Underground » Ventilation, Gas Drainage and Monitoring
Gas drainage is a major issue currently affecting underground coal mines. The difficulties associated with underground gas drainage are partly responsible for the poor development rates for longwall coal blocks; these in turn limit coal production from underground operations. In an effort to improve longwall productivity, and address current safety issues associated with methane drainage, the CMTE has been investigating the applicability of high pressure waterjet drilling for gas drainage in underground mines. The technology has the capability for high productivity and with steering could significantly reduce gas drainage drilling costs.
The overall aim of the ACARP supported project (C7024) is to produce a high speed cross panel drilling system which has productivity characteristics and a drilling accuracy far exceeding that of current drilling systems. The work has been split into two stages; Stage 1 (the focus of this report) develops the guidance (surveying and steerage) of the drilling tool and Stage 2 takes the technology to the underground demonstration stage.
From trials conducted at Moura Mine (BHP Coal), a dead reckoning navigation tool has been produced. The position of the drilling tool is reported out of the hole in real time while drilling. This is the first time that this has been achieved. With conventional drilling techniques, drilling has to be stopped and a survey point taken which adversely affects productivity. Jet thruster steerage has also been demonstrated to change the borehole trajectory in a controlled and predictable fashion. Steerage has yet to be activated in real time, however a positional motor to orientate the jet thruster has been tested in the laboratory.
The findings from Stage 1 indicate that the development of a waterjet drilling tool for producing underground gas drainage boreholes is not far away. Stage 2 should take the system to the point where an underground demonstration can be performed in an underground coal mine. The technology has the potential to have significant productivity gains, which could at least halve underground gas drainage drilling costs.