Overburden measurement for coal mine management with 3D high resolution compressional and shear velocity seismic inversion

High resolution surface seismic surveys can provide useful images of coal bed reflections to depths as shallow as 50 to 100 metres. There is also a need, to gain information of the overburden properties above these depths. This information gap can be addressed by inversion of both the refractions and surface waves (`ground-roll', normally considered to be noise) generated along with reflections as part of the regular survey acquisition. Recent advances in acquisition such as finer spatial sampling, single sensor recording and lower frequency vibroseis sweeps all serve to improve the quality and utility of these data. In addition to their direct use to infer the petrophysical and hydrodynamic properties of the overburden prior to stripping and mining, the results can be used in reflection seismic imaging. As the compressional velocity (Vp) result is in depth, it can be used for both statics computation and directly as the shallow part of a depth imaging velocity model where reflection-based velocity derivation is poor. The shear velocity (Vs) information can also be used to create a model for subtractive attenuation of the ground-roll for subsequent reflection imaging. This paper demonstrates how detailed 3D volumes of both Vp and Vs velocities have been co-operatively inverted from diving and surface waves respectively, directly into the depth domain over coal mining leases in Queensland, Australia.