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PETROPHYSICAL CHARACTERIZATION OF THE PORE SPACE IN GASBEARING MIOCENE ROCKS FROM THE SIEDLECZKA AREA (THE CARPATHIAN FOREDEEP, POLAND)

Dr. Grzegorz Machowski, Alicja Pstrucha, Artur KrzyЕјak

Abstract

Pore space characterization is an essential element of reservoir characterization, often based on combination of different laboratory techniques. The study concerns mercury injection capillary pressure, low field nuclear magnetic resonance, gas permeability measurements and X-ray diffraction analysis on Miocene sandstones and mudstones. Core samples were taken from several boreholes from the Siedleczka area, which is located in an important gas province of Poland пїЅ the Miocene Carpathian Foredeep Basin (southeastern Poland). In the studied area, fields produce biogenic gas from almost impermeable mudstone intervals of thickness exceeding 100 meters, which are interbedded with scarce and thin sandstone layers. Results of the applied laboratory methods allowed detailed analysis of the pore space and estimation of the crucial petrophysical parameters пїЅ porosity, permeability and water saturation. The analyzed sandstone samples reveal the porous type of the reservoir space, characterized by the high proportion of meso- (0,5 пїЅ 2,5 ?m) and macropores (> 2,5 ?m), high values of effective porosity (16 пїЅ 22%), low values of the irreducible water saturation index (below 0,1), and moderate values of permeability (several mD). The pore space of mudstone samples is dominated by nanopores (< 0,1 ?m), which results in moderate values of effective porosity (12 пїЅ 14%), high values of the irreducible water saturation index (0,3 пїЅ 0,4), and very low values of permeability (typically below 0,1 mD). The presented results suggest that the analyzed Miocene mudstones and sandstones may represent a hybrid type of reservoir rocks, with features typical of both conventional and unconventional reservoir deposits.

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