Sequence Stratigraphy Integrated with Petrophysical Rock Typing: A Case Study from Carbonate Reservoir Analogs (Muschelkalk, Triassic, German Basin)

Braun, Sascha¹, Thomas Aigner² (1) Wietze Laboratory, Wietze, Germany (2) University of Tuebingen, Tuebingen, Germany

Outcrop analog studies provide quantitative data on reservoir bodies as input for static reservoir modelling. This study reports on shelly versus oolitic carbonate shoal bodies. These were deposited on a carbonate ramp of the intracratonic Muschelkalk basin in Central Europe, which in several ways provides analogs to hydrocarbon reservoirs in the Middle East. In the Muschelkalk analogs, shoal reservoirs occur in the top parts of meter-scale shal-lowing-up cycles. These stack vertically to larger-scale transgressive and regressive trends, building multiple reservoir storeys. Within the larger-scale regression shoal bodies system­atically increase in abundance, size and thickness. Individual reservoir bodies are up to 18 x 8 km in extend and up to 2 m thick. The shoal bodies during the larger-scale regression tend to be rich in oolites, while those during larger-scale transgression are dominated by molluscan shells. Lithofacies types do not show consistent poroperm patterns but scatter widely. However, focussing on pore types and using the petrophysical rock type approach leads to better defined fields in poroperm crossplots. The oolitic shoals are dominated by separate-vug pores providing little permeability (k < 5 mD). In contrast, the shelly shoals show primary interparticle porosity in addition to separate-vug, leading to better permeabil­ities (k(h) = 45-82 mD). Thus the best reservoir quality occurs during large-scale transgres­sion due to the predominance of highly permeable shelly shoals. Regional high resolution sequence stratigraphy determined the reservoir distribution, i.e. the architecture and geom­etry of the shoal bodies. However, only integration with petrophysical rock typing provided information on reservoir quality.