The diagenetic history of Oligocene-Miocene sandstones of the Austrian north Alpine foreland basin |
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| Institution: | 1. University of Wroc?aw, Institute of Geological Sciences, Pl. Maksa Borna 9, 50-204 Wroc?aw, Poland;2. Polish Geological Institute–National Research Institute, Lower Silesian Branch, Al. Jaworowa 19, 53-122 Wroc?aw, Poland;1. University of Kentucky, Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511, United States;2. Department of Geology and Geography, Georgia Southern University, Statesboro, GA 30460, United States;1. Delft University of Technology, Faculty of Civil Engineering and Geosciences, Department of Geoscience and Engineering, Stevinweg 1, NL-2628 CN Delft, The Netherlands;2. University of Leuven, Faculty of Earth and Environmental Sciences, Department of Geology, Celestijnenlaan 200E, 3001 Heverlee, Belgium |
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| Abstract: | Diagenesis is an essential tool to reconstruct the development of reservoir rocks. Diagenetic processes - precipitation and dissolution - have an influence on pore space. The present paper aims to study the diagenetic history of deep-marine sandstones of the Austrian Alpine Foreland Basin. To reach that goal, sediment petrology and diagenetic features of more than 110 sandstone samples from water- and gas-bearing sections from gas fields within the Oligocene-Miocene Puchkirchen Group and Hall Formation has been investigated. Special emphasis was put on samples in the vicinity of the gas-water contact (GWC). The sediment petrography of sandstones of Puchkirchen Group and Hall Formation is similar; hence their diagenesis proceeded the same way. In fact, primary mineralogy was controlled by paleo-geography with increasing transport distance and diverse detrital input.Sediment petrographically, investigated sandstones from the water-bearing horizon seemed quite comparable to the gas-bearing sediments. In general, they can be classified as feldspatic litharenites to litharenites and display porosities of up to 30% and permeabilities of up to 1300 mD. The carbon and oxygen isotopic composition of bulk carbonate cements from these sandstones range from?3.8 to +2.2 and from ?7.5 to +0.2‰ VPDB]. However, near the Gas-Water Contact (GWC) a horizon with low porosities (<3%) and permeabilities (<0.1 mD) is present. This zone is completely cemented with calcite, which has a blocky/homogenous morphology. A slight, but significant negative shift in δ18O isotopy (?2.5‰) is evident.During early diagenesis the first carbonate generations formed. First a fibrous calcite and afterwards a micritic calcite precipitated. Further siliciclastic minerals, such as quartz and feldspar (K-feldspar and minor plagioclase), exhibit corroded grains. Occasionally, clay minerals (illite; smectite, chlorite) formed as rims around detrital grains. Late diagenesis is indicated by the formation of a low permeable zone at the GWC. |
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| Keywords: | North Alpine Foreland Basin Diagenesis Gas-water contact Reservoir rock Microbial gas generation Carbonate cement |
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