Petrographic Image Analysis Research Articles

Experiment on visualizing micro-level surface characters of sediment sections: a methodological approach to reflectance-based alternative petrographic image analysis

This paper discusses an experiment on digital imaging and visualizing the surface condition of the sediment depositions. For that purpose, a part of South Tripura district was selected as sampling site. Physically, the selected area is located in a fold belt and preserves the history of Tertiary–Quaternary landform evolution in the main types of sediment depositions. Three samples, each from the different types of Tertiary depositions, were finally taken for thick section making, optical microscopy under reflected light, and soft computing. Geometric optical measurement and physical optical measurement were done to understand the surface condition of Bokabil, Tipam, and Duplitila samples by bidirectional reflectance distribution function and radiometric scales (within 0–255 digital number values). Maximum surface smoothness or near-perfect reflection surface was measured by brightness–contrast slicing operation.

Evaluation of the alkali–silica reactivity potential of sands

The alkali–silica reactivity potential of 20 different Quaternary natural aggregates (sands and gravels) from the Czech Republic has been evaluated by petrographic and dilatometric methods. Petrographic techniques, both qualitative (optical and scanning electron microscope (SEM)/energy dispersive spectrometer (EDS) microscopy of thin sections) and quantitative (petrographic image analysis of thin sections), have been applied for the disused specimens. The dilation of the mortar-bar test specimens (according to ASTM C1260) ranged nine samples to the non-reactive, nine samples to reactive and two samples to potentially reactive categories. These categories, based on the dilation values, do not however satisfactorily correlate to the volumes of individual groups of aggregates identified petrographically in mortar-bars. More detailed petrographic examination showed the subdivision according to the presence/absence of deformation sings inhibitors and/or grain size. These results show that the optical microscopy of mortar-bar specimens provides detailed identification of alkali reactive samples according to their spatial relationship with ASR products. The same approach also allows direct identification of gels and alkali–silica reactive fragments.

Some observations from radiometric ‘8 bit’ data of sediment thin sections based on alternative petrographic image analysis method

This paper deals with the experiment of sediment microstructure analysis especially microfabric mapping by digital imaging. For that purpose the greyscale images (Red band from RGB combination) of the thin sections have been prepared from the selected 12 samples. The basis of this mapping is the reflectance capacity of different sediments which is influenced by the physical parameters like grain size and colour. The reflectances of different sediments are represented in digital format by different DN values from 0–255 within the radiometric ranges of ‘8 bit’ data. Density slicing has been chosen as the method of microstructure mapping in this research. This study shows that lower DN values normally present dark coloured coarser sand and clay while higher DN values present light coloured finer sediment samples. In the selected samples for this study the maximum DN value has been found from micaceous materials. Another remarkable thing observed from the microfabric mapping is that the presence of coarser sediments forms complex microfabric pattern than the finer sediments in the study area. Though this method have some demerits, still its simple technique can be very useful for accurate microstructure analysis.

Methodology of analytical study for provenance determination of calcitic, calcite–dolomitic and impure marbles from historical quarries in the Czech Republic

Abstract The present provenance study was focused on marbles from historical quarries of one geological unit (Bohemian Massif, Czech Republic) exhibiting complex polyphase geological evolution. A combination of mineralogical–petrographic, geochemical and physical methods has been tested i.e. optical microscopy (OM) of the whole rock, X-ray diffraction (XRD) of the insoluble residues, petrographic image analysis (PIA) of carbonate grains, cathodoluminescence (CL) of microfacies, stable isotope ratio analysis (SIRA) of carbonates in the groundmass and secondary veins, Raman microspectrometry (RM) of the carbonaceous matter and bulk magnetic susceptibility (MS) of the whole rock. Based on the results of historical quarries and the artefacts from Pernstejn Castle and Prague Castle, the most effective way for provenance determination of marbles seems to be a combination of petrographic methods (including quantitative approaches), cathodoluminescence, and stable isotope study. Less conventional methods (e.g. Raman microspectrometry or physical properties like bulk magnetic susceptibility) are very useful for provenance studies on impure calcitic and dolomitic marbles that include carbonaceous matter, magnetic minerals or silicates. For the first time, Raman data on reduced carbonaceous matter permitted differentiation amongst marbles of different origin.

Petrographic identification of alkali–silica reactive aggregates in concrete from 20th century bridges

Cracks and white coatings have been observed in a number of concrete bridges constructed during the 20th century. The observed damage phenomena have been attributed to the alkali–silica reaction (ASR) after following detailed macroscopic examination. Several analytical approaches – optical microscopy of thin sections, petrographic image analysis and SEM/EDS study – were employed in order to: (1) quantify the extent of the damage (volume percentage of alkali–silica gel); (2) determine the causes of the damage. The presence of alkali–silica gels is controlled by the petrography of aggregates where monomineral quartz aggregates, metagreywacke, pellite and metasedimentary rock fragments contribute significantly to ASR development. Other phases (feldspars) and fragments of magmatic native rocks (granite, diorite, and volcanic rocks) have not been shown to have any influence on ASR. The volume of alkali–silica gels in the studied concrete samples (ranging from 0.1 to 0.9 vol.%) increases with increasing age of the bridge.

How depositional texture and diagenesis control petrophysical and elastic properties of samples from five North Sea chalk fields

Chalk samples from Dan, Tyra, South Arne, Valhall and Ekofisk fields were collected from hydrocarbon-bearing intervals in the Cretaceous Tor and Palaeogene Ekofisk formations in the central North Sea. The samples were compared with respect to stable isotope ratios, lithotype, texture, porosity, permeability, capillary entry pressure, as well as the dynamic elastic Biot's coefficient and Poisson's ratio. The depositional texture and present grain-size distribution were quantified by petrographic image analysis. Oxygen isotope ratio and Biot's coefficient were used as indicators of cementation. Porosity varies more than 20 porosity units within each hydrocarbon field and is controlled by three parameters: (1) sorting as expressed by Dunham texture, so that mudstones tend to have highest porosity and packstones the lowest; (2) sorting of the carbonate mud, where a mixture of clay-size chalk particles and silicates tend to reduce porosity; and (3) by pore-filling cementation. The relative significance of these parameters varies with field and formation. The presence of chalk clasts as an indicator of re-deposited chalk seems to have no relationship to porosity. Permeability and capillary entry pressure depend on porosity and mineral content as expressed in specific surface. Prediction of permeability and capillary entry pressure may be aided by information on carbonate content or on Poisson's ratio.

Assessment of rock geomechanical quality by quantitative rock fabric coefficients: Limitations and possible source of misinterpretations

Rock microfabrics were quantified by image measurement system (petrographic image analysis) of thin sections. Along with common measured parameters (grain area and size, length of major and minor axes and their orientation), some quantitative parameters (aspect ratio, grain boundary smoothness) and fabric coefficients (micropetrographic quality index ( K), “texture” coefficient (TC), indexes of interlocking ( t) and grain size homogeneity ( g)) were determined. The reliability of these parameters for the evaluation of geomechanical properties was tested on the set of granitic rocks showing pronounced variability in rock mechanical properties. None of the tested rock fabric coefficients or parameters proved a close correlation to rock mechanical properties except grain size. Based on experimental findings, the grain size is, along with porosity, the controlling factor of rock mechanical properties of genetically and mineralogically similar rocks. Obliteration of the real effects of rock fabric parameters on the mechanical properties of rocks by application of complex fabric coefficients disables their practical use in petrography applied to geomechanics.

Porosity–permeability relationships in Miocene carbonate platforms and slopes seaward of the Great Barrier Reef, Australia (ODP Leg 194, Marion Plateau)

AbstractThis paper reports a series of 700 porosity–permeability analyses and supporting petrographic and sedimentologic descriptions from Early to Late Miocene carbonate strata cored on the Marion Plateau, offshore from north‐eastern Australia, during Ocean Drilling Program (ODP) Leg 194. The samples analysed are not only mainly coarse bioclastic limestones and dolomitized equivalents from platform‐top facies, but also include 79 plugs from deeper‐water slope to hemipelagic drift facies. Outstanding characteristics of this data set are the wide ranges of porosity and permeability in both limestones and dolostones, the large degree of short‐range heterogeneity typical of these strata, and the better porosity–permeability correlation of dolostones than limestones. The platforms have experienced widely varying calcite cementation, dolomitization and dissolution but show little clear evidence of meteoric diagenesis, suggesting that subaerial exposure may have played little role in porosity–permeability evolution. Permeability‐for‐given‐porosity is controlled by grain size and calcite cement content in grainstones and by occurrence of larger shelter pores and vugs in mud‐rich samples. Dolomitization tends to reduce the variation of permeability‐for‐given‐porosity by recrystallizing mud matrix to form intercrystalline macroporosity that connects vugs and moulds to become integrated with the effective pore system. As a result, there are no differences in permeability–porosity trends for different dolostone textures, whether dominated by intercrystalline, vuggy, or preserved intergranular pore types. Two platform‐top sites separated by only 5 km display a major lateral variation in dolostone porosity–permeability characteristics within the youngest dolostone units. This difference is interpreted as reflecting a relatively ‘windward’ (current‐facing) setting of the site with the overall higher permeability‐for‐given‐porosity (Site 1199) that led to less muddy depositional facies, greater cementation, and lesser grain dissolution. Pore‐geometry parameters measured by petrographic image analysis confirm that the ‘windward’ dolostones have pores that are both larger and less intricate than dolostones comprising the more current‐protected location.

Determining the petrographic fabric of a compacted soil using semivariance analysis: sample preparation and digital petrographic image analysis

Samples from compacted soil have been prepared for scanning electron microscopy (SEM) using a technique that has been developed in order preserve the property under investigation. Using the SEM images, digital image analysis has been used to estimate semivariograms for the pore space of a compacted artificial soil. Strain ellipses quantifying the degree of heterogeneity have been constructed using the structural information provided by the semivariograms. The results show that the physical response of the pore space depends on pore size. In the case of the artificial soil, investigated here, two structural regimes were found to exist at two different scales.

Pore microgeometry analysis in low-resistivity sandstone reservoirs

The objective of this work is to analyse the pore microgeometry and its effect on petrophysical properties in six low-resistivity sandstone reservoirs by combining a 2D quantitative petrographic image analysis (PIA) and 3D petrophysical tools. The classic petrophysical tools enable the measurement of different classic reservoir properties such as specific surface area, average pore diameter, pore size distribution, macroporosity and microporosity, capillary pressure versus saturation, pore chamber–pore throat diameter ratio, electrical properties and permeability. The petrographic image analysis quantifies pore microgeometry in more than four orders of magnitude, from submicron to millimeter scale. Chloritic low-resistivity sandstones show dual porosity structure defined as chloritic texture. The pore microgeometrical parameters measured by petrographic image analysis allow one to model different reservoir properties such as capillary pressure, permeability and electrical behaviour. The results obtained in these models show that pore microgeometry plays an important role in the physical properties of low-resistivity sandstone reservoirs.

Some microstructural aspects of strength variation in rocks

The experimental study of rock strength revealed a remarkable mechanical variation in closely related rocks. This variation is explained through a quantitative analysis of microstructures. The oriented dry rock specimens were loaded at a constant stress rate and the uniaxial compressive strength with deformation, was recorded together. Microstructures were analysed in thin sections using petrographic image analysis, making it possible to determine size, shape and the shape-preferred orientation of individual grains, grain size distribution and modal composition. The typical grain size has been found to be the main microstructural factor controlling strength variation in groups of rocks which are closely related mineralogically. The increase of strength anisotropy is connected with an increasing degree of shape-preferred orientation of rock-forming minerals.

Petrophysical properties of porous medium from Petrographic Image Analysis data

Petrographic Image Analysis (PIA) is a well-established rapid two-dimensional (2D) method to quantify pore and solid space in reservoirs and different porous materials. This paper aims to describe a method of characterization and quantification of petrophysical properties in carbonate pore systems using Petrographic Image Analysis over more than three orders of magnitude, from a submicron to a millimeter scale. We integrated two kinds of multiscaled digital image: the transmitted-light-colored petrographic images which allowed us to characterize the macroporosity; the Back-Scattered Electrons (BSE) grey level images which gave us information about microporosity. This technique enabled us to measure different classical petrophysical properties such as pore area, specific surface area, average pore diameter, distribution of pore size, pore shape factor, macroporosity and microporosity. We used image parameters in order to obtain the model of capillary pressure curve versus saturation ( P c– S). On the other hand, using empirical equations of permeability derived from Carman–Kozeny expression and a bundle of capillary tubes model, we were able to calculate the permeability of carbonate pore systems from different image parameters. The same petrophysical parameters were directly measured on core through classical three-dimensional petrophysical techniques (3D), such as Hg-injection porosimetry, permeametry and the BET technique. Finally, we compared the values different petrophysical properties of carbonate pore systems, obtained from 2D image analysis (PIA) and 3D classical petrophysical techniques.

ABSTRACT: Pore Measurements by Petrographic Image Analysis: Implications for Rapid Identification and Ranking of Reservoir Flow Units, Happy Spraberry Field, Garza County, Texas

ABSTRACT: Pore Measurements by Petrographic Image Analysis: Implications for Rapid Identification and Ranking of Reservoir Flow Units, Happy Spraberry Field, Garza County, Texas

Probing the pore space of geothermal reservoir sandstones by Nuclear Magnetic Resonance

Pulsed-Field-Gradient–Nuclear Magnetic Resonance (PFG–NMR) is an interesting method to determine microscopic but volumetrically averaged properties of pore space. In the present paper a number of sandstone samples, taken from drill cores of geothermal wells in North Germany, have been investigated. The time-dependent self-diffusion of water molecules in their confined geometry is used to probe the pore space. The short-time behaviour of the self-diffusion coefficient (anomalous diffusion) in the porous matrix allows the determination of the surface-to-pore volume ratio S/V p. At long diffusion times, molecules scout the tortuosity of the interconnected pore space of the sandstones. The NMR results were compared with data from petrographic image analysis (PIA), adsorption experiments and electric conductivity measurements. The PFG–NMR measurements give surface-to-pore volume ratios S/V p that are comparable to those estimated with the petrographic image analysis. The tortuosities match in most cases data from conductivity measurements, so the PFG–NMR is regarded as an appropriate tool to determine this quantity. The results are not influenced by the adherence of ‘scout-molecules’ to the pore walls. The surface-to-pore volume ratios and tortuosities were used to calculate permeabilities of the systems of interest, which were in good agreement with measured core-plug permeabilities. Results of additional NMR relaxation experiments are used to obtain adsorption isotherms for cations at active surface sites.

ABSTRACT: Pore Measurements by Petrographic Image Analysis: Implications for Rapid Identification and Ranking of Reservoir Flow Units, Happy Spraberry Field, Garza County, Texas

ABSTRACT: Pore Measurements by Petrographic Image Analysis: Implications for Rapid Identification and Ranking of Reservoir Flow Units, Happy Spraberry Field, Garza County, Texas

Abstract: Spatial Analysis of Fabric Elements in the Berea Sandstone through Petrographic Image Analysis

Abstract: Spatial Analysis of Fabric Elements in the Berea Sandstone through Petrographic Image Analysis

Abstract: Correlation of Porosity Types Derived From NMR Data and Petrographic Image Analysis

Abstract: Correlation of Porosity Types Derived From NMR Data and Petrographic Image Analysis

Abstract: Application of a Novel High Resolution Object Recognition Algorithm for Petrographic Image Analysis of Reservoir Facies from the Rabbit Hills Oil Field, Montana

Abstract: Application of a Novel High Resolution Object Recognition Algorithm for Petrographic Image Analysis of Reservoir Facies from the Rabbit Hills Oil Field, Montana

Abstract: Application of Probe Permeametry, CT-scanning and Petrographic Image Analysis to the Understanding of Petrophysical and Pore Geometry Properties: Carmopolis Conglomerate Reservoirs, Sergipe-Alagoas Basin, Northeastern Brazil 

Abstract: Application of Probe Permeametry, CT-scanning and Petrographic Image Analysis to the Understanding of Petrophysical and Pore Geometry Properties: Carmopolis Conglomerate Reservoirs, Sergipe-Alagoas Basin, Northeastern Brazil 

Causes of permeability variation in a Lower Cretaceous reservoir unit in the West Siberian Basin, Russia

Samples of the Lower Cretaceous BS 10 reservoir, taken from 11 oil fields in the central part of the West Siberian Basin, show a permeability variation of more than 4 orders of magnitude at the scale of the core plug. Much of this variation occurs in samples that fall within the fine-grained Wentworth class. However, application of 2-D Fourier analysis and other methods of petrographic image analysis demonstrates the existence of a real, but subtle, variation in grain size that provides an important control on permeability. Reservoir quality will be best in the facies that represent the highest depositional energy.