Efficient exploratory drilling is one of the most important tasks in the whole mining process. Maurice Jones reports
With the importance of exploratory drilling closely related to the value of the mineral deposits being sought and the difficulty of reaching them, it follows that whatever can be done to improve the cost-effectiveness of exploratory bores should pay substantial dividends. This is where directional drilling, especially including core drilling, comes in.
Directional drilling allows geological information to be collected over a wide area, or volume, of ground from one drill primary set-up. This is achieved by drilling holes with a planned curved path rather than straight. With directional control and accurate hole surveying several holes can be drilled from the one rig position to cover the zone of interest, rather than having to move the rig for a number of straight holes and to drilling more metres overall.
Directional drilling was first developed for oil- and gas-field use, for production wells as well as exploration. Since then it has been adapted to many other forms of strata drilling including geothermal energy, site investigation for civil engineering, pipeline installation (HDD – horizontal directional drilling), coal-bed methane drainage, underground rescue, and mineral exploration.
Hole surveying and coring
The technology of directional drilling itself is comparatively well established, at least with leading practitioners, with the main technical advances coming in hole surveying and coring. Both are essential for full information about the location of each hole and the type of strata being passed through. Measurement-While-Drilling (MWD) is now possible with both wired and wireless communication to the drill-rig, saving time and set-ups for long and/or less stable holes.
Devico of Norway has been an innovator in directional core drilling since it establishment. The company has been recently engaged in a four-year directional drilling programme with Agnico-Eagle at Kittilä mining. Devico also offers its expertise in co-operation with other drilling companies, including the Artic Drilling Company. Orbit Garant Drilling of Canada, Kati, Protech, Drillcon, Smoy, Styrud , Artic Geodrilling and E-Service of Norway. The Orbit Garant work this year included directional deviation at depths around 1900m. In South Africa Devico has been working with Northam Platinum to carry out underground core drilling from In-reef ‘horizontal’ holes and deviations to reach other zones of interest. Coring while deviating the hole by 25-30 deg is possible to avoid losing any material. Operations employ the DeviDrill steerable, wireline-operated core barrel.
Devico’s latest development is the DeviShot multishot borehole magnetic survey tool. It employs DeviSoft mobile software and wireless communications to connect with the operators, providing quick results for plotting and analysis.
Another operator that specialises in directional drilling at or to great depths is Murray & Roberts of South Africa . It has carried out DTH motor directional drilling to around 3000m below the surface including to rigs working to 2500m in Anglo old Ashanti developments in Ghana.
The Layne Christensen Group, HQed in the US, offers both directional core-drilling contracting services and equipment through the Layne Mineral Exploration Division and IDS respectively. IDS offers equipment and services including directional hole planning, MWD solutions, Accu-Dril directional down-hole motors and other directional drilling equipment.
Video: Exploratory drilling for uranium ore in northern Saskatchewan, Canada using directional core drilling. The drilling is being carried out by TEAM Drilling for the UEX Corp. and AREVA Resources Canada Inc.