Evolution of small-scale flow barriers in German Rotliegend siliciclastics BENJAMIN BUSCH 1 *, REBECCA WINKLER 1 , KEYVAN OSIVANDI 2 , GEORG NOVER 3 , ALEXANDRA AMANN-HILDENBRAND 4 & CHRISTOPH HILGERS 1 1 Institute of Reservoir-Petrology, EMR Energy and Mineral Resources Group, RWTH Aachen University, Wuellnerstraße 2, 52062 Aachen, Germany 2 RWE DEA AG, Hamburg, Ueberseering 40, 22297 Hamburg, Germany 3 Steinmann-Institute of Geology, Mineralogy und Palaeontology, University Bonn, Meckenheimer Allee 169, 53115 Bonn, Germany 4 Institute of Geology and Geochemistry of Petroleum and Coal, EMR Energy and Mineral Resources Group, RWTH Aachen University, Lochnerstraße 4-20 (House B), 52062 Aachen, Germany *Corresponding author (e-mail: Benjamin.Busch@emr.rwth-aachen.de) Abstract: Many siliciclastic reservoirs contain millimetre scale diagenetic and structural phe nomena affecting fluid flow. We identified three major types of small scale flow barriers in a clastic Rotliegend hydrocarbon reservoir: cataclastic deformation bands; dissolution seams; and bedding parallel cementation. Deformation bands of various orientations were analysed on resistivity image logs and in core material. They are mainly conjugates, and can be used to validate seismically observable faults and infer subseismic faults. Bedding parallel dissolution seams are related to compaction and post date at least one set of deformation bands. Bedding parallel cementation is accumulated in coarser grained layers and depends on the amount of clay coatings. Apparent permeability data related to petrographical image interpretation visualizes the impact of flow barriers on reservoir heterogeneity. Transmissibility multiplier calculations indicate the small efficiency of the studied deformation bands on flow properties in the reservoir. Deformation bands reduce the host rock permeability by a maximum of two orders of magnitude. However, host rock anisotropies are inferred to reduce the permeability by a maximum of four orders of magnitude. The relative timing of these flow barriers, as well as the assessment of reservoir heterogeneities, are the basis for state of the art reservoir prediction modelling. Deformation bands are zones of localized deforma tion in granular media, and are frequently reported from siliciclastic rocks and limestones (e.g. Anto nellini & Aydin 1995; Fossen et al. 2007; Legler & Marchel 2008; Wennberg et al. 2013). Generally, three end members of deformation bands are kine matically classified as shear bands, compaction bands and dilation bands (Fossen et al. 2007). The orientation of the localization plane with respect to the principal stress orientation and the deforma tion band type differs for these three end members (Be ´suelle & Rudnicki 2004, fig. 5.16). Shear local ization forms at low effective stresses, compaction at higher effective stresses and dilation is linked to decreasing effective pressures (Wong et al. 1997; Be ´suelle & Rudnicki 2004). Low porosity and small grain size exert an influence on the phys ical process of strain localization and will result in an increased magnitude of the compactive yield strength (Wong et al. 1997; David et al. 2001; Schultz et al. 2010). The wide range of varying microstructures in deformation bands is reflected by the diverse termi nology, addressing the mineralogical composition (e.g. the incorporation of clay minerals into the deformation band by shearing results in phyllosili cate bands), the kinematic or physical processes of formation (e.g. dilational deformation bands, cata clastic deformation bands and compaction bands) or hybrids of different mechanisms (e.g. shear enhanced compaction bands). Cataclastic deforma tion bands are frequently observed around larger normal faults in soft sediment and weakly lithified rocks, and display the incipient stage of faulting and strain hardening (Antonellini & Aydin 1995; Fossen 2010; Ballas et al. 2012; Soliva et al. 2013). They