ИСТИНА

Otway CO2CRC project focuses on the development of effective technologies for capture, storage and monitoring of carbon dioxide (CO2) injections into the subsurface. In this study, we investigate the phenomenon of seismic attenuation at the Otway site. We consider a set of nine zero-offset VSP (ZVSP) datasets from the four wells located within the radius of 1 km from each other. The redundancy of the available data provides a unique opportunity to compare and evaluate the reliability of the attenuation estimates. We compare conventional Amplitude Decay (AD) and Centroid Frequency Shift (CFS) methods versus a recently reported 1D waveform inversion (WI) that allows one to separate the effect of layer-induced scattering on Q-estimates (Q being a measure of attenuation). We demonstrate that WI gives more robust estimates than AD and CFS. However, results of all of the methods may be distorted by the presence of non-horizontal features such as faults. The obtained Q-models for the four boreholes are broadly consistent with each other. They reveal a pronounced seismic attenuation (1/Q > 0.02) for the shaley formations. The thin CO2 plume (< 30 m) does not produce a noticeable effect on attenuation estimates.