From mining and mineral exploration to engineering and construction, companies in an array of industries make key decisions based on the results of core sampling. This means that the quality of the samples is vital, but so is, more often than not, the speed with which they can be reached, retrieved and analysed.
In fact, the operational costs of keeping drilling rigs and staff on site mean that every extra minute waiting for the core analysis, which can determine whether to keep drilling or move location, adds extra costs to the project's balance sheet. Hence, getting it right from the beginning is essential.
The first step to doing so is ensuring that the right equipment is brought to the site and that the staff knows how to use it. Chris Drenth, engineering director for performance tooling at Boart Longyear, explains: "In order to ensure consistent and cost-efficient recovery, start by avoiding costly failures and lost productivity due to malfunctions, overloads, or simply insufficient capabilities.
"Operational challenges can be overcome by considering the whole plan, expected formations, and water table, in order to secure the most reliable equipment, drill string, wireline tooling, and bits available, and the drilling system with the most effective feature sets.
"Having properly addressed drilling equipment and drilling systems, ensuring that the drilling crew employs ‘best practices' and optimal drilling methods can be a significant challenge. A significant impact can be made by simply refreshing a drill crews understanding of the fundamental drilling relationships between rotational speed, bit weight, bit torque, and fluid flow, and how to target bit life versus penetration versus bit sharpening."
Rune Lindhjem, product manager at Devico, a developer and supplier of directional core drilling technology and services, agrees that planning and considering different technologies are key to success. "To get the most out of directional coring technology it is important to plan in advance and have a clear understanding of the benefits and potential limitations. Proper planning makes it possible to determine what the best approach may be to fully delineate an ore zone in the most time- and cost-efficient way.
"There are many factors, like depth, grid, ore shape, topography, number of rigs, etc. that determine whether it may be more efficient with few mother holes and many side tracks or the opposite, performing long or short corrections, starting with a flatter or steeper angle, etc."
Consequently, to ensure the highest value for their client, service providers often need to work closely with geologists to analyse the drilling program and determine the most efficient tools for the job.
Faster going down
When it comes to maximising penetration rates while minimising costs in core drilling the choice of bit is essential and suppliers offer a wide variety of high-quality diamond bits based on different technologies.
In the second half of 2017, Boart Longyear launched a new patented core bit - the Longyear coloured-series diamond bits. The patented technology allows the bit matrix to chemically bond directly to the diamonds, improving diamond retention and performance across a wider range of formations. However, one thing to keep in mind is that choosing the bit with the maximum penetration rate might not always be the best choice, says Drenth. "For maximum overall efficiency, consider selecting bits that minimize replacements (trips of the drill string to change the bit) as opposed to maximum penetration rates, or vice versa, depending on the project. For example, at shallow hole depths, choosing higher penetration rates versus longer bit life can be more productive overall. Conversely, at greater depths choosing longer bit life over penetration rates is more productive as it reduces the frequency of rod string trips."
Consequently, depending on the frequency of rod string trips, the rods can be as decisive in determining the speed of the core retrieval process as the penetration rate of the bit. Internal upsets can reduce weight and extend the pullback and torque - or the rig's available power for other demanding applications - while also reducing operator fatigue if handled manually. When drilling deep holes, this translates into greater depth capability on any rig, explains Drenth. "Also, inner tubes will trip in and out of the rod string up to 50 per cent faster, which means more time can be spent actually cutting core with ‘bit on bottom'."
For maximum productivity, Boart Longyear recently launched the XQ rods. The rod's automatic thread starts eliminates the need for the helper to apply a back-turn to start each thread while tripping the rod string for bit changes. "The benefits of any level of automated rod thread make-up are otherwise quickly lost with each stuck thread. Similarly, to maximize bit cutting time, consider that Boart Longyear's XQ W-Wall rods provide up to 50 per cent faster tube tripping," Drenth adds.
Speeding up recovery
When deeper exploration drilling is needed, using directional drilling technologies to reduce drilling metres can be the best option. With directional drilling, multiple targets, or target zones, may be reached from a single drill hole and drill pad by changing the direction of the hole or side-tracking it to create a new hole. Besides, deeper ore zones may often have a shape and form that can cause steep or unfavourable intersection angles when drilling straight holes. With directional drilling technology, this can be avoided by drilling the initial part of the hole at a steep angle and then curve it into an angle more perpendicular to the ore zone.
Lindhjem explains: "By altering the direction of the hole, the hole may be guided through one target zone before it is directed on to another, making it possible to intersect multiple target zones with just one hole. Sidetracking, on the other hand, creates a new hole part way down a previously drilled hole [the mother hole]. This new hole may be steered away from the old using directional drilling, giving the opportunity to intersect a target zone at multiple locations or in a fixed grid. Both these approaches make it possible to delineate an ore body with significantly less drilling and higher accuracy compared to starting each new hole from the surface."
Devico's proprietary DeviDrill directional core barrel is designed to fit and operate in a similar fashion as a standard wireline core barrel and may be operated by most drill rigs capable of wireline core drilling. "Compared to other directional drilling technologies, like mud motors or wedges, the DeviDrill is unique in the sense that no additional or special equipment is required on site, and that longer directional changes can be performed continuously without retrieving the core barrel from the hole. With the DeviDrill a core sample will also be collected and retrieved during the directional drilling process, using the same system found in a standard wireline core barrel," explains Lindhjem.
Faster going up
Once the drill has safely reached its target, securely retrieving the core becomes the main priority. Selecting a standard Q wireline tooling size can ensure a smooth and fast retrieval and avoid the core getting compromised or stuck while also ensuring minimum fluid resistance when flushing out cuttings, says Drenth. "Boart Longyear offers QTK systems for an increased core size while maintaining inner tube wall thickness, but avoid using ‘thin wall' systems, which have restricted fluid passages and significantly reduced inner tube wall thickness with up to 30 per cent less resistance to sample expansion or wedging of angular core segments."
Furthermore, selecting chrome-plated inner tubes not only extends wear life but also eliminates the internal wear ridges that can form on non-plated inner tubes, which can snag the edges of core segments and cause core blocks or jams.
The quest for speed does not stop when the core is safely out of the ground; logging and analysing the properties of the core quickly can be vital to making timely and accurate decisions.
One way of speeding up the process when the core is out of the ground is with an onsite logging device such as Imdex's Reflex IQ-Logger, which has just been integrated with Micromine's suite of Geobank products. The Imdex Reflex IQ-Logger is a handheld structural logging device, which can be simply rolled along the orientation line on a diamond core. The device automatically records depth and structural measurements at the press of a button. The integration with Micromine's suite of Geobank products means that measurements are automatically logged within Geobank allowing users to analyse their logging data in near real-time even in areas with poor connectivity. The Imdex solution significantly reduces the time required for logging and the digital transfer of structural measurements provides a reliable audit trail. In-built data verification capabilities and Stereonet projections also ensure orientations are accurate and reliable.
"The seamless integration of Reflex IQ-Logger data collection with the logging workflow within Geobank Mobile will benefit clients - providing them with accurate geological data on-site, in near real-time, to make timely decisions," says Michelle Carey, Imdex's general manager - product development.