Depositional constraints and diagenetic pathways controlling petrophysics of Middle Miocene shallow-water carbonate reservoirs (Leitha limestones), Central Paratethys, Austria-Hungary

摘要

Middle Miocene shallow-water limestones, the so-called Leitha limestones, comprise a widespread Middle Miocene lithological unit of the Central Paratethys Sea. It includes mainly limestones composed of corallinacean algae and other fossil debris and were deposited in shoals of various basins such as the Vienna, Eisenstadt-Sopron and Styrian basins of Austria where they form potential hydrocarbon reservoir rocks. Petrophysical parameters including porosity, permeability, density, P-wave velocity and magnetic susceptibility measurements were performed and evaluated. The sampled sites of Mannersdorf and Wollersdorf quarries and drill-hole Bruckneudorf are located in the Vienna Basin and share the same principal limestones depositional facies that is massive, closely-packed rudstone facies. This facies has low porosities below 10%, low permeability lower than 1.2 mD except one samples at 68.5 mD, high bulk density of dry samples up to 2.64 g/cm(3) and high P-wave velocity up to 6761 m/s. In Mannersdorf, a second facies type of soft porous coarse-grained rudstone shows significantly higher porosity (up to 47%), higher permeability up to 124.3 mD, lower bulk density of dry samples less than 1.8 g/cm(3) and lower P-wave velocity less than 2798 m/s. This latter facies retains primary porosity and secondary porosity enhanced by dissolution. In contrast, the former facies type suffered intensive cementation, which destroyed the primary porosity, and in some cases, subsequent later dissolution and karstification enhanced secondary porosity partly.