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X-RAY MICROTOMOGRAPHY-BASED PORE STRUCTURE ANALYSIS OF THE PERMIAN REEF ROCKS (WEST POLAND)

Adam Fheed, Piotr Strzelecki

Abstract

Biogenic origin of the carbonate reef build-ups poses multiple questions associated with spatial porosity distribution in corresponding hydrocarbon reservoirs. Consequently, this paper focuses on 3D characterization of the voids observed within chosen carbonate samples. Not only the pore type and geometry are interpreted, but also the origin of pores is attempted to be resolved. Zechstein (Permian) biogenic reef carbonates were examined. The rocks have been withdrawn from the central part of the isolated Wielichowo Reef located in West Poland. The Reef is known to bear gas resources. Chosen carbonates were studied under the polarized-microscope. Two corresponding plug samples were subjected to the microtomographic (?CT) imaging with a resolution of 0.02 mm. The obtained images were processed in the ImageJ software using the 3D object counter plugin. According to the obtained results, the two studied samples show significant geometric and genetic differences. Two limestone types were distinguished: (1) the meteorically-dissolved rudstone of Fenestella biofacies with cavernous and intraparticle porosity, and (2) the packstone bearing large voids related to Acanthocladia bryozoans. In both cases, at least one population of highly-communicated macropores could have been observed. The macropores are always related to the former shells and skeletons of brachiopods and bryozoans. High connectivity of the voids is manifested by an occurrence of several pores comprising the majority of the total porosity in both samples. Lower surface to volume ratios in the case of the studied rudstone suggest that the pores have higher specific surface area in comparison to the examined packstone. Moreover, local trends in spatial distribution of the voids can be observed in the tested samples. It can thus be concluded that both environmental conditions and further diagenetic processes such as пїЅ for instance пїЅ dissolution, have a significant impact on the final rock texture. The ?CT-based spatial image analysis seems to be an adequate tool for performing a comprehensive study of carbonate pore structure.

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DOI resolver: doi.org/10.5593/sgem2017h/15/s06.083

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