Petrophysical, facies and mineralogical-geochemical investigations of Rotliegend sandstones from the Altmark natural gas field in Central Germany

Abstract In this collaborative study of the Universities Jena and Clausthal and the GDF SUEZ E&P Deutschland within the framework of the R&D program “CLEAN“Rotliegend sandstones of the Altmark natural gas field were investigated by sedimentological, mineralogical, geochemical and petrophysical means. In compilating the gained results potential correlations of specific rock attributes should be evaluated, to support the implementation of a planned EGR project. Therefore, as some kind of natural analogue for potential fluid-rock interactions during EGR, varied colored and altered sandstone types, which are most likely affected by such processes in the past, were analyzed. Preliminary results confirm subtle to major differences in mineralogical and geochemical rock composition, as well as petrophysical differences, due to rock colors and litho- and diagenetic facies types. All the rocks are characterized by early diagenetic sebkha/playa calcite and anhydrite cementation and varying amounts of hematitic-clayey clast rimming cutans. Varying degrees of cement dissolution and (partial) cutan recrystallization (?) during diagenesis resulted in different rock porosities and permeabilities. Highest porosity and permeability is typical for aeolian type sandstones and altered (bleached) rock types. Analysis of irreducible water saturation suggests that during injection large pressure gradients in the near-wellbore area are likely. Thus effects of mobilization of the gas and the water phase in the near-wellbore zone due to high pressure gradients and CO 2 induced mineralogical dissolution effects could facilitate clean-up processes and increase the injectivity of CO 2 injection wells in the Altmark.