Seismic Attribute Expression of Differential Compaction
Chopra, Satinder; Marfurt, Kurt
Differential compaction is routinely used by seismic interpreters to map features of interest such as identifying carbonate buildups, recognizing sand fans in shallow as well as deep waters, or in seismic geomorphological-based interpretation of fluvial deltaic systems. Compaction features over laccoliths and dykes are recognized as a means of generating fractures in overlying sediments. Seismic attributes such as coherence and curvature are used for mapping structural features such as faults, folds and flexures, as well as in mapping discontinuities that arise at channel edges. In this work we show modern 3-D examples of positive relief, sand-filled channel features in a shale matrix and negative-relief, compacted Winnipegosis carbonate buildups in a salt matrix in the Western Canadian Sedimentary Basin.
By understanding the depositional environment, differential compaction can serve as a lithologic indicator that can be incorporated with other ‘soft' measurements such as reflection amplitude anomalies, AVO anomalies, and velocity pull-ups in a risk-analysis based prospect evaluation workflow. Positive curvature anomalies over channel features indicate that these channels are filled with a lithology that is less compactable than the surrounding matrix, indicating the presence of sand. Negative curvature anomalies over channel features are more problematic. If the channels are in near-shore environment and have been filled by rising sea level, there is a very high probability that they are filled with shale, indicating that sand should be found in the surrounding, less-compacted point bars and levees that often express a positive curvature anomaly. In general, incised channels may be filled with a mix of lithologies resulting from multiple stages of incisement and fill. If the topography has been exhumed, the surrounding material may already have been compacted, reducing the differential compaction anomaly associated with a sand-filled channel.
Carbonate buildups buried in shale will give rise to structural highs and positive curvature anomalies along the shallower, more easily picked horizons. Carbonate buildups buried in salt, such as our Winnepegosis reef example, will appear as structural lows, giving rise to a negative curvature anomaly. Such compacted structural reef cores may have lost much of their original porosity, resulting in donut-shaped features where the structurally high rims preserve much of their original porosity.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013