MINERALOGICAL INVESTIGATIONS ON LOWER TRIASSIC CLASTIC SEDIMENTS. OUTCROP STUDIES AS A TOOL TO REFINE THE SEAL CHARACTERISTICS

The uppermost part of the lower Triassic „Buntsandstein“ is termed Röt–Folge. The Karsdorf-Quarry located in north-eastern Germany is the type-section of the Karsdorf-subformation within the Röt interval. Since the Röt-Folge can be regarded as a potential seal-formation in CCS technology, we aim to refine the knowledge of the Röt lithology and its petrophysical properties. Therefore sediments taken 9 samples from the Karsdorf Quarry have been investigated for their mineralogy, grain size distribution as well as their petrophysical parameters.

The finely grained clastic sediments are mostly reddish to brownish in colour. The majority of the 40 m thick succession is thin bedded and in the lower part of the Quarry the beds are irregular cut by gypsum layers. The so called “Doppelquarzit” bed as the most significant bed has been used to reconstruct the stratigraphic position of the whole succession and the two prominent calcareous sandstone-beds therein are the coarsest beds in the section.

To investigate the interaction between potential seal-rocks and a CO2-rich fluid, the selected rocks will be altered under simulated “in-situ” conditions in a laboratory autoclave system. For these experiments synthetic formation brine has been used. Due to the high temperature in the autoclave CO₂ will be in supercritical state throughout the experiment. The fluids and rock samples remain in the autoclave system for about two weeks and are investigated thereafter for possible changes due to the exposure to CO₂ and brine.

Here we show first results on rock behaviour from the analyses of the mostly clayey and siltey sediments together with the results on (clay) mineralogy, XRF analyses as well as grain size analysis that has been used to determine the petrophysical parameters besides direct measurements before and after treatment. Initial porosities range between 0.94 and 15.01 % . with a carbonate content between 1.8 and 41.3 % by weight.