Multiple-scale facies and reservoir quality variations within a dolomite body – Outcrop analog study from the Middle Triassic, SW German Basin

This study focuses on a porous dolomite body in the proximal part of an epeiric carbonate ramp (Triassic Muschelkalk, South German Basin), analogous to hydrocarbon-bearing dolomite reservoirs in the Middle East (e.g. Khuff and Arab Formations). lomite body is made up of shoal, lagoonal and peritidal facies types and is built by a three-fold hierarchy of cycles (3rd-order to 5th-order). The best reservoir quality occurs in finely crystalline lagoonal dolo-mudstones (mean: K = 37.8 mD; φ = 20.2%) with micro-intercrystalline and vuggy porosity. Coarsely crystalline, shoal-related dolo-grainstones show variable reservoir potential (mean: K = 30.1 mD; φ = 4.4%) due to late diagenetic modification. Reservoir quality significantly decreases in the non-dolomitized foreshoal section (mean: K = 4.5 mD; φ = 3.6%). Stratigraphically, the most porous dolomite occurs in the upper regressive portion of the 3rd-order cycle. Reservoir quality progressively decreases towards the limy bottom of the section. p mapping showed high lateral continuity for the distribution of facies types and poroperm values on the scale of several 10s of meters. Within correlated 5th-order cycles, considerable facies and poroperm heterogeneity is already observed on the 100s of meters-scale. On a 1000s of meters-scale, the facies and lithology distribution is controlled by the geometry of a gently inclined carbonate ramp. During regression, a progradational pattern is recognized, marked by a basinward migration of backshoal facies and a down-dip decrease of dolomite body thickness. ogy, facies and poroperm data from outcrops and cores were used for 3D-modeling with the software Petrel. The modeled variations in the poroperm distribution are consistent with the degree of heterogeneity expected for a combination of laterally persistent lithology and highly variable facies. s of this study may help to better understand the reservoir heterogeneity of inner ramp dolomite bodies and can be applied to improve characterization and modeling of similar dolomite reservoirs.