Coal seismic depth conversion for mine data integration: a case study from the Sandy Creek 3D seismic survey

Abstract

When seismic data are presented as two-way reflection times, these times are not easily directly scalable to depths, because of spatial variations of seismic velocity. Apparent structures in the time domain can be misleading. Correct conversion of seismic time sections to depth sections removes this ambiguity. In general, seismic depth conversion is a complex process requiring careful use of NMO and migration velocities, the study of well data, and the generation of synthetic seismograms. The process is usually iterative, especially when the structures are complex. In this paper, we present a depth-conversion algorithm designed for coal seismic data. Our method exploits the relatively simple structure of coal seams and the availability of many exploration boreholes to constrain the process. Once converted to depth, the seismic data can be exported into mine-planning software and used to provide seam elevations for tasks such as in-seam drilling and other mine activities. Our method has been implemented into an MS Windows-based program, and allows new boreholes to be incorporated without the need to go back to a seismic processing centre. A 3D seismic data set from Xstrata?s Sandy Creek coal mine is used to demonstrate our method. The results show that the depth-conversion algorithm can accommodate differences in seismic processing. The depth-converted seismic data agrees with the geological model based on the borehole results and underground mine surveys. Given confidence in the depth conversion, it is possible to look more closely into the seismic data in order to make interpretations that are more detailed.