Imaging coal seam structure using 3-D seismic methods

Abstract

Coal mining and production is a very large industry within Australia with over 100 active collieries. However, to run at a profit, the coal mines must have continuous production and fulfil large annual quotas. This is generally achieved through the use of the capital intensive, underground, longwall mining technique. This technique requires that the coal seam structure be accurately known ahead of the extraction coal face. Any unknown faulting, unstable roof conditions or gas accumulations encountered while mining can lead to equipment damage, down-time and injury to workers. Thus, the responsibility is on the mine geologist to ensure that the coal seam structure is accurately mapped ahead of mining, to provide a safe mine plan. Before the introduction of the seismic method in coal mining, all coal seam mapping was done using surface boreholes. This is an expensive method to use and provides only a low level of lateral resolution. Seismic methods are gradually replacing boreholes and becoming more common place in coal industry as an accurate and cost effective alternative method for imaging the seam structure. Burton Downs colliery in central Queensland, was one such mine to take advantage of this method as apart of an Underground Feasibility Study for their northern, Kerlong mine area. With no previous seismic work done in the area, reverse vertical seismic profiling (RVSP) and two-dimensional (2-D) surveys were initially shot. RVSP results showed that the seismic method was viable, imaging the coal seam of interest and provided acquisition parameters for the 2-D surveys. The 2-D lines gave high-resolution images of the coal seams within the mine area, and showed a complex faulting system which included low-angle reverse faulting and normal faulting. The success of the 2-D profiles prompted the acquisition of a three-dimensional (3-D) survey. After processing the 3-D depth volume, a much more complete structural interpretation and hence, mine plan could be made.