Determining the Limitations to Deep Reservoir Caprock Fracture Characterisation Using AVOA Analysis

This study uses azimuthal AVO to assess the limitations to detecting and characterising fractures in a 150m thick caprock of a 3200m deep saline reservoir for CO2 storage. Simple and full-waveform synthetic surface reflection seismic data were generated using ATRAK and Wave Unix, respectively, to provide varying levels of signal to noise ratios for the analysis. Nine models with varying noise content, structural complexities and fracture intensity were evaluated. The outcomes of the investigation are that: fracture intensity must be strong to be observable; a layer-stripping mechanism is necessary to reduce the effect of overlaying layers; changes in anisotropy due to changes in fracture intensity can be measured; the direction of anisotropy can be recovered but not its magnitude. The influence of large velocity contrasts is the key uncertainty in the estimation of anisotropy in this geological setting.