High resolution petrophysical measurements of deformation bands in sandstones

Abstract

Sub-seismic scale deformation bands have an impact on production from hydrocarbon reservoirs since they have dramatically reduced porosity and permeability. These changes are commonly quantified using relatively low-resolution techniques, which invite host rock bias in measurement and inevitably underestimate the potential of these structures as fluid barriers. High-resolution petrophysical measurement within these discontinuities and the characterization of their variable microstructures are therefore critical in their incorporation into advanced reservoir simulation models. These have been carried out using pressure decay probe permeametry (PDPK) of slabbed sandstones containing a range of deformation band types combined with image analysis porosimetry of optical thin sections containing deformation bands. The higher resolution techniques show that much greater differences between host rock and deformation band petrophysical properties exist than when measured using conventional techniques. Cataclastic deformation bands in clean, highly porous sandstones have experienced the greatest reductions in sandstones have experienced the greatest reductions in sorting relative to their host. There is less contrast in these properties between clay-rich deformation bands and clay-rich host sandstones. This is due to an already low depositional porosity hence giving little opportunity to reduce the porosity further. The influence of lithology upon the formation of deformation bands does not apply to the same extent to cemented deformation bands, the cement of which is affective in modifying sandstones with high depositional porosity and permeability.