Prediction of shale bedding-parallel crack density based on the SH-SH wave inversion of the VTI media

Abstract

Bedding-parallel cracks relate to hydrocarbon accumulation and can be beneficial for hydraulic fracturing. The prediction of bedding-parallel crack density (BCD) from seismic data is difficult because the development of bedding-parallel cracks has limited effects on the velocities and density of subsurface formation. Well logs of the Qingshankou (K2qn) shales in the Songliao Basin, northeast China, reveal that the target formations represent extremely strong seismic anisotropy (> 40%), and the magnitude of S-wave anisotropy highly relates to the density of bedding-parallel cracks (up to 2500 m−1). We present a novel BCD prediction method using the reflected seismic shear wave. The S-wave anisotropy parameter γ is first inverted from the SH-SH wave by using a stepwise inversion method based on a new shear wave reflection coefficient approximation. Furthermore, the highly correlated rock-physics relationship between BCD and the anisotropy parameter γ facilitates accurate BCD estimation. Field data application on a real seismic shear wave data set acquired from the study area demonstrates the viability of the proposed method. The investigation provides a useful tool for the characterization of ‘sweet-spots’ of shale-oil reservoir formation.