Using open-source GIS software to interpret the subsurface from drilling and surface data.
I often meet geologists who do not realise there is free and easy-to-use software available that can generate quality geological cross sections. Generally, most geos use a combination of expensive 3D modelling packages and graphic design software for their geological cross section requirements. They usually have to export blank drill traces and draw on them using an additional graphic design software. This is not only expensive but impractical and requires knowing how to use 2 types of software which can be a learning curve. [paragraph 1/9]
Well, thankfully due to open-source contributors, there are free tools out there that can do just as well when it comes to interpreting drilling data in 2D. The best one I have found so far is the geoscience plugin that works in QGIS (credit to Roland Hill who developed it). [2/9]
Unsurprisingly, the plugin requires you to input a collar point file, and downhole survey table. Okay… so that’s an easy enough start!. Go to geoscience plugin -> drilling -> desurvey holes. Once this is done, you can desurvey your drill holes and add the down hole data by going to geoscience plugin -> drilling -> downhole data. You can add numerical and categorical data, so long as it is in the right format, that is, the interval values are numbers and correspond to attributes. You can even add structural data, following the latest update. [3/9]
All this data is stored in a source geopackage file in the root folder of your QGIS project. It is these layers that will be used by the plugin to create sections. I would recommend that you symbolise these layers now, so all the snazzy styles you make will be assigned automatically to the layers you generate later. You are then ready to take your sharpest katana and cut slices along your drill lines. Just go to geoscience plugin -> section manager -> map canvas, and your katana will appear on your mouse cursor. You can choose the section width, which is really handy, especially if you want to include additional holes that are not in line. You can even draw a long section (although this is less practical since the result is a fixed 2D view). [4/9]
Your section is displayed in another part of the world, far away from your current project extent. It will consist of drill traces, collars, the different DH datasets you have loaded, and lines showing x, y, and z values for georeferencing. Hopefully having symbolised your data earlier, you are set for the visual experience. Take a minute to flick through the layers, make sure everything is looking okay, and grasp the picture for your interpretation. [5/9]
Now the part that all geos love… Drawing! Yes, QGIS is a good drawing tool. All you need to do now is to create some line and polygon layers with which to draw your geology. I prefer to work with pre-attributed data with dropdown lists, and with advanced digitisation tools like tracing. That way you can have a section ready in no time with consistent attributes. Oh, and don’t forget to smooth your shapes! Advanced digitisation is something I will cover in a later blog post. [6/9]
All that is left to do now is to edit your decoration lines, sort out your labelling, and put it all into a map layout. Then you have it! A quality interpretation of your drilling data solely with QGIS! Awesome! [7/9]
Of course, it’s not perfect… There are a couple of minor things which I think the plugin could really benefit from. Having the option to create longitudinal sections with multiple stepped views throughout the section width. Or being able to display numerical data as graph along the drill trace. [8/9]
Overall, I think this plugin is great. Of course, it does not replace proper modelling, but for everyday section requirements, it removes the unpractical aspect of having to use two types of software. It keeps it simple by working within a GIS environment, and what’s more, it really helps keeping the cost down. [9/9]
Anyway, that’s my view. I’d really appreciate any comments that you have. Let me know if there is anything that I’ve missed out or anything more that you’d like to know.
Note that I have not mentioned the new QGIS OpenLog plugin from Oslandia. This is because it is fairly new and I have not had the time to play with it yet. The alpha version is available and from what I have seen on the website, creating cross sections is going to become even easier!
Have fun sectioning!
Dimitri
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