by Brenton Crawford, Chief Geoscientist at Datarock
Drill core photography has traditionally been obtained almost exclusively for record-keeping and, therefore, not seen as a valuable dataset. Due to this, relatively low importance has been placed on acquisition workflows, leading to variable quality and consistency.
However, recent advances in modern analytics and technology have enabled the extraction of considerable value from drill core photography. In general, the better and more consistent the imagery, the better the results.
In view of this, Datarock has devised the following best practice guidelines to maximize the value of drill core photography in a way that is relatively low cost and straightforward to implement.
Timing of photography
The timing of core photography, relative to other steps in the core processing workflow, will affect the downstream analytics.
- If geotechnical or textural analysis is required, the core should be imaged as early as possible (even at the drill). Modifying the core (through transport or human annotation) should be minimized.
- If sampling and geological observations need recording, the core should be photographed when the markup is complete.
- We do not recommend photographing the core after it has been cut unless there is an earlier photo.
It is becoming more common to take multiple photographs of core trays as they are processed. A typical workflow might include:
- At the drill rig: an early photograph immediately after drilling;
- After drawing meter marks and measuring core loss: this is the preferred stage as Datarock processing can assist logging;
- After logging: photography after logging and markup;
- Final: a final photograph after cutting and sampling.
This sequence provides a comprehensive record of the core processing workflow, the best-case scenario for analytics, and an audit trail of any changes or damage to the core in transit.
Preparing core trays for photography
We recommend several core tray preparation steps to maximize the potential benefit of automated extraction of information from core photography.
Writing on the core tray
Certain information should always be written on the core trays, preferably in a consistent location and format:
- To and From depths, preferably in the top left for the ‘to’, and bottom right for the ‘from’ value. This speeds up adding metadata later, either manually or through optical character recognition (OCR);
- Drill hole name—consistent with no underscores;
- Core tray number—001 format;
- The word ‘START’ written on the top side of the tray in a consistent location—this will later aid in programmatically identifying photos taken upside down or rotated.
Writing on core
Writing on the core is best completed with permanent markers, wax markers, or chinagraph pencils, as they are the most durable and do not wash off when undertaking wet photography.
Writing can generally be divided into three categories:
- Meter marks should be written in white or black (depending on core color), with large, clear writing. The sample line should always be to the left of the numbers and extend from the top to the bottom of the core. This will help minimize the optical character recognition confusing it with a ‘1’.
- Sample marks should be written in red and will be differentiated from meter marks based on color. The numbers will be written in the same format as meter marks.
- Lithological boundaries should be marked in yellow. Lithological metadata should be written on the left-hand side of the boundary, and depth information on the right.
In general, additional writing on the core should be minimized as it obscures the rock texture. If required, use distinct colors, which will not be confused with the three categories listed above, and consider taking an additional photo after meter marks have been drawn on and prior to sampling and lithology markings.
Orientation lines
Orientation lines should be aligned with the bottom of the tray channel but still visible to the camera. Ideally, this line will be marked with a permanent marker, wax marker, or chinagraph. Importantly, this marking should remain consistent to allow automated processes to work accurately. The base of the channel is preferred as it allows the orientation line to be imaged but doesn’t obscure the rock texture.
Joints
Joints should be aligned but opened slightly (~0.5 cm / 0.2 in) to allow the edges of the fractures to be clearly imaged by the camera.
Drillers’ breaks
Drillers’ breaks should be marked on the core with a visible cross (‘X’) within 5 cm (1.97 in) of a mechanical break, including at the end of a row if it is a mechanical break.
The color can change depending on the rock’s color (with red as the default), but the crosses must be clear and visible to the camera. When multiple mechanical breaks occur close together, pairs should be marked closer together to aid the algorithm in attaching them to the correct break.
Use of color bar and scale card in photographs
Variations in lighting can be corrected using a consistent color bar. We recommend the ‘Calibrite ColorChecker Classic’, which is available from multiple suppliers. It is suitable to place within the frame or can be cut and placed in a long strip along the edge of the core tray.
Scale cards should also be used when measurements from images are required. We also recommend including a header sheet to provide a standardized format and a prompt for personnel to include tray data.
Photo acquisition
While many proprietary core imaging systems that take high-quality photos are coming to market, there are still some relatively simple and inexpensive steps to significantly improve the quality and consistency of core photos.
The following sections provide suggestions to the various aspects of core photo acquisition.
Lighting source
The type of light used to illuminate the core tray will play a significant role in the quality of the image. This applies to general core shed lighting and controlled-source lighting within a photography system.
A key metric to understand when choosing a lighting type is the Color Rendering Index (CRI). CRI is an attribute of the light source. It is a quantitative measure of its ability to reveal the colors of various objects faithfully in comparison with an ideal or natural light source. Light sources with the highest possible CRI should be used.
We recommend using lighting with a CRI measurement of at least 80. These are generally inexpensive, modular, and remain relatively low-temperature compared to incandescent lighting sources. Your electrical supplier will be able to readily source high-CRI lights.
| Light source | Typical CRI value |
| Fluorescent lights | 60-80 |
| LED (standard) | 70-80 |
| LED (high CRI) | 80-95 |
| Incandescent light bulbs (2700K) | 100 |
Light diffusers
Intense point source lights can cause reflections on the drill core, especially if it is wet. Light sources (preferably high CRI) should be diffused using an opaque shroud and, ideally, should not be located directly above the core tray. It is best to avoid positioning light sources behind the camera, keeping them off at an angle or to the side of the center of the tray, as this will reduce the reflections commonly encountered in wet core photography. Reflections on core can mask important geological features and can also be confused with core markups such as ori and cut lines.
Cost-effective camera solutions on the market such as the Casper system utilize core shed lighting and use a diffuser to minimize glare.
Removing non-controlled light sources
The next lighting control step is to remove non-controlled light sources to ensure consistency. We recommend an indoor environment and blockout shroud to remove all background lighting. Thus, outside light (often fluorescent) from the core shed or sun can be completely removed and replaced with a controlled light source inside the system. These products must not induce reflections on the core. Some relatively simple options are the roller rack and the floor frame.
Camera position
The camera should be positioned directly over the core tray to ensure all the core is included in the image. If it is taken from a high-aspect ratio, or if multiple trays are captured in one image, the tray can obscure the sides of the core.
Polarized lens
When the core is photographed wet, it can be challenging to avoid reflections. A potential way to remove these is by using a polarizing lens. However, these lenses can reduce the amount of light reaching the sensor, meaning more powerful lighting sources are required.
Resolution
It is important to take photos at a high-enough resolution that captures sufficient detail for current and future use cases. It is good practice to aim for around 100-micron resolution for core photographs.
Modern, full-frame DSLR cameras generally have between 30 and 50 megapixels. Single-shot systems positioned approximately 1–1.5 m (3.3–4.9 ft) above the core tray will produce images with approximately 100–150-micron resolution.
It is possible to position the camera closer to the core tray and take several photographs that are then stitched together. However, this can be challenging and often leads to distortion and artefacts in the stitched image. We don’t recommend this approach as these drawbacks often outweigh the benefits.
Whatever camera is being used, it should always be set to capture its maximum image quality.
Focal length / Zoom
The camera should be held in a fixed position to the core tray and the lens’s focal length, or zoom, should generally also be fixed.
Aperture / Depth of field
Sometimes aperture adjustments are required when switching from full core to half core. These settings should be recorded and changed when required. However, the recommended settings below should be suitable for the common range of imagery.
Focus
Use autofocus or fix the focus for every image to minimize blurriness.
Recommended camera settings
Unfortunately, no set of camera settings can work best for all rock types. Very dark rocks can require different settings to very light rocks, and as with most things, there are trade-offs to be made with some settings. Get in touch for advice on best practice camera setups for your situation.
Fully manual settings will yield the best results but will take some experimentation depending on the rocks, lighting conditions, as well as the exact camera and lens being used.
Image extent
The photography system should be set up to capture the entire core tray on all sides, with one tray per image.
Do not cut out any of the tray as it often contains data such as depths and it can present problems to the various machine learning models.
In general, a higher-quality image further away will be of more value than a close, low-quality image, particularly with bad stitching.
Photograph naming convention: Image metadata
To ensure images are uploaded to the platform and ingested correctly, the metadata must be recorded consistently according to the standards listed below. Critically, From and To depths for each core tray should be recorded in the file names of each image.
File names are to be delimited by underscores ‘_’, containing information on hole ID, tray number(s), the From and To depth at the start and end of the tray, and whether the hole is wet or dry.
The minimal metadata recommended is: HoleID_TrayNumber_FromDepth_ToDepth
Example: DDH1_001_5.00_10.65
Should a photo contain two core trays, a ‘+’ will be used to note this. The recorded depths should cover both trays (i.e. the start of the first tray and the end of the second).
Example: DDH1_01+02_5.00_15.00
To note whether a photo was taken wet or dry a _W/D can be added.
Example: DDH1_01+02_5.00_15.00_W
It is preferable that this metadata is collected during the photography process and entered into a simple application. Most modern DSLR cameras can sync to third party applications. Please speak to us if you require assistance in creating a custom application to record the photography metadata.
To find the cheat sheet for core image optimization, click here
For more information: Get in touch with Brenton on LinkedIn, or visit datarock.com.au
