A refraction‐seismic field study to determine the anisotropic parameters of shales

Abstract

Shales are known to be transversely isotropic (TI), which can lead to incorrect subsurface imaging if isotropic behavior is assumed. By knowing the anisotropic parameters of the shales, it is possible to correct for the anisotropic effects in seismic data, thereby obtaining a more correct subsurface image. Two P-wave refraction‐seismic field studies were undertaken in areas of steeply dipping marine shales of the Wapiabi Formation to determine the anisotropic parameters of these shales in situ. The first survey was located in Jumpingpound Creek, Alberta, Canada, and the other location was west of Longview, Alberta, Canada. Seismic lines were laid out parallel, perpendicular, and 45° to the local strike directions. At both locations, the compressional headwave velocities along strike were determined to be faster than the velocities perpendicular to strike. Analysis of the Jumpingpound Creek data location yielded anisotropic parameters of ε = 0.14 ± 0.05 and δ = 0.00 ± 0.08, whereas at Longview, the anisotropic parameters were determined to be ε = 0.25 ± 0.06 and δ = 0.00 ± 0.06. The difference in ε is attributed to variations in the shale facies between the two sites.