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  • Author: Adam Zubrzycki x
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Stanisław Dubiel, Adam Zubrzycki, Czesław Rybicki and Michał Maruta

Abstract

In the south part of the Carpathian Foredeep basement, between Bochnia and Ropczyce, the Upper Jurassic (Oxfordian, Kimmeridian and Tithonian) carbonate complex plays important role as a hydrocarbon bearing formation. It consists of shallow marine carbonates deposited in environments of the outer carbonate ramp as reef limestones (dolomites), microbial - sponge or coral biostromes and marly or micrite limestones as well. The inner pore space system of these rocks was affected by different diagenetic processes as calcite cementation, dissolution, dolomitization and most probably by tectonic fracturing as well. These phenomena have modified pore space systems within limestone / dolomite series forming more or less developed reservoir zones (horizons). According to the interpretation of DST results (analysis of pressure build up curves by log - log method) for 11 intervals (marked out previously by well logging due to porosity increase readings) within the Upper Jurassic formation 3 types of pore/fracture space systems were distinguished:

- type I - fracture - vuggy porosity system in which fractures connecting voids and vugs within organogenic carbonates are of great importance for medium flow;

- type II - vuggy - fracture porosity system where a pore space consists of weak connected voids and intergranular/intercrystalline pores with minor influence of fractures;

- type III - cavern porosity system in which a secondary porosity is developed due to dolomitization and cement/grain dissolution processes.