Monitoring changes in velocity and Q using non-physical arrivals in seismic interferometry

Abstract

Application of seismic interferometry to records from receivers at the Earth’s surface from sources in wells retrieves the reflection response measured at the receivers as if from virtual sources located also at the surface. When the wavefields experience intrinsic losses during propagation, non-physical arrivals (ghosts) would appear in the retrieved result. These ghosts appear due to waves that reflect inside a subsurface layer. Thus, a ghost contains information about the seismic properties of the specific layer. We show how such ghosts can be used to monitor layer-specific changes in the velocity and intrinsic losses in the subsurface. We show how to identify the ghosts using numerical-modelling results from a vertical well, and how to estimate the layer-specific velocity and quality-factor changes using numerical-modelling results from a horizontal well as well as ultrasonic S-wave laboratory data.