High-resolution 3-D seismic survey over a coal mine reserve area in the U.S.—A case study

A high-resolution three-dimensional (3-D) seismic survey was conducted in advance of coal mine development in the Illinois basin in May 1989 to better define a geologic structure with the potential to adversely affect longwall mining conditions. The 3-D seismic data indicate that an abrupt change in seam elevation, or roll, encountered near the northern property line trends south into the reserve area and then turns southeast. A personal computer–based workstation was used to integrate borehole and seismic data for modeling in which 3-D block diagrams of the calculated seam elevations were generated. The block diagrams show a steep slope on the west flank of the roll that gradually decreases as the roll turns to the southeast. The survey also reveals a geologic structure beneath the roll at an estimated depth of 46–62 m. Horizontal time-slice sections of this feature suggest the presence of a paleochannel that meanders on a similar course as the roll, which apparently was connected to a larger paleochannel system. A Conoco high-frequency vibroseis unit was successfully used as the seismic source to generate the high frequencies necessary to detect and resolve the thin coal beds.