On discriminating sand from shale using prestack inversion without wells: A proof of concept using well data as a surrogate for seismic amplitudes

Abstract

A new method has been developed to discriminate sand from shale, from P-wave velocity, S-wave velocity, and density values obtained from elastic seismic inversion without well control. The method, based on empirical or semiempirical principles, has been tested with well data in thick Tertiary clastic columns in the Gulf of Mexico, where the input data (compressional and shear sonic logs and bulk density) are of good quality and where there is a lithology log to verify results. The method cannot be applied to gas-bearing sands. Gas sands should be separated prior to application of the method using, for instance, the VP/VS values as a criterion. A preliminary discrimination of sand from shale in areas without well control is indeed a useful exploration tool. It is also very useful in pore-pressure calculations in which, ideally, only shale points should be used to determine the normal compaction trend.