Assessment of a Geophysical Coal Exploration Method Completed

The final technical report for the assessment of a geophysical coal exploration method was submitted to the Illinois Clean Coal Institute. The focus of these coal exploration projects are to accurately and cost effectively predict the geology of a coal field. More geologic data generally yield a better geological model of the coal field. Advances in geophysical methods may provide tools to supplement the traditional methods of coal exploration. In this study, two seismic methods, multi-channel analysis of surface waves (MASW) and shear wave (SH-wave) analysis, were evaluated to determine their usefulness as coal exploration tools. It was determined that (1) the MASW method was useful to model the relief on the bedrock surface. Because the geophone spacing was 5 feet, the mapping of the unconsolidated material thickness was very accurate compared with results using a typical coal exploration program. The method was not useful in modeling below the bedrock surface due to its poor vertical resolution and limited depth of penetration. (2) The SH-wave survey was able to accurately model bedrock down to 150 to 200 feet below the surface. Amplitude change, or the tuning effect, was useful to image the existing thin (less than 5 feet) coal layers. This method also allowed prediction of locations of igneous dikes, which intrude through the coal seams in this region. Two-dimensional geologic models constructed with this method were very useful in visualizing complex fault zones. This report contains data pertaining to coal thickness, depth to coals, chemical analyses of coal (sulfur, BTUs, moisture, ash), geophysical models, and stratigraphic correlations. The project was located in Saline County approximately 5 miles southeast of Harrisburg, Illinois.