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Why Comparing Ichnofabrics Does Provide High Resolution Information Compatible with Reservoir Scale Studies?

Gerard, Jean 1; Bromley, Richard 2
1 Discplinas Geologicas, Repsol Exploacion SA, Madrid, Spain.
2 Geological Museum, Geological Museum 5-7 Oester Volgade, Copenhagen, Denmark.

Ichnology provides useful information on the environmental conditions that prevailed during or shortly after sediment deposition. As such, recognition and interpretation of trace fossils are now integrated in advanced sedimentological core studies. Like most other laboratory or field techniques, ichnology should not be used as a stand-alone tool. Ichnofabric information is best used in the full context of the sedimentary framework. Only then can ichnology provide detailed environmental information that can be related to depositional processes, relative palaeobathymetry and sequence stratigraphy.

The use of “ichnofabrics” has increased steadily since the ichnofabric concept was first developped by Bromley and Ekdale in 1984: “Ichnofabrics: all aspects of the texture and internal structure of a sediment that result from bioturbation at all scales”.

Ichnofabrics allow not only large third-order cycle recognition, but can also identify and correlate higher-frequency cycles by comparing the ichnofabric cycles and their vertical stacking. Sequence stratigraphers can extract shallowing-upward and deepening-upward trends from the recurring ichnofabric patterns, which supply reliable constraints for interpreting and correlating all the bounding surfaces and patterns between wells. The level of resolution supplied by ichnofabrics thereby becomes more compatible and comparable to reservoir characterization level.

From a reservoir viewpoint, the impact of bioturbation on early diagenetic fluid flow is becoming increasingly highlighted, as it may ultimately control micro-scale heterogeneity by enhancing (leaching) or deteriorating (mixing mud and sand or cementing) the reservoir quality of the sediment during burial history. Ichnofabrics when correlated to rock petrophysical characteristics can help break the stratigraphy of a reservoir section into a series of rock types having different reservoir potential.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009