3C Deghosting for Refraction Time-lapse Monitoring

Refraction time-lapse monitoring provides affordable areal measurements of reservoir changes using waves that travel from sources along a fast layer underlying the reservoir. When the waves exit the fast layer, they travel through the reservoir and propagate to the receivers, with corresponding arrival times depending on the state of the reservoir. For thermal EOR, changes in the reservoir can be observed and interpreted from changes in these arrival times. Buried receivers benefit onshore seismic acquisition, partly because statics problems are less severe and because some decoupling from surface waves can be expected. Unfortunately, the statics problem is often just replaced by another problem – surface ghosting with strong near-surface effects. For refraction data, which is lower fold, ghost removal can be even more important than for conventional seismic data. At Peace River in Alberta, Canada, deghosting was carried out using a 3C wave field separation technique used in earlier publications by one of us (De Meersman) to analyse near surface attenuation of shear waves. We demonstrate that the method significantly improves the time shift measurements and demonstrate its use in a processing workflow resulting in an interpretable areal time-shift map for a new refraction time-lapse data set recorded in 2010/2011