Geophysics at the coal-face

Abstract

Coal is a low-cost commodity and coal miners profit margins are slim, such that mining companies must maintain tight cost control to achieve acceptable returns. The challenge to coal geophysics is to adapt to these economic constraints and provide cost-effective, reliable methods for exploration and mining requirements. The geophysical methods which have been used in the reconnaissance, pre-development, and operational stages of coal exploration and mining are reviewed in terms of their exploratory function and their typical frequency of application. Borehole logging is the one method which is highly utilised for both surface and underground coal mining exploration, although seismic methods (mainly high-resolution reflection, and in-seam), are also frequently applied in underground coal-mining investigations. Because surface coal mining is constrained to shallow seams, most exploration is achieved by drilling methods, with geophysics playing a supporting but subordinate role. Also surface mining is less sensitive to seam disturbances such as faulting, rolls and intrusions, and can afford to set less strict requirements for prediction and resolution. The trend in underground mining is towards high-production longwall methods, which are much less tolerant of disturbance, and demand survey reliability and resolution standards which often stretch the limits of current exploration technology. A Workshop on Underground Coal Mining Exploration Techniques was conducted by the Australian Coal Association in 1991 to identify the strategies and priorities for future research and development. Most of the recommendations coming from the Workshop incorporated geophysical technologies, particularly the development of borehole logging methods which can be applied to in-seam drillholes. The recommendations also identified the need to selectively import and adapt analogous but more advanced technology from other areas, such as seismic reflection expertise from the petroleum industry, and to consolidate on the promising beginnings shown by techniques such as the radio-imaging method and in-seam seismic. The future also holds opportunities for geophysics to assist in the development and application of innovative mining systems. High-wall mining, continuous surface miners, and the increasing trend towards high-production automated mining equipment, bring with them the need to provide geophysical monitoring sensors and guidance systems.