Viscoacoustic-Waveform Inversion with the Local Frequency Shift: Application to the Blue Mountain Geothermal Field

Abstract

Accurate estimate of seismic attenuation is valuable for geothermal reservoir characterization. Seismic waves traveling through geothermal reservoirs result in amplitude loss and velocity dispersion. Waveform inversion has the potential to reconstruct subsurface attenuation distributions. However, a reliable estimate of an attenuation model is difficult because the amplitudes of seismic data are affected by other factors such as scattering or changes in impedance in addition to attenuation. We develop a novel viscoacoustic waveform inversion method for addressing the difficulties in attenuation inversion. To mitigate the effect of amplitude distortion, we analyze the local peak/centroid-frequency shifts using short-time Fourier transform, and then use the frequency shifts as a misfit function in the waveform inversion to invert for the attenuation model. We apply the method to 2D surface seismic data acquired at the Blue Mountain geothermal field, and our results show that the geothermal reservoir exhibits higher attenuation than the surrounding regions.