Using Helicopter Tdem Surveys To Identify Flooded Workings In Underground Coal Mines; The First Attempt

Abstract

The U.S. Department of Energy’s National Energy Technology Laboratory (NETL) has used helicopter-mounted electromagnetic (HEM) surveys to identify mine pools within active and abandoned underground coal mines in the eastern United States. Two types of HEM surveys have been tested: frequency domain electromagnetic (FDEM) and time domain electromagnetic (TDEM). Previous surveys have indicated that FDEM surveys can identify flooded mine workings in areas where overburden is less than 50-m thick. However, most mines are deeper than 50 m. This survey attempted to use helicopter TDEM to locate deep, flooded mine workings at challenging sites in southwestern Virginia, an area containing multiple levels of mining, thin seams, and mine water of relatively low conductivity. The rationale behind this choice of field sites was that if the technology worked in this admittedly difficult region, it could be applied to any coalfield. However, the survey was unsuccessful; mine workings known to be flooded were not detected. This paper discusses problems that were encountered, particularly electromagnetic noise, which rendered 25-50 pct of each flight line unusable.