· Assigning templates to a project
· Image processing
· Logging in the core shed
· Segments, core blocks and spacers
· Structures and lithology contacts
· Exporting data
In my last article, I showed you how to set up a data collection template, basically a logging sheet. In this article I will show you how to use the template, together with calibrated core tray photographs, for digital logging in the core shed.
Assigning templates to a project
As in Figure 1 we simply open our project, go to Project -> Settings and assign the structure and the lithology templates for the project.
Full instructions are included in the help manual, but before we start logging we need to have undistorted images of the core trays we want to log at our disposal. There is not a lot of preliminary work that needs to be done on these before we can start logging. Basically we simply need to add the images to the project, assign a frame to each of them, mark the reference points in the raw image, then undistort.
Logging in the core shed
Once you have a set of undistorted images, which doesn’t take long, your next step is to find the core trays that you want to log and start logging. You will need to have your laptop running StereoCore™ PhotoLog with you in the core shed.
In order to log the descriptors for a structure, select the structure marker tool in the toolbar and place the marker in the image (by holding down the Shift key and clicking in the image) close to the structure you want to describe.
You can see how the description box in the Structure Markers tab at the bottom of the Data Input screen opens up automatically so that you can start logging as soon as you have identified the structure that you want to log by placing the marker in the image. Logging a lithology contact works in exactly the same way, you just select the Lithology Marker instead.
One thing that you will notice when logging with structure or lithology markers is that depth and other automatic measurements are not reported. These measurements will be carried out using StereoCore™ PhotoLog later. In the core shed we want to maximise our logging efficiency and log as many structures as possible in the shortest space of time.
A brief digression to explain why we log this way. StereoCore™ PhotoLog uses calibrated images. We draw segment lines and mark core blocks in the images in order to provide a depth reference for structures and lithology contacts, which are also marked in the image. Drawing a structure results in automatic measurements of goniometer angles and structure depth. Similarly placing a lithology contact results in automatic measurement of its depth. However drawing all this stuff does take a fair amount of time, and in addition is not a skilled job – unlike logging descriptors. In order to maximise the geologist’s effectiveness on site, we postpone all of the stuff which is not actually necessary to do in the core shed.
Segments, core blocks and spacers
Once we’ve completed the descriptor logging, our next step is to put the “scaffolding” in place that allows us to make measurements of depths and angles from the images. As explained in the user manual, we first have to place the image dividers and the “blue line”, as well as set the core diameter and core offset of the image. These parameters allow us to reconstruct a three dimensional model of the core from the two dimensional image.
Having calibrated the image (i.e. placed the blue line etc.) we next draw our segment lines and place core blocks in the image, as shown below. Full details are in the user manual for this process. This is a job which can be done by a technician and cross-checked by the geologist, as it’s very mechanical. In brief, for segments, segment lines need to be drawn over the reference line and the core edges need to be fitted appropriately. Core blocks need to be placed at the correct point in the image and the depth filled in as written on the actual core block.
Structures and lithology contacts
The final step of the logging is to draw the structures and lithology contacts on the image, allowing us to measure their depths and associated angles. Once we have done that we associate the data we logged earlier with the structure or lithology contact we have just measured by simply dragging and dropping.
Placing a lithology contact and dragging and dropping the associated lithology marker works in exactly the same way.
Once the logging is complete (or at any stage), the logged data can be exported in Excel format.
The logged structures, with their depths and alpha and beta angles, will be found in the Structure Log page of the Excel file. Similarly the Lithology log contains the details of the logged lithology contacts.
Incidentally, if we import a path survey for the borehole, we can output the dip and azimuth of the structures. I will explain how to do that in a separate article.