The future of mineral exploration comes to South Australia: field trial of coiled tubing drilling rig
The South Australian Government’s partnership with the Deep Exploration Technologies CRC has been about the collaborative journey towards transforming mineral exploration in areas of deeply covered geology.
The ambitious aim of developing a coiled tubing (CT) drilling rig for hard-rock mineral exploration promised drilling that would be cheaper and faster. This is not only transformational for mineral explorers, but also provides geological surveys with the means to effectively sample and map rocks under cover.
In February and March 2017, the recently launched RoXplorer® underwent a trial in the northeastern Eyre Peninsula with the aim of drilling a 20 m interval in one hour, a 400 m hole in four 12-hour shifts and the recovery of cuttings representative of the geology in a previously drilled, adjacent diamond drillhole. The trial was facilitated by Geological Survey of South Australia (GSSA) staff who assisted with permitting, logistics, safety, and geological and other matters.
The RoXplorer® is the name given to the Deep Exploration Technologies Cooperative Research Centre (DET CRC) new CT drilling rig which has been designed and manufactured in South Australia. CT drilling has previously been used in the oil and gas industry. Rather than using a series of drill rods as with conventional drilling, the CT rig utilises a continuous steel coil (currently 500 m) from a large reel mounted at the top of the mast. This significantly reduces the time, expense and manual handling required to enter and pull up out of a hole, which is one of several reasons the RoXplorer® aims to achieve a cost per metre as low as $50. The drill string cannot rotate and the drill bit is driven by downhole motors or turbines themselves driven by fluid pressure in the hole.
Since the launch of the RoXplorer® in November 2016, the rig has been undergoing intensive testing. The initial challenge was to achieve rapid penetration in hard rock. This has been accomplished during testing at the Brukunga drillsite. One of the many challenges facing this new method to the minerals industry, and one which is pertinent to its future success and that of exploration more generally, is to rapidly penetrate both soft and hard ground within thick cover rocks. This underlines the importance of trialling CT drilling in a range of conditions.
The recent trial took place alongside the previously drilled MSDP02 drillhole near Port Augusta, completed as part of the GSSA’s Mineral Systems Drilling Program. The site offered an example of typical thick cover and provided several geological challenges. Six metres of cobble conglomerate at the top of the hole, followed by about 400 m of Adelaidean shale and sandstone which include Tregolana Shale, Yerelina Subgroup and Tapley Hill Formation. Underlying these units is Neoproterozoic Beda Basalt, with physical characteristics similar to fresh ‘basement’ rocks.
RoXplorer® drilled in the surface casing to 27 m, then drilled the first 20 m below the casing in 56 minutes and achieved 115 m in the first day. Rates of penetration were up to an impressive 450 mm/minute, proving that the method can exceed 100 m per shift. As with any drilling program, especially the first remote trial of a revolutionary new drill rig, there were challenges, especially with the downhole motors. At the end of the fourth day of drilling, the RoXplorer® had drilled to a depth of 367 m and the hole was later terminated at 410 m. Nonetheless, an average of 92 m/shift over four days, when diamond drilling achieved ~20 m/shift in the adjacent hole, is an exciting start. Furthermore, initial analysis of the cuttings suggests that geological contacts are sharply defined.
While it is very early days for the RoXplorer®, the DET CRC looks to have provided a step-change to the minerals industry. With further development, CT drilling could well be an important part of the future of mineral exploration. An incredible achievement from a dedicated team of people who are making the DET CRC’s vision a reality.
A final field trial at a yet to be determined location is planned for mid 2017 before the DET CRC reaches its completion date of 30 June 2018.
– Adrian Fabris