Bridging the Gap from Hand-Specimen to Basin: Understanding the Scalar Impacts of Bioturbation on Reservoir Quality

Callow, Richard; McIlroy, Duncan; Herringshaw, Liam

Bioturbation is known to affect reservoir quality through processes such as grain sorting, grain mixing, sediment packing, pipework formation and bioinfiltration. While hand specimen- and bed-scale studies have proved invaluable in assessing the impact of different trace fossils on porosity and permeability, it is currently less clear how these local effects can be extrapolated to bedset, parasequence, formation or basinal scales in three dimensions. Using a number of case studies of well-known, common trace fossils that represent contrasting behavioural styles (Phycosiphon, Ophiomorpha, Skolithos and Scolicia), this presentation will discuss the potential for upscaling detailed analyses into larger models that can be applied to reservoir characterization in slope, shelf and shoreface environments. The effects of individual burrows on the near-burrow environment are always important, but the magnitude is dependent upon the behaviour of the tracemakers and the nature of the substrate. In fine-grained, diffusion-dominated successions, for example, grain-selective ichnotaxa such as Phycosiphon can enhance reservoir connectivity at all scales. In coarser grained, advection-dominated successions, some trace fossils can reduce reservoir quality on a bed-scale, while enhancing connectivity on bed-set and parasequence scales. Conversely, others can increase local reservoir quality while having a detrimental effect on broader reservoir quality. Realistic, high-resolution models of composite ichnofabric development over inter-well scales are key to the accurate prediction of variations in reservoir quality resulting from bioturbation. Accurate mapping of ichnofabrics and an understanding of facies controls, lateral patchiness, and intensity are of particular importance. By producing detailed models of the effects of individual ichnotaxa at multiple scales, and by understanding the environmental distributions of these ichnotaxa, it may be possible to produce reliable models predicting the reservoir-scale effects of bioturbation.

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