The Three Dimensional Petrophysical Structure of Deformation Bands within high Porosity Sandstones

Thomas D. Seers
School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, United Kingdom
[email protected]

Strain within high porosity sandstones is commonly localized within deformation bands: narrow tabular zones of disaggregated, rotated and/or crushed grains, formed under spectra of failure modes. Whilst enhancement of host rock permeability has been recorded from dilatant examples, petrophysical degradation is more characteristic of deformation band formation. The postulated influence on reservoir production leading from this observation has motivated numerous investigations into the petrophysical properties of deformation bands, with most attempting to correlate microstructural observations with permeameter measurements.

However, the use of bulk measurements which represent the amalgamation of host rock and deformation band hydraulic conductivity is highly undesirable, introducing unquantifiable uncertainties into the analysis. Moreover, such measurements cannot resolve the spatial variability in petrophysical properties observed in deformation bands, which are critical to understanding flow mediating behaviour. Whilst preferable to bulk measurements, 2D image analysis methods (e.g. based on the Kozeny-Carmen relation) using thin section micrographs may prove inaccurate where grain alignment regulates flow pathways.

We propose that microtomographic imaging of fluid diffusion coupled with pore-scale flow simulations could provide the capability to characterize the 3D petrophysical structure of sandstone hosted deformation bands. Whilst microtomography has previously been used to image field and synthetic examples these studies focussed upon characterizing gross morphology without considering pore-scale flow. And whilst the potential of microtomographic imaging and flow modelling to resolve pore heterogeneity within strain localization features has previously been recognised, such a schema has hitherto, yet to be implemented.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects