S-waves and the near surface: A time-lapse study of S-wave velocity and attenuation in the weathering layer of an Alberta heavy oil field

Abstract

This study used data from a three-month continuous reservoir monitoring experiment in Peace River, Alberta, Canada to measure spatial and temporal variations in near-surface S-wave velocity (VS) and attenuation (QS) in the weathering layer. The permanently buried sources generate a strong refracted S-wave that was recorded on buried 3C receivers. A method to perform receiver-side up-down separation and extract primary and ghost S-wavefields is presented. These wavefields are then used to measure near-surface VS and QS for the near-surface layer above the buried receivers, which is the top 12 m in this case. The measured VS values range between 180 and 220 m/s and QS values between 8 and 22. Maps of VS and QS show a robust correlation (low VS with low QS) and a clear spatial variation that can be associated with soil type. Both properties increase slowly over a three-month period in one section of the survey area while remaining constant in another. The cumulative increase in VS and QS is 10%.