by Aleksi Autti, CEO at Arctic Drilling Company Oy Ltd
Arctic Drilling Company Oy Ltd (ADC) has been the preferred drilling contractor of Boliden AB (Boliden), chosen to work on their projects both in Finland and Sweden since 2015. Over the past few years, we have brought along directional core drilling as an extra service for our customers. The introduction of this service has been made possible thanks to the cooperation of Aziwell AS (Aziwell) and their AZIDRILL N-B tool.
Boliden Kevitsa chose directional drilling to reach three targets in the Kevitsa mine area, in Northern Finland, which had a limited amount of appropriate drill sites. We were the first company to utilize directional core drilling there using Aziwell’s AZIDRILL. Boliden Kevitsa chose this method, as previously our teams have performed it successfully on other Boliden sites.
We began planning for the project during the summer of 2021. Drilling started in October 2021 and ended with all targets reached before Christmas. Eventually, one of the three holes was drilled to over 1200 m (3937 ft), another one reached 1100 m (3608 ft), while the third hit 1000 m (3280 ft).
The Aziwell directional drilling method
Through Aziwell’s method, the core is collected and oriented during the steering phase with the AZIDRILL that is B-size 36.4 mm (1.43 in) diameter. The curves are usually planned to turn 4-9 degrees every 30 m (98 ft). Steeper curves are possible, but increased stress and fatigue on the rods should be considered. With AZIDRILL, there are no limitations of depth or where to use the tool. The length of the directional core drilling phase is determined by branching depth and the distance between the mother hole and the target. All holes and targets are optimized independently to reach the best ratio between saved drilling meters and the duration of the directional core drilling.
The team
In order to make directional drilling operations with Aziwell possible, back in 2018, ADC formed our first dedicated team of directional core drilling specialists, which were sent to Aziwell’s maiden project in Colombia to practice directional drilling. The main idea was to create a team that can handle conventional diamond core drilling but can also use the AZIDRILL tools for directional core drilling. Achieving this goal meant that external teams or contractors would no longer be needed when a client wants to use directional core drilling.
As a result, presently our team consists of seven drillers, who have been trained to operate the AZIDRILL tool independently on-site. The team is led by our directional core drilling supervisor Kalle Säärelä, who has the most experience with this method within ADC.
The rest of the crew was formed by assistant drillers to help with the physical stress, as this is an omnipresent reality in surface diamond core drilling.
Aziwell has assisted us with our directional drilling projects since then and with the training of new candidates. In 2021 they helped us coordinate and complete the project in the Kevitsa mine area.
The rig
At ADC, we have always designed and built our own rigs from scratch, both underground and surface. We use a wide rubber track platform on all our surface rigs to enable independent mobility with wireless remote control for difficult terrain. On the Kevitsa project, the drill site was in the middle of the mine site, so it was easy to access, and the terrain did not cause any issues. This is not usually the case in Nordic countries.
Our rigs have solid walls and are covered by a hood to keep the working space warm and dry during the Nordic winter, which can bring a lot of snow, temperatures of −35°C (−22°F), and other extreme weather conditions. All ADC surface drills have the capacity to drill down to 2000 m (6560 ft) depths with NQ2; we even have a rig that can go to 3500 m (11 483 ft). In Kevitsa, we chose a K2 rig with a 2000 m (6560 ft) depth capacity.
We always use a rubber track-based container unit for transporting and storing all the rods, tools, drilling fluids and other equipment during the moves between drill sites.
Reaching the targets
We started by drilling and steering the mother hole with AZIDRILL to its target. Directional core drilling was used between 600 m (1968.5 ft) and 686 m (2251 ft) after which we switched back to conventional diamond core drilling and reached 945 m (3100 ft) depth. The first branch was done by wedging from 498 m (1634 ft) and after passing the wedge, steering towards the target began. We hit a broken rock formation at around 542 m (1778 ft) depth, which also blocked the inner tube. As a normal procedure, we took the inner tube up and as a precaution, lifted the rods about 20 cm (≈ 8 in) from the bottom. Then we sent another inner tube down and once locked, we immediately discovered that the water was not flowing through and the water pressure just kept rising, so we lifted the inner tube again to identify the issue. We tried to pull and rotate the rods, but they were stuck and were not moving at all. After several rescue attempts, we had to accept that we had lost that branch. We cut the rods above the core barrel and saved all the rods except the core barrel. We never found out what was the actual reason for the core barrel getting stuck, but we suspected that blasting two days earlier might have had some aftereffects, which caused hole collapsing in the broken rock formation. Fortunately, we had already steered the hole and could cut out from the branch bend at 524 m (1719 ft) and continue steering the hole towards the target as soon as a new branch was formed and cleaned with a proper reamer. Once the directional core drilling phase was completed at around 600 m (1968.5 ft) depth, we switched to normal diamond core drilling and drilled all the way to the target at 1218 m (3996 ft). The last target was cut from the branch at 561 m (1841.6 ft) and steered to 1118 m (3668 ft). The cutting method in directional core drilling is more recommended than using a wedge to form branches, as the wedge always adds one more variable to account for in drilling and may cause issues in terms of friction and losing rods in the hole.
The results in Kevitsa were satisfying for Boliden, thus they have decided to use the same directional core drilling method again in Kevitsa starting in October 2022 with the ADC K2 rig and crew.
In conclusion, this is only one of the examples where ADC has used the AZIDRILL tool to help customers reach their targets. Additionally, Aziwell has been working successfully globally on projects with the same tool that has been proven reliable to use, even when the hole needs to be steered at 2000 m (6560 ft) depth to hit the target.
ADC remains a diamond drilling company, but we aim to expand further our exploration capacity and possibilities through directional core drilling.
About the company
ADC’s history goes back to 2004. Since then the company has quickly grown to the largest diamond core drilling company in Scandinavia. ADC offers diamond core drilling, BOT drilling and RC drilling services. The company has long roots in R&D, which has also led to drill rig manufacturing and sales on the global market. ADC is certified for ISO9001, ISO14001 and ISO45001 to ensure high-quality and environmentally friendly operations and employees’ safety during drilling.
For more information visit: www.adcltd.fi/en/
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