Delineation of a coal burn edge with seismic refraction

Coal seams in many areas of western United States have ignited and burned for considerble distances underground. Burning reduces the coal reserves and alters the overburden to highly fractured clinker. The boundary between the coal and the clinker needs to be defined for determination of reserves and for planning seismic petroleum exploration in these areas. A seismic refraction method was tested that may possess advantages over previous techniques for locating the burned zone edge. Field tests were conducted at Kerr-McGee Coal Corp.'s open pit Clovis Point mine near Gillette, Wyoming. Explosive sources were detonated in shot holes in the pit floor. Geophone lines were laid on the surface beyond the edge of the pit. The lines crossed from an area of known coal to an area of clinker. Delays in arrival times were found to correlate with the expected beginning of the clinker zone. Waves passing through the clinker also exhibit a significant attenuation. A magnetic survey conducted along the seismic lines showed anomalies in the regions where seismic data indicated the burn edge. On the basis of these results, this technique shows potential for locating burn edges where other methods do not work well and where it may be less expensive than extensive drilling.