David W. King
Seismic reflection techniques are widely exploited in exploration for hydrocarbons, and consequently have reached a high state of development. Improvements in resolution and fidelity of recorded information and in techniques for extracting and interpreting information contained in recorded data are such that seismic techniques are increasingly attractive in both the resource-evaluation and mine-planning aspects of coal exploration. Field, processing, and interpretation methods consistent with the vertical and lateral resolution necessary for delineation of fine structure in a coal-bearing section differ significantly from those which are praxis in seismic exploration for hydrocarbon-bearing structures.
The key to improved resolution lies in maximizing signal bandwidth and dominant frequency, and minimizing signal-generated and other noise. Explosive charges detonated below the geophysically weathered layer are the richest source of high frequencies available for seismic work; for high resolution, the smallest charges capable of providing the required penetration are preferred on the basis that the source spectra are displaced to higher frequencies. The technology necessary for detecting and recording high-frequency information can be specified accurately in terms of dynamic range, bandwidth, and frequency discrimination. Processing high-resolution data is conceptually simple but demands extreme care.
Notwithstanding the capabilities of high-resolution seismic techniques, maximum resolution is ultimately limited by the complexity of the earth. In particular, the resolution of multiple seams is limited by internal multiples, which have a higher frequency content than transmitted primaries. Reflection data from two markedly different coal-bearing sections in Australia illustrate the scope and, indirectly, the viability of seismic exploration for coal.
AAPG Search and Discovery Article #90962©1978 AAPG 2nd Circum-Pacific Energy and Minerals Resource Conference, Honolulu, Hawaii