SEISMIC INVERSION FOR COAL-SEAM THICKNESSES - TRIALS FROM THE BELVOIRCOALFIELD, ENGLAND

We have applied generalized linear inversion to high-duality seismic r eflection data from the Coal Measures in the East Midlands of England. The purpose was to test whether accurate values for coal-seam thickne sses could be obtained to benefit longwall coal-mining and coal-bed me thane 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 w ith post-stack migration. As coal-seams are thin beds in the seismic b andwidth, it was necessary to assume that acoustic impedance values ar e 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 f our seams. It was found that keeping the wavelet fixed was the best st rategy when inverting for the interface two-way times at the seam boun daries. However, all the strategies tested showed inconsistent variati ons in seam thicknesses which were geologically implausible. We conclu de that significant improvements need to be made in acquisition and pr ocessing techniques for inversion to give useful results in this appli cation.