Factors controlling the impact of deformation bands on the petrophysical properties of the Upper Rotliegend sandstones (Southern Permian Basin, Poland)

Abstract

The Upper Rotliegend aeolian and fluvial sandstones in the Southern Permian Basin of western Poland reveal an abundance of deformation bands. Well core and thin section analyses supplemented with field-emission electron microscope analysis, as well as porosity and permeability measurements were performed on 100 samples from 12 wells. This enabled the integration of the distribution and composition of the host sandstones with types of deformation bands, along with changes of band petrophysical properties across depths ranging from 1500 m to 4900 m. The main factors controlling the petrophysical properties of sandstones and deformation bands include: sandstone composition, texture and sorting, degree of cementation (quartz, clay minerals, anhydrite, carbonates) during diagenesis, and burial depth. The permeability of deformation bands decreased up to 3 orders of magnitude in relation to the host sandstones. The permeability contrast between the sandstones and the deformation bands is the highest at shallow depths, and decreases with the depth and the degree of cementation and compaction of the host sandstones. The degree of permeability reduction in the analysed samples is consistent with the data reported in other areas of the Southern Permian Basin, although the analysed data show slightly lower porosity and permeability compared to analogous regions in the western part of the basin. Therefore, this analysis provides data representative of the Polish part of the basin and may contribute to more accurate flow modelling, as deformation bands can act as baffles to fluid flow and thus influence the structure and quality of the Upper Rotliegend reservoir.