engleski

Distribution of Porosity and Permeability within the Pontian Sandstones in the Western Part of Sava Depression in Relation to their Stratigraphic Architecture, Palaeotectonism and Production of Oil and Gas

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 shallower reservoirs have a significant reduction of porosity with increase of depth, the deeper ones show a very mild correlation. The distribution of vertical and horizontal permeability in relation to the depth increase shows the same relations. The porosity – permeability plots illustrate the gradual increase of the average permeability with the porosity, which is even more expressed in the deeply situated reservoir rocks. The aforementioned is explained by a higher level of granulometric and lithologic heterogenity of shallower layers. As a result of the favourable petrophysical characteristics of the studied strata and adequate management of displacement process, the actually obtained recovery reached the prognosed values.

sandstone; Pontian; genetic stratigraphic sequence; palaeotectonism; structural evolution; porosity; permeability; hydrocarbon production; Sava depression; Croatia

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