Aabenraa-1. Zechstein Project. On the Sedimentology and Diagenesis of the Basal Zechstein Carbonate Unit in the Aabenraa-1 Well, Denmark

摘要

The present report is a detailed description and interpretation of the sedimentology and diagenesis of the Lower Zechstein carbonate formation in the Aabenraa-1 well, located close to the break of the Zechstein carbonate platform. Based on well logs and geochemical analyses the carbonate sequence is divided into four units, which are also reflected in the macro and microscopic observations. The carbonate is found to be deposited during the first gentle marine and normal saline transgression and subsequent shallowing, which preceeded the evaporitic phase sensu stricto. During the shallowing of the sea algal oncoidal and stromatolitic mounds were deposited, which were rich in non frame building bryozoans. Recognizeable events of major diagenetic importance are in relative interpreted sequence: stylolitization, leaching, precipitation of anhydrite cement, and thereafter of calcite cement. The mineralogical transformations seem to be related to these events. The important major dolomitisation seems to have taken place after the development of stylolites and the leaching, although a possibility for a very early genesis of the dolomite can not be totally disregarded for two of the units (2 and 4). The porosity and thus the reservoir quality of the rock is largely linked to the phase of leaching. But possibly the porosity is also partly related to the mentioned rather late phase of dolomitisation, as high porosity (and permeability) also coincides with dolomite. The major leaching is interpreted to be genetically related to the uplift and erosion during the period from Late Jurassic to Early Cretaceous. Should this model prove to be more generally valid the exploration effort must be concentrated on platform breaks on locations, which have in their history of burial suffered major intermittend uplift and erosion. EFP-84; 100 refs. (ERA citation 12:003362)