Channel-body basal scours: Observations from 3D seismic and importance for subsurface reservoir connectivity

Scouring at the base of channel bodies plays a significant role in enhancing connectivity of sandstone reservoirs. Investigation of high-resolution 3D seismic data from a fluvial and deep-water channel system illuminates the location and spacing of channel-body basal scours and possible controls. Scours in both East Breaks upper fan (Quaternary) and Iron River fluvial channel-bodies (Cretaceous) are comparable in scale, with a deviation of up to 10 m scour depth relative to the average channel-body basal depth.Substrate lithology, as documented by draping well-calibrated seismic response onto 3D channel body basal surfaces, does not appear to be a major influence on scour location or depth. In the datasets examined, channel-body basal scour locations appear to be most influenced by changes in channel orientation, with outer bends being particularly prone to scouring, even in channels that are not highly sinuous.Scaling relationships between scour spacing and channel width observed in modern fluvial systems are further tested against these high-resolution datasets and published Miocene subsurface deep-water reservoir maps but results are mixed, with a consistent over-prediction of scour spacing. This may reflect difficulties in accurately determining channel bank full width in confined deep-water channel complex systems.Observations from an ancillary 4D seismic dataset show that over 30% of the identified scour areas exhibit attribute anomalies calibrated with water saturation changes between the baseline and monitor surveys (about 3 years) and thus indicate production-induced fluid movement through these features. This underlines the importance of scours as connection points between fluid compartments and the significance of observations of scour location and spacing made here from high-resolution 3D and ancillary 4D seismic data.

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► High-resolution 3D seismic data illuminates channel-base scours that often connect subsurface reservoir compartments.
► Possible controls considered are slope gradient, substrate lithology, and channel geometry.
► Neither gradient nor substrate lithology greatly influence scour depth or location in the datasets examined.
► Basal scour locations are most influenced by changes in channel geometry, with outer bends prone to formation of deep scours.
► Measured ratios of scour spacing/channel width are often less than observed previously for smaller alluvial channels.