Anisotropic Kirchhoff Migration with Input from Wireline Logs

Summary Skew angle ultrasonic velocity measurements have been performed on plugs from a field in the North Sea. The plugs were subject to estimated effective in situ conditions during measurements. Using an inversion procedure on the data, the Thomsen parameters e and δ were estimated. The degree of anisotropy appeared to correlate with the amount of mica/illite, also enabling a continuous estimate of e and δ vs. depth from clay indicator wireline logs from the same wells where the cores stemmed from. This log-result was subsequently used as an input to migration of walk-away VSP data from the field, employing a multi-layer model with intrinsically anisotropic layers. Inclusion of this anisotropy gave a significantly better fit to the traveltime data, as well as improved imaging of the reflectors when compared to an isotropic migration.