part of the fault traces (which often is the case) one has to delete the individual points.
2. The other way to delete the fault throw boxes is to use a shell command for quick removal of points. The first observation is that the fault throw boxes are separate cells and each cell has four points. If no fault traces has four or less points one can delete all cells containing points lower than five.
Gridding of seismic lines and fault traces
Conclusion
The text in this documentation shows the principles of data cleaning using command objects and some smart shell commands to do effective work. The use of shell commands is an option and is meant for direct action and shortcut in some cases. There is normally an equivalent in a command object using a menu. In this text a few shell commands are presented to show their use.
Gridding of interpretation lines and faults requires input data of high quality. The fault traces should be properly closed with no fault throw boxes. It is a necessity to master the editing of input data to get it all correct before gridding.