Underground » Geology
The primary objective of this project was to compare geophysical data from two different technologies, the Radio Imaging Method (RIM) and In-Seam Seismic (ISS), with a view to minimising geological risk in a longwall operation. Conceptually, data from an electromagnetic technology (RIM) should provide complementary information to that derived from seismic signals (sonic). Together, the risk mitigation potential should be greater than that with either technology alone.
A site was chosen for the trial (Mine X) in an area with a number of geological structures, including conglomerate erosional features (washouts), faults, and multiple zones of intraformational breccia. The faults and conglomerate washouts have high potential impact upon longwall operations. The site available for the trial exhibited a high degree of geological complexity relative to the norm for Australian coal mining.
RIM has been active in Australia for more than 30 years and can be sourced through a local supplier. ISS has not been available in Australia for the past two decades and required mobilisation of a specialist team from Germany. An additional technology (Yabby Geosensing) that was unavailable at the time of the project conceptualisation has been included in this analysis, as it provided complementary geological information and 'ground-truthing' of the geophysical interpretation.
RIM and ISS clearly identified anomalous zones in similar parts of the longwall panel investigated - thus, they reinforced each other. Both techniques proved useful for identifying areas of 'clear coal' as well as areas affected by geological structure. The waveguide and local EM properties for RIM were not optimal, and resolution suffered consequently. ISS provided a more detailed interpretation and appeared to respond well to faults (via Love Wave analysis) and washouts (via Raleigh Wave analysis).
RIM and ISS provided excellent targets for further investigation. This was subsequently undertaken using a UIS drilling rig fitted with a Yabby Geosensing unit.
The results from the Yabby work provided a high level of resolution of geological features identified as anomalies by the geophysics, and a high-confidence geological model. A broad analogy with medicine is that the geophysics provided the full body scan, and the Yabby data provided the biopsy. The combination of EM geophysics (RIM), seismic and geosensing is a very powerful risk mitigation suite of tools for a modern longwall operation. The use of these technologies in tandem all but guarantees 'no surprises' in a prospective longwall panel - thus longwall geological risk minimisation can be achieved. The final geo-model could and should be used as an essential input to longwall automation.
The ISS work was sufficiently encouraging to suggest that routine use in Australian coal mining is advisable.