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The Impact of Dedolomitization on Reservoir Quality of the Upper Permian Zechstein 2 Carbonate, NW Germany
The Zechstein-2-Carbonate (Ca2), one of the most prolific gas reservoirs in northwestern Germany, shows a textbook correlation between petrophysical properties and mineralogy. Matrix porosity and permeability is high in dolomite and low in calcite. Petrographic analyses of c. 300 thin sections show that around 70% of all calcite observed corresponds to dedolomite, replacing diagenetically early dolomite and significantly reducing average porosity (e.g. by more than 10% in a dedolomitized oolite grainstone bar). The 3D distribution of both minerals on a prospect-scale and between wells is often challenging to predict. We evaluate statistically the porosity, permeability, lithofacies and mineralogy data from core (n = 51 wells) using box plots for the northern and southern Zechstein gas fairway. In a next step these observation-based rules and diagenetic patterns will be conceptually integrated into a 3D stratigraphic block model, enabling to develop a conceptual model for the paleo-hydrogeologic pathways of the dedolomitizing fluids. This rather simple processing of large statistical higher level datasets calibrated by carbonate petrography easily enables the integration of new well data and a more accurate constraint on the uncertainty range of predicted gas volumes. The project will be conducted in cooperation with Exxon Mobil Production GmbH, Germany.
Associated researchers: Lars Reuning