By Sam Bain
A standard workflow in Leapfrog is building a geological model from the interval columns of imported drillholes. This workflow requires the importation of a collar locations file, a survey file with drillhole geometry, and an interval table with the observed lithological contacts. In addition, other down-hole information such as from geophysical logging or drill core assays can be imported as interval tables.
Often there will be problems with the drillhole data. Perhaps the logging in the field was inaccurate and two unique units were incorrectly lumped into one. Of course, the opposite could happen if an eager geo sub-divides a single sandstone deposit into separate poorly sorted and well sorted units. In these situations, the drillhole data needs to be edited so that a new unit is defined or existing units are combined. The “Group Lithologies” and “Split Lithologies” tools in Leapfrog allow you to create a new interval column based on edits of an existing interval column. An additional tool called “Interval Selection” has been developed that uses elements of the grouping and splitting workflows to create a new interval column. In this post we will look at the “Group Lithologies” tool.
How to create a new grouped lithologies column
Once a set of drillhole data has been imported, right clicking a lithology interval table in the project tree will display the range of options available (Figure 1).
The first of these is the “Group Lithology” option. Selecting this option will open the first grouping dialog (Figure 2).
The “Base Column” option is the interval column you wish to group. This would typically be the geology/lithology column. This is the option shown in Figure 2 above. However, groups may be based on a user defined split lithology which can be selected from the drop down menu. It is important to choose an informative name that will clearly identify the data on which the group is based, and any other helpful information such as the user who created it and perhaps the date. This will help other people looking at or working with the project, as they know who to talk to about specific data interpretations.
Once a base column and name have been chosen, the group editing dialog will open (Figure 3). This dialog is divided into two windows. The window on the left initially contains the lithologies as defined in the chosen base column. The empty window on the right will eventually contain the groups you define.
When the grouping dialog first opens, the drillholes are added to the scene (Figure 4). The colouring reflects the lithologies in the base column. The visibility of these lithologies can be toggled on and off by clicking the eye symbol beside each lithology in the grouping dialog.
There are two options for grouping lithologies – manual selection or auto-grouping. Manual selection requires the user to pick the lithologies from the original lithology column and place them in new groups. Figure 5 below shows two new groups and their constituent lithologies on the right, and two remaining ungrouped lithologies on the left. This is the stage where each new group is named.
Groups can also be created by using the ”Auto Group” function. This has three options for automatically processing the existing lithology codes to make new groups. As many lithologies are named based on an in-house alphanumeric code, Leapfrog includes the option to create new groups based on shared letters and numbers at the front or back of a lithology name. In Figure 6, groups will be created based on the first letter of each lithology name.
This option will group Alluvium with Aquifer Miocene Alluvium and Glacial Till with Gravel (Figure 7). Names are automatically assigned to each group based on the letter by which the group was defined.
Should each existing lithology need to be assigned to a separate group, there is a third option which automatically performs this workflow. In this case, each group will have the same name as the lithology it is based on (Figure 8).
As new groups are created, the new grouped lithologies will be displayed on drillholes in the scene. If required, the drillholes can be changed back to displaying the original lithologies by using the drop down list on the interval table in the scene list (red square in Figure 9).
Once you are happy with the grouping, clicking the “OK” button will close the dialog box and save the current groups. Groups can be edited at any stage by double clicking the appropriate object in the project tree. The new groups can be used in exactly the same way as un-grouped lithologies when making a new geological model. The contacts between grouped lithologies can be used as contact points to create new geological surfaces.
Grouping can be used for a range of reasons. In some cases a broad geological model may be required. This might entail grouping basement units into one group, intrusive units into another group, and sedimentary cover sequence units into a third group. While these groups can be used to create a model showing the general structure of the area, the original lithologies are retained and can be used to create a more detailed geological model.