Controls on diagenesis of the Triassic Kurrachine Dolomite, Syria

Abstract

The evaluation of major diagenetic processes affecting the main hydrocarbon-producing interval of the Triassic Kurrachine Dolomite, in the central part of Syria, has proved to be of importance in understanding its reservoir characteristics. To describe the paragenetic sequence, core samples from two wells were studied by conventional petrographic analysis. In the first stage, pervasive replacement dolomitisation occurred. The dolomite petrography can be best explained by evaporative dolomitisation in the case of tidal flat facies and by the hypersaline brine reflux model in the case of subtidal facies. During relatively longer periods of subaerial exposure dolocrete sequences were developed. Dolomitisation of subtidal sediments in a more open-marine setting was completed during further burial by rising temperature. As a result, pervasively dolomitised rocks, with minor intercrystalline porosity in subtidal deposits and supposedly in dolocretes, were formed. In the deep burial realm, solution seams and stylolites acted as conduits for migrating hydrocarbon. Overmature hydrocarbon was observed as insoluble residue. Following fracturing and leaching by sulphate-bearing warm fluids, significant vuggy porosity was created but was subsequently occluded by precipitated anhydrite cement. The effective vuggy and fracture porosity of the Kurrachine Dolomite was created by latest stage leaching, which was controlled by the previous deep burial diagenetic processes and fracturing. The selective leaching, on the evidence of dissolution of anhydrite cement, improved the reservoir potential. Taken all together, the Kurrachine Dolomite exhibits evidence of important porosity development in burial conditions. Accordingly, the analysed core porosity and permeability data within the formation varies by location.