Called Tight-Radius Drilling (TRD), the technology has been developed and is being commercialised by the Brisbane-based Cooperative Research Centre for Mining Technology and Equipment (CMTE), in collaboration with industry partner BHP Mitsui Coal.
The technology has been demonstrated in field trials at BHP’s former Moura mine and Anglo Coal’s new Grasstree development project. An initial trial at BHP’s Moura mine produced in the region of 1 terajoule per day. CMTE industry member Anglo has plans to conduct further work with TRD to pre-drain methane from coal seams at the Grasstree project in central Queensland prior to mining.
CMTE chief executive officer Dr Michael Hood said the technology enabled coal to be drained of highly-explosive methane gas well in advance of mining, eliminating the current need for humans and infrastructure to go underground and potentially saving millions of dollars for Australian coal mines.
"Tight-radius drilling also provides a cost-effective way to harness what is a huge, environmentally-friendly source of energy," Hood said.
The system is lowered into a conventional vertical well to the depth of a coal seam, where a specially-developed water jet cutting device drills out laterally into the coal. The device can drill in any direction, creating as many holes as necessary, and can be lowered or raised to work in multiple coal seams.
The specially-developed water jet cutting device drills out laterally into the coal. It can drill in any direction, creating as many holes as necessary.
The holes drilled increase the permeability of the coal seam, allowing methane to find a pathway to the surface, once the water used by the drill is pumped out.
Tight-radius drilling differs from the more conventional medium-radius drilling in that it can drill multiple coal seams in multiple directions. Once sunk, the water-jet is turned on a 1 foot radius in each seam horizon (medium-radius drilling turns on a 100m radius). Hood said this meant that multiple holes can be drilled in every seam at all points of the compass at very low cost. At present the length of the radial hole has been tested to around 200m and Hood said going longer would be possible with some testing in the near future.
The drill already includes a built-in survey tool that enables mine planners to identify where the holes have been drilled. Another sensor is currently in development that will allow the measurement of the roof and/or floor with respect to the drill, and provide a map of the seam geometry prior to mining. Another improvement will be the development of a steering mechanism which will allow greater manipulation of the drill in-seam.
The technology is being commercialised through a spin-off company, CBM Innovations, which owns the intellectual property to the technology. Two markets areas are being targeted. One is draining seams prior to mining. The other is the rapidly expanding worldwide market using coalbed methane as a source of greenhouse gas friendly energy.
Hood said the technology has attracted considerable interest in Europe, the United States and China. This novel drilling service is available to clients offered on a time and materials basis at present, he said.
"The technology is now being prepared to meet commercial demand, with plans to mount the system on a purpose-built truck to allow rapid mobilisation from one vertical well to the next," Hood said.
CMTE and BHP Mitsui Coal received an Award for Technology Transfer for their collaborative efforts to develop and deliver the technology to industry. The award was presented on May 15 at the Cooperative Research Centres' Association Conference in Perth.