Bioturbation and Reservoir Quality: Towards a Genetic Approach

Knaust, Dirk

The process of bioturbation, or the organism/sediment interaction, has a strong impact on reservoir quality and its flow behavior and is capable to either enhance or diminish it. Despite this fact, existing classifications of porosity in carbonates and siliciclastics do not really consider ichnological components as a part, while existing bioturbation-focused classifications are based on the final appearance of burrow-related heterogeneities in the sedimentary rock. A novel approach is made classifying bioturbation-influenced porosity on the basis of the size as well as morphological and compositional features of bioturbate textures and discrete trace fossils. Given the diverse appearance of trace fossils and, consequently, their highly variable influence on the fluid-flow within the sediment, an attempt is made to classify bioturbation-influenced porosity (both, enhancement and diminishing) at different scales and by appreciating the specific burrow nature as a function of the overall behavior of their trace maker. This newly proposed key aims for a better predictability of reservoir quality as an integral part of the reservoir-characterization workflow together with sedimentological and diagenetic analysis. Selected examples of bioturbation-related modifications of rock properties are presented from platform carbonates of the Permian/Triassic Khuff Formation from the South Pars gas field in the Persian Gulf, from shallow-marine Jurassic siliciclastics of the Norwegian North Sea, and from Late Cretaceous deep-marine fan deposits of the Norwegian Sea. These case studies show that the porosity in these reservoirs is significantly impacted by diverse bioturbation, which either results in an enhancement or a diminishing of the reservoir quality. Given a solid understanding of the conditions, burrow-related porosity and permeability are predictable to a certain degree.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013