engleski

Distribution of porosity and permeability within the Pontian sandstones in the Western part of Sava depression in relation to their stratigraphyc architecture and palaeotectonic relations

Within the Lower Pontian deposits of the Sava depression, the three genetic stratigraphic sequences are separated, named Poljana, Graberje and Bregi. They are composed of marls intercalated with sandstone bodies containing silty component. These sedimentary bodies are elongated in the NW-SE direction. Analysis of their maximal thickness axes locations allows an interpretation of the translation of depocentre in the south-western and western direction. This is in concordance with the palaeotectonic reconstruction. Namely, it is found out that the zone of the fastest tectonic movements in respect to the preceding Miocene was during Pontian shifted in south-western direction. At the same time, the mean vertical tectonic displacement exhibits a constant increase with the most important jump-like growth in Early Pontian. It is characteristic that the zone of increased tectonic displacement was in Early Pontian translated in the western and south-western direction. The statistic analysis of variables describing the sandstones of the GSS Poljana in the oil fields Okoli and Stružec yielded the following results. The porosity has a roughly normal distribution, and permeabilities the roughly log-normal one (KH, KV and (KH+KV)/2). The correlation indexes between the porosity and permeability depict the good correlation and there is no correlation between the depth and vertical permeability. There is no correlation between the depth and porosity and depth and horizontal permeability at the Stružec field which makes the difference with the Okoli filed where these mentioned correlations are good to mildly indicated. The aforementioned is explained by a non-uniform granulometric composition and by lithologic heterogeneity of shallower layers at the Stružec field.

sandstone; Pontian; Genetic stratigraphyc sequence; Structural evolution; Porosity; Permeability; Sava depression; Croatia

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