Application of seismic lithology inversion in identifying sandstone of coalbed roof

The main target strata of EXB mining area are a set of flood plain coal-bearing clastic sedimentary strata. The roof lithology of the coal seam changes rapidly and the lithology prediction is difficult. This paper used logging petrophysics analysis to establish the histogram of wave impedance of coal, medium sandstone, fine sandstone and shale sandstone. The impedance of coal was small with an upper limit of 7 500 m/s·(g/cm³). The impedance range of medium sandstone was between 5 500 and 10 000 m/s·(g/cm³). Elastic properties of fine sandstone and shale sandstone were close and indistinguishable in impedance. So the two rocks were merged and their impedance range was 6 000~12 000 m/s·(g/cm³). The seismic impedance volume was calculated by poststack inversion, and the facies and fluids probabilities analysis were applied to predict the spatial distribution of the roof lithology. The result shows that macroscopic change of lithology and its thickness predicted by seismic inversion was consistent with drilling results and lithologically the law of planar distribution of thickness agreed with sedimentary environment.