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Przestrzenne badanie systemu porowego skał węglanowych na podstawie cyfrowej analizy obrazów mikrotomograficznych z wykorzystaniem języka Python

Fheed Adam, Hadro Piotr

Przegląd Geologiczny

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2021

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Vol. 69, nr 6

357--360

EN

The main aim of this contribution is to combine a Python-supported analysis of X-ray microtomography (µCT) images and the transmitted-light microscopy to resolve the factors controlling the variability of petrophysical parameters in carbonate rocks. A self-developed Python script for the evaluation of pore connectivity and the computation of pore sizes based on µCT data was prepared. The script was launched on a carbonate sample with drawn from a drill core representing the Late Permian Zechstein Limestone (Ca1) formation from the Wolsztyn Ridge area in West Poland. The sample was taken from the upper part of the isolated Kokorzyn Reef, corresponding to a brachiopod and bivalve-rich zone. The plug had a cylindrical shape, the diameter of 2.54 cm and the height of approximately 4.6cm. The entire volume of the plug was scanned using a GE Nanotom Sdevice. The 3D-reconstructeddatasetobtainedwith spatial resolution of 0.02 mm underwent cropping, contrast adjustment, noise reduction and porosity extraction using open-source Fiji software. The binarized porosity image was loaded into the Python script. Python scripting was found efficient in carbonate pore system examination. The code first extracted the connected pore system of the largest volume and computed the smallest distances between porosity voxels and corresponding pore walls. The obtained results were confronted with the spatially-adjusted microphotographs taken in plane-polarized transmitted light. The results have shown that narrow and isolated pores occurred within the spines of brachiopods. The largest voids were found inside the brachiopod shells. Moreover, many pores were associated with partially dissolved fragments of bivalves. Porosity reduction was -most outlined in the zones showing the scarcity of fossils.

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Wykorzystanie rentgenowskiej mikrotomografii komputerowej i cyfrowej analizy obrazu do petrologicznej charakterystyki skał węglanowych

Strzelecki Piotr Jan, Fheed Adam, Radzik Natalia, Świerczewska Anna

Przegląd Geologiczny

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2019

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Vol. 67, nr 3

195--197

EN

The paper briefly describes a possible application of X-ray computed microtomography studies followed by digital image analysis, enabling petrological assessment of carbonate rocks. The contribution presents an example of a complex, qualitative and quantitative approach aiming at deriving shape, geometry and spatial orientation of rock components as applied for a carbonate reservoir rock sample from the Zechstein Limestone (Ca1) strata. Apart from the basic properties of the analyzed objects, such as volume, surface area and number, detailed shape descriptors were obtained (compactness, sphericity, elongation, flatness, spareness). The presented approach allows for obtaining detailed 3D results at the microscopic scale, enabling extensive characterization of the studied material geometry. The methods proposed could be applied for other rock types as well.

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The impact of fossils on diagenetically controlled reservoir quality : the Zechstein Brońsko Reef

Fheed Adam

Annales Societatis Geologorum Poloniae

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2019

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Vol. 89, No. 1

47--81

EN

Although the sedimentation and diagenesis of the Polish Zechstein Limestone strata (Ca1, Permian) already have been investigated, relatively little has been done to resolve their petrophysical potential. Therefore, the gap between sedimentological and petrophysical studies was bridged through an integrated analysis of geological and geophysical data. The results of core description, polarized-light microscopy, well log interpretations and laboratory measurements on core samples were combined with previously published nuclear magnetic resonance (NMR) and X-ray microtomography (μCT) data, especially helpful in the recognition of pore geometry. The Ca1 strata of the Brońsko-1 and Brońsko-2 wells, located on the Zechstein Brońsko Reef (West Poland), were studied to determine the influence of fossils on porosity and permeability. It was concluded that greater diversification of the original biota led to an increase in porosity and variation in pore geometry. While encrusting organisms such as foraminifers promoted the development of channel and fracture porosity, the dissolution of the primarily aragonitic bivalve and gastropod shells and the shells of terebratulid brachiopods often gave rise to the formation of cavernous and mouldic porosity. The channels appear to be most common in the bryozoan-foraminifer biofacies, representing a shallowing of the depositional environment. Caverns, in turn, corresponded to the organisms of the brachiopod-bryozoan and the lightly karstified bivalve-gastropod biofacies, both of which probably experienced the influence of sabkha conditions, leading to a general decrease in porosity. The bryozoan zoecia tended to enhance both primary intraparticle voids, and after their dissolution, secondary intraparticle pores, which showed limited connectivity in the high-energy Acanthocladia biofacies, where considerable fragmentation of fossils took place, hence decreasing the permeability. Anhydrite cementation was found to be the most pronounced factor controlling porosity destruction, while dolomitization enhanced it significantly, especially for the stromatolitic biofacies, where small, unconnected vugs were formed owing to this process. The permeability is typically below 100 mD, and this is caused by the rich diagenetic history of the reef, that recorded marine, sabkha-related and burial cementation, now represented by the different fabrics of anhydrite, calcite, and dolomite.