Evolution and application of in-seam drilling for gas drainage
The presence of seam gas in the form of methane or carbon dioxide presents a hazard to underground coal mining operations. In-seam drilling has been undertaken for the past three decades for gas drainage to reduce the risk of gas outburst and lower the concentrations of seam gas in the underground ventilation. The drilling practices have reflected the standards of the times and have evolved with the development of technology and equipment and the needs to provide a safe mining environment underground. Early practice was to adapt equipment from other fields, with rotary drilling being the only form of drilling available. This form of drainage allowed various levels of gas drainage coverage but with changing emphasis, research and development within the coal industry has created specific equipment, technology and practices to accurately place in-seam boreholes to provide efficient and effective gas drainage. Research into gas content determination established a standard for the process and safe levels for mining operations to continue. Surveying technology improved from the wire-line, single-shot Eastman survey instruments which was time-dependent on borehole depth to electronic instruments located in the drill string which transmitted accurate survey data to the drilling crew without time delays. This allowed improved directional control and increased drilling rates. Directional drilling technology has now been established as the industry standard to provide effective gas drainage drilling. Exploration was identified as an additional benefit with directional drilling as it has the ability to provide exploration data from long boreholes. The ability of the technology to provide safe and reliable means to investigate the need for inrush protection and water drainage ahead of mining has been established. Directional drilling technology has now been introduced to the Chinese coal industry for gas drainage through a practice of auditing, design, supply, training and ongoing support. Experienced drilling crews can offer site specific gas drainage drilling services utilising the latest equipment and technology.