Radio-wave imaging in a coal seam waveguide using a pre-selected enforced resonant mode

The efficacy of radio-wave imaging (RIM) in extended geological strata which are planar and regular, such as coal seams, continues to be questioned, because the electromagnetic wave excitation and propagation mechanisms remain unclear. To eradicate the doubts, a full-wave finite element simulation of a ‘realistic’ coal seam boundary value problem has been constructed and is described and analysed in this paper. The model is used to examine electromagnetic waves (near-fields) in the vicinity of the magnetic source and resonant modal patterns distant from it, for a range of electrical parameters for the coal medium and for a variety of possible boundary conditions. These studies suggest that only for very low loss seams can RIM be effective, and consequently a new guided electromagnetic wave (GEM) system has been proposed to circumvent the acknowledged deficiencies inherent in RIM.

► A full-wave electromagnetic simulation of a large regularly shaped geological stratum is described.
► Modelling results are generated for a wide range of scenarios with relevance to radiowave probing of coal seams.
► Electromagnetic modes are feasible in a 1000 m long, 300 m wide and 6 m high, ‘regular’ geological stratum.
► Moding can occur in lossy structures such as coal seams provided the electrical conductivity is not too large.