Seismic inversion for coal‐seam thicknesses: trials from the Belvoir coalfield, England[Link]

We have applied generalized linear inversion to high‐quality seismic reflection data from the Coal Measures in the East Midlands of England. The purpose was to test whether accurate values for coal‐seam thicknesses could be obtained to benefit longwall coal‐mining and coal‐bed methane production. A seismic line intersecting two logged boreholes was chosen so that an objective evaluation of the results could be made, and inversion was carried out after careful reprocessing of the line with post‐stack migration. As coal‐seams are thin beds in the seismic bandwidth, it was necessary to assume that acoustic impedance values are constant. Of the ten coal‐seams in the sequence, only two were found to be major contributors to the reflection response at the boreholes, but inversion runs were carried out independently for two seams and four seams. It was found that keeping the wavelet fixed was the best strategy when inverting for the interface two‐way times at the seam boundaries. However, all the strategies tested showed inconsistent variations in seam thicknesses which were geologically implausible. We conclude that significant improvements need to be made in acquisition and processing techniques for inversion to give useful results in this application.