Anisotropy and attenuation of crosshole channel waves from the Antrim Shale gas play, Michigan Basin

Abstract

We analyze the crosshole data from the Antrim Shale gas play at the MIT test site in the Michigan Basin. A crosshole seismic logging analysis has revealed the presence of strong transverse isotropy possibly due to the alignment of clay platelets along the bedding plane or sedimentary bedding, and strong continuity in the depth interval covered in this study. We find that the data are dominated by channel waves associated with low velocity zones (waveguides) identified in the sonic logs. Channel waves are characterized by their unique characteristics, such as dispersion and amplitude variation with depth. The channel-wave analysis has revealed the possible presence of azimuthal anisotropy at the top of the depth covered in this survey, which may be related to fracturing in the Antrim Shale formation. The data also show strong attenuation of S-waves characterized by very low frequency contents which may be due to viscoelastic properties of shaly sands or scattering by fractures. However, direct estimates of fracture parameters are not possible due to the limited data available. Finally, we have modeled the data with synthetic seismograms using a model with a 30% anisotropy.