PORES, CEMENTATION AND STRUCTURE OF EXPOSED SHALE GAS ROCKS IN GERMANY – FIRST RESULTS

Lower Jurassic and Carboniferous marine black shales may be considered as good unconventional reservoirs. Our focus is on three units in quarries and natural outcrops, which expose parts of the strata and may act as analogs for deep seated reservoirs. The approximately 30m thick Lower Jurassic Toarcian Posidonia Shale in NW-Germany is dominated by fine-grained, thin-layered shale including cemented geode layers. The Lower Carboniferous 8-25m thick Alum Shale is dominated by a folded, faulted black slate intercalated by coarser grained pyritic layers. The Upper Carboniferous Black Shale from W-Germany is characterized by concretions in black shale. Gamma Ray spectra can be used to distinguish the major sets of geodes and shale, showing a trend to lower values in the geode layers, but being consistent in the margin of error in the shale sets. The different shales show different spectra and a high content of uranium and thorium in Alum Shales. Gamma Ray trends can also be recognized in the mechanical stratigraphy, showing a maximum of 12 MPa of uniaxial compressive strength parallel to bedding. The structural features of the outcrops mainly comprise closely spaced open joints, which were created post-diagenetic / concretion. Fracture corridors accumulate around faults in the Alum Shale. Previous studies showed that the TOC content in the shales ranges from 5-15% (Posidonia Shale, North Germany) and from 0.5-10% (Carboniferous shales, Rhenish Massif), which is in accordance with our high resolution study. Our data will be integrated with high-resolution images of the nanoscale porosity to distinguish the variations of different shale gas rocks.