Internal structure and origin of modern salt crust of Salar de Uyuni (Bolivia) salt pan based on tomographic research

This paper presents the results of a study on the internal structure of modern salt crust of Salar de Uyuni in SW Bolivia. Additionally, the structure of desiccation fissure infill was investigated. X-ray microtomography was used as the main analytical method because it enabled the complete structure of the sample's interior to be imaged without its destruction. Based on microtomographic images three layers were distinguished in the crust between the surface and its base: a halite shell at the top, a cellular halite layer in the middle and a large-pore halite layer at the base. Results revealed that the desiccation fissures are filled with extremely porous bubble-halite. Distribution of mud in the sample as well as wash-out of the surfical halite crystals indicate the cyclicity of halite dissolution, its crystallisation and mud accumulation. These observations provide an explanation for low rate salt accumulation in the salt pan. This leads to the conclusion that the observed layering in the rocks does not reflect annual sedimentation-evaporation cycles but rather long-term cycles

Determination of reservoir properties through the use of computed X-ray microtomography – eolian sandstone examples

A possibility of examination of the rock pore structure by means of the X-ray computed microtomography was presented. Parameters characterizing the pore structure, i.e. porosity and coefficient of homogeneity of pore structure by local porosity examination and box counting dimension and mean chord length and normalized Euler number and coordination number were determined through pore structure image analyses. Complementary methods as pycnometry, mercury injection porosimetry and NMR were used to determine porosity and other factors to make the comparison and determine mutual relationships between petrophysical properties obtained from various sources.The study covered Rotliegend sandstones of eolian origin. Reservoir properties laboratory investigations were focused in three areas located in the marginal part of the eastern erg and middle part of the Polish Lowland Permian Basin. Rotliegend sediments in the study showed changeability in petrography and reservoir properties so the data were grouped into three parts according to geological regions. Computed X-ray microtomography gave differentiation of the investigated areas with respect to their pore structure and porosity development. This differentiation was confirmed by means of other applied laboratory methods

Modeling non-Darcy flows in realistic pore-scale proppant geometries

The ability to evaluate the effective permeability of proppant packs is useful in predicting the efficiency of hydraulic fracture installations. In this paper we propose a computational approach combining microimaging data from X-ray computed microtomography, the simulations of flow at pore-scale, and an upscaling process which identifies the effective model parameters at the core-scale. With this computational approach applied to proppant pack we confirm the reduction in the fracture conductivity and subsequent reduction in the productivity of a hydraulically fractured reservoir due to the high flow rates and to the migration of fine particles resulting in pore throat bridging

Research results of triaxial geomechanical tests of a coal sample in the light of tomographic tests

The study aimed to check the possibility of using computed tomography to observe fractures in coal samples before and after a triaxial compression test (TRX). The paper presents an innovative use of two specialized laboratory techniques: computed tomography and geomechanical triaxial compression test. Geomechanical tests were performed on a TRX-070, GCTS (USA) measuring triaxial system. A full stress-strain characteristic was recorded. Also, during the triaxial compression tests, the P and S wave velocities were measured and dynamic elastic moduli were determined. The results were compared. The sample was analyzed in two stages: CT measurement performed on raw coal sample (stage 1) and after the TRX test which destroyed the sample structure (stage 2). First, the sample was scanned reflecting the initial pores and microcracks system. The final stage represents the sample after the geomechanical test. A detailed pore structure analysis was performed for each of the stages. As a result of the proposed above-mentioned method, images of the pore structure were obtained after each step. The sample was analyzed for crack propagation and changes in the pore structure. The qualitative and quantitative interpretation was based on the determination of the number of voids, crack diameters, collapse angles, and comparison of the pore structure between the initial state of the sample and after the triaxial test. In the first stage (before the test), the largest object (identified as a microcrack) had a volume of approximately 16 mm3, after the sample was stress-tested (after the sample was destroyed), the largest identified object was about 15 times larger (240 mm3). It appeared that the coal sample was prone to fracturing in defined directions. Comprehensive research has demonstrated the legitimacy of using the proposed methodology to evaluate changes in the sample structure during the triaxial test

Pomiary porowatości skał metodą rentgenowskiej mikrotomografii komputerowej (Micro-CT) Rock porosity measurements using Roentgen computed microtomography (Micro-CT) /

Tyt. z nagłówka.Bibliografia s. 623-624.Dostępny również w formie drukowanej.ABSTRACT: Roentgen computed microtomography is an imaging technique that generates high resolution 3D images of internal structure, basing on difference in X-rays absorption inside the sample. Micro-CT provides new possibilities to obtain up to few microns resolution images of reservoir rocks in non destructive way. Such images enables to visualize and quantitative analysis of mineral composition and pore structure (volume, shape and pore throat diameter), which can be used to better understanding petrophysical properties such as permeability. This paper shows test of direct, quantitative porosity measurement based on 3D images obtained using Benchtop device and AVIZO software. KEYWORDS: porosity, microtomography. SŁOWA KLUCZOWE: porowatość, mikrotomografia

Determination of reservoir properties through the use of computed X-ray microtomography – eolian sandstone examples

Tyt. z nagłówka.Bibliogr. s. 246-248.The possibility of examining rock pore structure by the means of computed X-ray microtomography was presented. Parameters characterizing the pore structure, such as: porosity and coefficient of homogeneity of pore structure by local porosity examination, box counting dimension, mean chord length, normalized Euler number, as well as coordination number were all determined through pore structure image analyses. Complementary methods, such as helium pycnometry, mercury injection capillary pressure and NMR were used to determine the porosity along with other factors to make the comparison and determine mutual relationships between petrophysical properties obtained from various sources. The study covered the Rotliegend sandstones of eolian origin. Laboratory investigation of the reservoir properties was focused on three areas, according to their geological regions, where the Rotliegend sediments showed changeability in geological features and reservoir properties. Computed X-ray microtomography showed differentiation between the investigated areas, with respect to their pore structure and porosity development. This differentiation was confirmed by means of other applied laboratory methods.Dostępny również w formie drukowanej.KEYWORDS: computed X-ray microtomography reservoir rocks, petrophysical properties, Rotliegend sandstones

Zwiększanie możliwości wyznaczania parametrów zbiornikowych skał z wykorzystaniem rentgenowskiej mikrotomografii komputerowej

Promotor: Jadwiga Jarzyna.Niepublikowana praca doktorska.Tyt. z ekranu tyt.Praca doktorska. Akademia Górniczo-Hutnicza im. Stanisława Staszica (Kraków), 2013.Zawiera bibliogr.Dostępna również w wersji drukowanej.Tryb dostępu: Internet.Opis rentgenowskiej mikrotomografii komputerowej, podstawy mikrotomografii rentgenowskiej, podstawowe własności promieniowania rentgenowskiego, oddziaływanie promieniowania rentgenowskiego z materią, budowa rentgenowskiego mikrotomografu komputerowego, otrzymywanie danych za pomocą mikrotomografu, przebieg pomiaru, rekonstrukcja obrazów, sztuczne elementy (artefakty) rekonstrukcji, analiza przestrzennych obrazów struktury porów, przetwarzanie obrazu, analiza liczbowa struktury porowej, wybór reprezentatywnego fragmentu próbki, opis obszaru badań, obszar badań, charakterystyka obszaru badań, zespoły facjalne górnego czerwonego spągowca, charakterystyka petrograficzna piaskowców eolicznych, wyniki wstępnych badań laboratoryjnych, analiza uzyskanych wyników, analiza niepewności wyników pomiarów, zestawienie zależności w celu oceny możliwości określania predykcji parametró

Calibration of dual energy CT scans for rock core examination

: Jedno z pierwszych zastosowań rentgenowskiej tomografii komputerowej w geologii miało miejsce w 1974 roku. Tomografia rentgenowska (CT) umożliwia nieinwazyjne obrazowanie badanych przedmiotów. Wynikiem pomiaru tomograficznego jest przestrzenny obraz, przedstawiający zmiany absorpcji promieniowania rentgenowskiego. Powstaje on poprzez wyliczenie, podczas procesu rekonstrukcji, wartości absorpcji dla każdego punktu badanego przedmiotu. Istotną zaletą tomografów komputerowych jest możliwość przebadania dużych obiektów (metrowych odcinków rdzenia) w bardzo krótkim czasie. Ich wadą jest natomiast względnie niska rozdzielczość pomiaru. Każdy woksel na obrazie tomograficznym ma przypisaną konkretną wartość zaczernienia proporcjonalną do liniowego współczynnika tłumienia, zależną od gęstości elektronowej i efektywnej liczby atomowej, uśrednionych w obrazowanej przestrzeni (zakres uśredniania określa rozdzielczość obrazu tomograficznego). Dysponując dwoma obrazami, zarejestrowanymi przy dwóch różnych energiach pomiaru, można podjąć próbę rozdziału obrazu na dwie składowe: pierwszą – zależną od gęstości elektronowej i drugą – zależną od efektywnej liczby atomowej. Celem opisanych prac jest pokazanie możliwości wykorzystania dwuenergetycznej tomografii komputerowej (DECT) do charakterystyki litologiczno-gęstościowej rdzeni wiertniczych. Aby wykorzystać obrazy tomograficzne do otrzymania wymienionych wielkości fizykochemicznych konieczna jest standaryzacja obrazów. W pracy przedstawiono proces wyznaczania współczynników kalibracyjnych, które są niezbędne do przeliczania wartości współczynników absorpcji, będących bezpośrednim wynikiem rekonstrukcji pomiaru tomograficznego na wartości gęstości elektronowej oraz efektywnej liczby atomowej Z. W artykule zaprezentowano proces kalibracji z wykorzystaniem wzorcowych minerałów. Wyliczone z analizy obrazów wartości próbek wzorcowych, porównano z wartościami wyznaczonymi metodami laboratoryjnymi. Przykład zastosowania wyników przedstawiono na przebadanym fragmencie obrazu rdzenia piaskowca, zawierającego szczelinę wypełniona kalcytem.One of the first applications of X-ray computed tomography in geology took place in 1974. X-ray tomography (CT) allows non-invasive imaging of the examined objects. The result of a tomographic measurement is a spatial image, showing the changes in X-ray absorption value for each point of the examined object, which are a result of calculations during the reconstruction process. An important advantage of computer tomographs is the ability to test large objects (meter sections of the core) in a very short time, while the disadvantage is the relatively low resolution of the measurement. Each voxel in the tomographic image has a specific grey value, proportional to the linear attenuation coefficient, depending on the electron density and the effective atomic number averaged in the imaged space (the averaging range is determined by the resolution of the tomographic image). Two tomographic images registered at two different energies, allows the deconvolution of the images into two components: the first – dependent on the electron density and the second – dependent on the effective atomic number. The aim of this study is to show the possibility of using dual energy computed tomography (DECT) to litho-density characterization of rock cores. In order to use tomographic images to obtain the above-mentioned physicochemical values, it is necessary to standardize CT images. The paper presents the process of determining calibration coefficients, which are necessary to convert the values of absorption coefficients, which are a direct result of CT reconstruction, into density values and effective Z atomic number. The article presents the calibration process with the use of reference rock fragments. The values of the standard samples computed from the analysis of images were compared with the values determined by laboratory methods. An example of the application of results is presented on the examined part of the image of the sandstone core, containing a calcite-filled fracture

Characteristics of Rotliegend sediments in view of X-ray microtomohraphy and optical microscopy investigations

The article presents the results of microtomographic and petrographic investigations of Rotliegend sandstones collected from core material from wells located in the area of the Fore-Sudetic Monocline in its central and northern parts and also on the border of the Fore-Sudetic Monocline and the Mogilno - Łódź Synclinorium. Three areas were selected for the study: Czarna Wieś–Parzęczewo (19 samples), Środa Wielkopolska–Kromolice (21 samples) and Siekierki–Miłosław (21 samples). The aim of the petrologic and microtomographic studies was to investigate how the different reservoir properties of sandstones will be reflected in the results of the methods used. Strong differences between samples from the region of Środa Wielkopolska–Kromolice and the other studied areas have been demonstrated. In the case of this area several key factors were noticed: the highest average value of effective porosity; the highest average content of pores belonging to class VII (pore volume subsystem classification); three times higher average value of the CT porosity coefficient and the largest length of the average chord. Also in terms of petrography (composition of grains, cement type) it is a region where major differences, especially compared to the region of Czarna Wieś–Parzęczewo, can be seen. Based on the obtained results, it was possible to rank the examined regions in terms of their reservoir properties – from the worst (Czarna Wieś–Parzęczewo) to the best (Środa Wielkopolska–Kromolice). These conclusions are also confirmed by other petrophysical analyses (eg. mercury porosimetry, permeability analysis). Combination of the obtained microtomographic and petrographic results allowed to obtain a full characterization of the investigated samples – both in terms of the mineralogical composition of grains, as well as the development of the pore space. These data, especially in combination with the results of density and porosity analyses (helium pycnometry and mercury porosimetry), open up a number of possibilities to carry out different types of modeling (porosity, permeability) both on the scale of the sample itself, as well as the scale of a single well or even the whole basin, which is crucial for creating a hydrocarbon exploration strategy

The study of application of geometric parameters of the pore space from tomographic images in the context of NMR measurements, mercury porosimetry and helium porosimetry

Głównym celem pracy była ocena przydatności wyników interpretacji ilościowej, uzyskanej z obrazowania wewnętrznej struktury próbek skał z wykorzystaniem metody tomografii komputerowej, do szacowania parametrów zbiornikowych takich jak porowatość czy przepuszczalność. W pracy badano zależności korelacyjne pomiędzy parametrami przestrzeni porowej uzyskanymi z analizy obrazów tomografii komputerowej a wynikami standardowych badań laboratoryjnych. Materiał badawczy składał się z próbek piaskowców czerwonego spągowca, facji eolicznej, pobranych z obszaru Niżu Polskiego. Do analiz wybrano kilkadziesiąt próbek skał piaskowców czerwonego spągowca, dla których policzono 69 parametrów. Interpretacja jakościowa i ilościowa polegała na porównaniu parametrów otrzymanych z analizy obrazu tomograficznego z wcześniej uzyskanymi wynikami analiz laboratoryjnych obejmujących następujące metody badawcze: porozymetrię helową (Por.He), spektrometrię jądrowego rezonansu magnetycznego (NMR), porozymetrię rtęciową (Por.Hg) i przepuszczalność absolutną (przepuszcz). Utworzono macierze korelacji dla wszystkich dostępnych parametrów, do pracy wybrano korelacje istotne, o najwyższym współczynniku korelacji liniowej. Zaobserwowano istotne zależności liniowe pomiędzy parametrami wyznaczonymi z analizy obrazów CT i innych metod badawczych. Uzyskano modele pozwalające na szacowanie przepuszczalności, porowatości i zawartości wody nieredukowalnej na podstawie parametrów geometrycznych otrzymanych z obrazów tomograficznych (współczynnik kształtu, charakterystyka Eulera czy powierzchnia właściwa). W efekcie możliwe jest wstępne oszacowanie parametrów petrofizycznych jedynie na bazie wyników z nieniszczącej metody CT. W przypadku obrazowania tomograficznego pełnych rdzeni uzyskane związki pozwalają na wstępną estymację rozkładu porowatości i gęstości objętościowej w całym rdzeniu, co może być pomocne podczas typowania miejsc do poboru próbek rdzeni przeznaczonych do szczegółowych badań laboratoryjnych.The main purpose of the study was to assess the usefulness of the results of quantitative interpretation of computed tomography (CT) images of rocks’ pore structure for the estimation of reservoir parameters, such as porosity and permeability. This study presents results of correlation analyses between the pore space parameters obtained from the analysis of computed tomography images and the results of standard laboratory tests. The research material consisted of samples representing Rotliegend sandstones of aeolian facies, collected from core material from wells located in the Fore-Sudetic Monocline. Several dozen samples were selected for analysis, for which 69 parameters were calculated. The qualitative and quantitative interpretation consisted in comparing the parameters obtained from the analysis of the tomographic images with the previously obtained results of laboratory analyzes including the following research methods: helium porosimetry (Por.He), nuclear magnetic resonance spectrometry (NMR), mercury porosimetry (Por.Hg) and absolute permeability (let it pass). Correlation matrices for all available parameters were determined, significant correlations with the highest coefficient of linear correlation were selected as a subject of this work. Significant linear relationships were observed between the parameters determined from the analysis of CT images and other research methods. Models that were obtained allowed to estimate the permeability, porosity, and irreducible water content based on geometrical parameters obtained from tomographic images (shape factor, Euler characteristic or specific surface area). The important result of this work is the possibility to estimate petrophysical parameters based on the results of the non-destructive CT method only. In the case of tomographic imaging of whole cores, the obtained results allow for a preliminary estimation of the porosity and volume density distribution in the entire core, which may be helpful in selecting representative samples of core for detailed laboratory tests