Preliminary processing for Chaparral-Farnsworth VSP data set with focus on attenuation

Scott Keating, Kristopher A. H. Innanen, Scott Leaney

In this report the Chaparral Farnsworth VSP data was investigated, with the aims of establishing an attenuation profile and identifying difficulties that may arise if anacoustic FWI were applied to the data. Q estimates were generated using both the spectral ratio method and the centroid frequency shift method. These yielded consistent results, prominently featuring nonphysical negative Q. Scattering effects were investigated as a potential cause for this error. Synthetic VSP data generated using the well logs demonstrated that scattering effects do provide effective negative Q forcing in the Q estimation methods, but not in the correct locations or to the necessary extent to cause the apparent negative Q in the measured data. Scattering effects on a smaller scale than the well log sampling could not be discarded as a potential cause for this behaviour however. A capacity to be able to account for both Q induced frequency shifts and sub seismic resolution scattering induced shifts is identified as a desirable property in any anacoustic FWI to be applied to this data.