Reservoir and aquifer characterization of fluvial architectural elements: Stubensandstein, Upper Triassic, southwest Germany

This paper aims at a quantitative sedimentological and petrophysical charac terization of a terminal alluvial plain system exemplified by the Stubensan dstein, South German Keuper Basin. The study follows the outcrop-analogue a pproach, where information derived from outcrops is collected in order to e nhance interpretation of comparable subsurface successions. Quantitative da ta on sandbody geometries, porosities and permeabilities are presented in o rder to constrain modelling of subsurface sandbodies and permeability barri ers. For sedimentological characterization the method of architectural elem ent analysis (Miall, A.D., 1996. The Geology of Fluvial Deposits. Springer, Berlin) was used, and modified to include poroperm facies. A special photo -technique with a precise theodolite survey was developed to create optical ly corrected photomosaics for outcrop wall maps from up to 20,000 m(2) larg e outcrops. Nine architectural elements have been classified and quantified . Bedload, mixed-load and suspended-load channel fills are separated. The p etrophysical characterization of the architectural elements integrated poro sity and permeability measurements of core-plugs with gamma-ray measurement s along representative sections. It could be demonstrated, that certain arc hitectural elements show a characteristic poroperm facies. Four scales of s edimentary cycles have been recognized in the Stubensandstein. Cyclic sedim entation causes changing lithofacies patterns within the architectural elem ents, depending on their position in the sedimentary cycle. Stratigraphic p osition exerts only some, paleogeographic position exerts significant influ ence on porosity and permeability of the sandbodies. The highest poroperm v alues were found in proximal areas of the alluvial plain and in middle part s within sedimentary macrocycles. The strong internal heterogeneity on the alluvial plain system is important for its reservoir and aquifer characteri stics. Compartments of bedload channel sandstones in medial positions of a stratigraphic cycle represent very good reservoirs or aquifers. The seals o r aquicludes are formed by extensive floodplain claystones, lacustrine sedi ments, paleosols, and suspended-load deposits. Strongly cemented zones of s andstones represent aquitards. (C) 1999 Elsevier Science B.V. All rights re served.