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Abstract: Prediction and Development of Zechstein 2 Carbonate Reservoirs in the West-Emsland Area, Upper Permian, Northwest Germany

Werner Dauben, Christian Strohmenger

The integration of facies, well log, and seismic data within a sequence stratigraphic framework of the Basal Zechstein led to a 3-D model of the reservoir facies distribution. The model improved the reconstruction of the depositional history with respect to preexisting topography, eustatic sea-level changes, and structural setting.

The subdivision of the Zechstein 2 carbonate (Ca2) into 25 subfacies types, based on detailed core descriptions, enables the localization of depositional environments (supra-, inter-, and shallow subtidal for the platform facies; upper, middle, lower slope and basin for the deeper-marine facies).

The Ca2 represents a complete 3rd-order sequence. Vertical subfacies successions and their specific gamma-ray and sonic-log responses allow the identification of systems tracts and shallowing upward parasequences within the Ca2. The lateral extent of porous zones has been mapped by integrating parasequence sets and petrophysical data in chronostratigraphic well-log correlations.

Thickness relationships among the Ca2, the underlying Werra Anhydrite (A1), and the overlying Basal Anhydrite (A2) and the Staßfurt Salt (Na2) serve as an additional prediction tool of Ca2-facies distribution due to abrupt thickness changes of these lithologic units in a predominant prograding platform-to-basin-architecture. The most porous, dolomitic Ca2 facies were deposited as late-highstand and lowstand-wedge shoal and bar complexes at the end of Ca2 time, and lie between the A1- and the A2-platform margins.

3-D seismic interpretations coincide with the high-resolution correlations, delineate the limiting margins, and additionally detect syndepositional tectonics, which caused anomalies in Ca2 thickness and facies distribution. High seismic amplitudes at the base of the Ca2 and low impedance indicate good reservoir quality. However, variations in Ca2 thickness, lithology (grade of anhydritization) and pore content, render the interpretations of attribute anomalies difficult.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France