Underground » Geology
CRCMining is developing a system called In Seam Wireless Drill String (ISWDS) for providing high data rate, bidirectional wireless communication between the BHA and the drill rig in the hazardous conditions of Underground In-Seam (UIS) drilling. This report details the work conducted in Phase 1 of the project, where the performance of the wireless electromagnetic telemetry (EMT) signal was successfully assessed using a research prototype tool. Excellent results were obtained in a 320m long UIS borehole at Tahmoor in July 2014. Based on these results, it is now possible to develop a commercially operable tool for cross panel drilling, or more generally, for holes in the 4-500m range. A second phase of R&D is commencing in 2015 to develop the system, and conduct further research for assessing and optimizing the performance in the 800m-1200m range.
The aim of the wireless technology is to provide the following:
· Open up the market for a wide range of geological survey technologies; which can potentially bring a step change to standard drilling practice;
· Replace wired drill rods with standard hollow rods, which will improve rod handling as well as enable wire-line logging technologies and fishing of stuck tools to be implemented underground. This will transform the risk profile of measure while drilling BHA's; and
· Reduce capital cost of rods and survey equipment.
The capital cost of existing technologies for UIS drilling is approximately $220,000 for 1,200m of drill rods with the modifications required for enabling telemetry, and approximately $330,000 for the MWD system. Alternate technologies could reduce the cost by $150,000 for an MWD system with a set of drill rods. The operating cost of drilling is largely dependent on the quality of the meters achieved. The yearly cost of inseam drilling is close to $8M per mine. The mines that CRCMining surveyed reported that the quality of the meters drilled was as low as 50% when drilling flank holes, and average at 80% during cross panel drilling. Thus, if the driller has real-time feedback of what lies ahead of the drill bit, steering decisions could be made ahead of time that would improve drilling costs significantly. This could then pave the way for the future automation of drilling, which would further improve the quality of drilling and eliminate operator errors.
We demonstrate in the report that when drilling outside of the coal seam, such as in a cross measure hole, reliable high bandwidth EM signals are achievable in the initial 5-800m. But, when the drill string is predominately inside the coal seam there will be less signal losses, and thus distances beyond 1000m are possible even with the power limitations of an intrinsically safe design. The field tests that were conducted in phase 1 demonstrated that the signal loss at the 320m test distance was very low, and hence a very strong and high quality signal was achieved; even when the transmitter output current was only one tenth of the current that is acceptable for an intrinsically safe design. A very large volume of data has also been collected to study the characteristics of the signal propagation in the coal seam and to define the specifications for an optimal design.