Advanced directional drilling technology for gas drainage and exploration in Australian coal mines

Abstract

With the continuing technology innovation, directional drilling technology has provided the coal mining industry with effective and practical options for pre- and post-drainage and exploration in Australia. In the past thirty years, in-mine borehole steering equipment has been developed from the single shot camera survey systems to the advanced Directional Drill Monitor utilizing Modular Electrically Connected Cable Assembly (DDM-MECCA) survey instruments, which provides rapid and easy underground borehole survey measurements whilst drilling. The presence of coal seam gas such as methane poses a significant safety hazard to underground coal mining all over the world. However, gas can be captured using pre- and post-drainage techniques to improve coal production, energy recovery, enhance safety, environmental mitigation. An additional benefit of directional drilling is geological explorations in advance of mining. As any discontinuities intercepted during in-seam directional drilling, such as faults, folds and igneous intrusions, can be monitored by drilling fluid pressures, changes in thrust, vibration, rate of penetration and inspection of cuttings. Directional drilling technologies offer coal operators a cost effective exploration alternative without speculation. Applications of the directional drilling technologies in Australian coal mines have established the benefits of the methodology for gas control and geological explorations. Directionally drilled flank boreholes provide shielding to the gate entry developments, horizontal goaf boreholes for gas drainage in deep multi-level mines, and hydro fracturing and exploration in advance of mining. However, there still remains four major problems associated with directionally drilling, and these include: sticky drilling in complex conditions, sensitivity of down hole probe, in-hole stability and drill depth capacity.