Thin-section Electron Microscopy Research Articles

Pore characteristics of black shale in Da’anzhai member of Jurassic in central Sichuan Basin, China

The lacustrine shale in the Da’anzhai member of Jurassic in the central Sichuan Basin is a key exploration target for shale oil and gas resources in China in the future. This paper presents a detailed study of shale rock types and component characteristics, shale pore types and structural characteristics, and shale pore evolution characteristics under thermal simulation conditions through experimental analyses such as rock thin section and field emission scanning electron microscopy (FE-SEM) observation, conventional physical property test, X-ray diffraction (XRD) analysis, TOC test, liquid nitrogen adsorption (LNA) test, and thermal simulation (pore) experiment. The results show that minerals in the Da’anzhai shale are mainly clay minerals, quartz, and calcite, with a small amount of feldspar, dolomite, and pyrite. In the shale oil reservoirs, there are dominantly inorganic pores (e.g. clay intergranular pores), and relatively few organic pores. The specific surface area ranges from 1.064 m2/g to 9.227 m2/g, with an average of 4.949 m2/g. The pore volume is 0.003–0.016 cm3/g, with an average of 0.010 cm3/g. Mesopores contribute the most to the total pore volume and total specific surface area. With the increase of thermal simulation temperature, the degree of shale thermal evolution increases, and the shale porosity increases, predominantly, owing to the contribution of organic pores. It is concluded that inorganic pores, especially clay intergranular pores, are the dominant pore type in the Da’anzhai shale oil reservoirs, and the evolution degree, burial time and depth of organic matter can obviously improve the organic pores.

Additions to Alpha-Sheet Based Hypotheses for the Cause of Alzheimer's Disease.

Protein amyloid-β (Aβ) oligomers with β-sheet-like backbone (β-structured) form extracellular amyloid plaques associated with Alzheimer's disease (AD). However, the relationship to AD is not known. Some investigations suggest that the toxic Aβ component has α-sheet-like backbone (α-structured) subsequently detoxified by intracellular α-to-β conversion before plaque formation. Our objective is to compare this latter hypothesis with observations made by electron microscopy of thin sections of AD-cerebral cortex. We observe irregular, 200-2,000 nm, intracellular, lipofuscin-like inclusions. Some are light-staining and smooth. Others are dark-staining and made granular by fibers that are usually overlapping and are sometimes individually seen. Aspects unusual for lipofuscin include 1) dark and light inclusions interlocking as though previously one inclusion, 2) dark inclusion-contained 2.6 nm thick sub-fibers that are bent as though α-structured, and 3) presence of inclusions in lysosomes and apparent transfer of dark inclusion material to damaged, nearby lysosomal membranes. These data suggest the following additions to α-structure-based hypotheses: 1) Lipofuscin-associated, α-structured protein toxicity to lysosomal membranes is in the chain of AD causation; 2) α-to-β detoxification of α-structured protein occurs in lipofuscin and causes dark-to-light transition that, when incomplete, is the origin of cell-to-cell transmission essential for development of AD.

Effects of confining pressure and microscale heterogeneity on hydrocarbon retention and pore evolution from artificial maturation of Eagle Ford Shale

Although shale heterogeneity has recently emerged as a key topic in unconventional petroleum systems, hydrocarbon (HC) retention and pore evolution in organic-rich shales still remain poorly constrained. In this study, an organic-rich Eagle Ford Shale sample (EqVRo = 0.92%) from a shale-oil prospecting well in South Texas was selected for gold-tube pyrolysis experiments to investigate organic matter (OM) -hosted pore development versus confining pressure during thermal maturation. Before heating, the OM-type heterogeneity and associated pore characteristics in the sample were examined by thin section and scanning electron microscopy imaging, combined with elemental mapping by X-ray energy-dispersive spectroscopy. Four forms of OM occurrence that are closely associated with different mineral matrix domains are distinguished, including the ductile oil-bearing primary OM and rigid primary OM in the siliceous-argillaceous seams, as well as the secondary OM in coccolith-rich lenses and in foraminifera chambers. From heating experiments, the pressure effect on pore evolution was found to be pronounced for the secondary OM in the foraminifera chambers, in which the coalescence of small pores to larger pores upon OM maturation was accelerated by increasing fluid pressure, accompanied by arrangement and densification of OM structures. However, the expulsion effect as a function of confining pressure seems to be evident only for the secondary OM in the coccolith-rich lenses. In contrast, the two types of primary OM in the siliceous-argillaceous seams do not show any apparent changes in pore development over the investigated pressure range of 10 to 120 MPa, probably due to stiffer mechanical properties of primary OM as compared to secondary OM. The discrepancies in pore evolution of different OM types as a response to the variation in confining pressure upon maturation primarily depend on the physical-chemical properties of these various OM materials.Of further importance, observed differences in OM evolution and associated pore characteristics in response to the variation in confining pressure imply that the microscale heterogeneity of shale fabric controls the extent of oil retention and pore evolution. In contrast to the intragranular pores in the foraminifera chambers, the intergranular pores in the coccolith-rich lenses from the Eagle Ford Shale sample are relatively smaller, yet more likely interconnected. Thus, these coccolith-associated pores may provide not only significant storage space but also a major flow pathway for HC production. Our investigation at the microscopic scale provides concepts indicating that HC retention and OM-hosted pore evolution occur differently in two contrasting types of mineral matrix pores, which is critical to successful unconventional shale oil and gas exploration in sedimentary basins.

Storage space development and hydrocarbon occurrence model controlled by lithofacies in the Eocene Jiyang Sub-basin, East China: Significance for shale oil reservoir formation

Complex mineral composition, multiple depositional processes, and strong reservoir heterogeneity cause the complexity and uniqueness of a lacustrine shale oil reservoir. Understanding the storage space development and hydrocarbon occurrence model should facilitate the analysis of the shale oil reservoir and hydrocarbon accumulation in lacustrine shales. In this study, the storage space development model for different lithofacies and the modes of hydrocarbon occurrence in different storage space were analyzed in the Es4s–Es3x shale in the Jiyang Sub-basin, East China, based on thin-section and field emission scanning electron microscopy (FE-SEM) observations, X-ray diffraction (XRD) analysis, physical property testing, and geochemical analysis. Inorganic pores, particularly recrystallization intercrystalline pores in calcite, are the key matrix pores for lacustrine shale oil. However, the types and abundance of storage space are noticeably different in various lithofacies. The hydrocarbon occurrence is mainly manifested in three states: (A) free state in interlaminar fractures, structural fractures, and abnormal pressure fractures; (B) adsorbed state in organic pores, intercrystalline pores in pyrite, and floccule pores; and (C) free state in large pore spaces, including dissolution pores and recrystallization intercrystalline pores, which can form a continuous hydrocarbon accumulation. The hydrocarbon generation potential and thermal maturity are closely associated with the lithofacies and mineral composition. The matching mechanisms of pore formation as well as hydrocarbon generation, migration, and accumulation are favorable. Among the various lithofacies, the organic-rich calcareous shale has abundant storage space, high porosity, total organic carbon content, and hydrocarbon potential, making it a “sweet spot” for shale oil exploration.

Ultrastructural examination of lung \u201ccryobiopsies\u201d from a series of fatal COVID-19 cases hardly revealed infected cells

Ultrastructural analysis of autopsy samples from COVID-19 patients usually suffers from significant structural impairment possibly caused by the rather long latency between death of the patient and an appropriate sample fixation. To improve structural preservation of the tissue, we obtained samples from ventilated patients using a trans-bronchial “cryobiopsy” within 30 min after their death and fixed them immediately for electron microscopy. Samples of six COVID-19 patients with a documented histopathology were systematically investigated by thin section electron microscopy. The different samples and areas inspected revealed the ultrastructural correlates of the different phases of diffuse alveolar damage, including detachment of the alveolar epithelium, hyperplasia of type 2 cells, exudates, and accumulation of extracellular material, such as the hyaline membranes and fibrin. Macrophages and neutrophilic granulocytes were regularly detected. Structural integrity of endothelium was intact in regions where the alveolar epithelium was already detached. Aggregates of erythrocytes, leukocytes with fibrin, and thrombocytes were not observed. Coronavirus particles were only found in and around very few cells in one of the six patient samples. The type and origin of these cells could not be assessed although the overall structural preservation of the samples allowed the identification of pulmonary cell types. Hence, the observed alveolar damage is not associated with virus presence or structural impairment due to ongoing replication at later stages of the disease in fatal cases, which implies that the lung damage in these patients is at least propagated by alternative mechanisms, perhaps, an inappropriate immune or stress response.

Bi-Fractal Characterization of the Pore Network of Tight Sandstone

Fluid seepage performance and accumulation in tight sandstone is a critical research topic for in-depth exploration and development, closely related to the heterogeneity of the pore network. The fractal characterization is one of the most compelling and direct ways for quantitative investigation of heterogeneity. However, only one kind of fractal is used in most studies, and the differences and relations between different fractal dimensions are rarely discussed. This paper chose one of the most representative tight sandstone formations in China, the second member of the Xujiahe Formation, as the research object. First, based on physical analysis and XRD analysis, we carried out a qualitative investigation on pore structure utilizing thin-section and scanning electron microscopy. Then, detailed pore structure parameters were obtained using high-pressure mercury intrusion (HPMI). Lastly, we combined two-dimensional fractal analysis on thin-section images and three-dimensional fractal analysis on HPMI data to characterize the pore network heterogeneity quantitatively. The Xu2 tight sandstone is mainly medium- to fine-grained lithic feldspathic sandstone or feldspathic lithic sandstone with low porosity and permeability. Also, the Xujiahe tight sandstone is mainly composed of quartz, feldspar, and clay. The pore types of Xu2 tight sandstones are primarily intergranular pores, micro-fractures, and intra- and intergranular dissolution pores. Moreover, most of the micro-fractures in gas-bearing formation are open-ended, while most are filled by clay minerals in the dry formation. The r50 (median pore radius) is the most sensitive parameter to seepage capability (permeability) and gas-bearing status. The 2D fractal dimension (Ds) of gas-bearing samples is significantly larger than that of dry samples, while the 3D fractal dimension (D1, D2) of gas-bearing samples is lower than that of dry samples. There is a strong negative correlation between D2 and gas-bearing status, permeability, quartz content, and r50, but a positive correlation between Ds and these parameters. D2 represents the heterogeneity of pore space, while the Ds indicates the development of the pore network. Tectonic movements that generate micro-fractures and clay cementation that blocks the seepage channels are the two main controlling factors on fractal dimensions. Combining 2D and 3D fractal analysis could give a more in-depth investigation of pore structure.

An open-access volume electron microscopy atlas of whole cells and tissues.

Understanding cellular architecture is essential for understanding biology. Electron microscopy (EM) uniquely visualizes cellular structures with nanometre resolution. However, traditional methods, such as thin-section EM or EM tomography, have limitations in that they visualize only a single slice or a relatively small volume of the cell, respectively. Focused ion beam-scanning electron microscopy (FIB-SEM) has demonstrated the ability to image small volumes of cellular samples with 4-nm isotropic voxels1. Owing to advances in theprecision and stability of FIB milling, together with enhanced signal detection and faster SEM scanning, we have increased the volume that can be imaged with 4-nmvoxels by two orders of magnitude. Here we present a volume EM atlas at such resolution comprising ten three-dimensional datasets for whole cells and tissues, including cancer cells, immune cells, mouse pancreatic islets and Drosophila neural tissues. These open access data (via OpenOrganelle2) represent the foundation of a field of high-resolution whole-cell volume EM and subsequent analyses, and we invite researchers to explore this atlas andpose questions.

The location of InsP3 receptors in Purkinje cells of murine cerebellum does not supports a direct interaction in the transfer of calcium ions between ER and mitochondria.

The inositol-3-phosphate receptors (IP3Rs) of cerebellar Purkinje cells are located in abundant, large stacks of endoplasmic reticulum (ER) cisternae. Using thin section electron microscopy, we identify very frequent associations of the ER stacks with mitochondria. The associations have two components: a single, close ER-mitochondria contact on one side to the stack, and multiple layers of ER cisternae decorated by IP3Rs receptors on the side away from the mitochondria. Due to their location in the stacks, IP3Rs are never in contact with the mitochondria, although they are in their vicinity. We conclude that transfer of Ca2+ between ER and mitochondria is not directly mediated by IP3Rs, but is based on mitochondrial Ca2+ uptake from the local cytoplasmic spikes during IP3Rs’ activity.

Pore modification mechanisms in a deeply buried non-marine sandstone: The Early Cretaceous Upper Sarir Sandstone Formation, Sirte Basin, Libya

Critical understanding of the reservoir pore-system is crucial for effective fluid-flow. Core-sedimentological description (40 core plugs), petrography (thin section and scanning electron microscopy with energy dispersive spectrometry), x-ray diffractometry, and high-resolution imaging were integrated to characterize pore-modification processes in a deeply buried (ca. 12470–12558 Ft.) non-marine sandstone. The reservoir is dominantly subrounded to subangular, well-sorted to moderately well-sorted, and medium-to fine-grained quartz arenite and lithearenite. Framework ranges from matrix-supported to matrix-devoided types. With a mean point-counted composition of Q95F0L5, quartz is the dominant mineral in all samples. Core-derived porosity and permeability range from 0.88 to 16.89% (Average 9.99%) and ~0.00–431.06 mD (Average 66.42 mD), respectively. Intergranular (ɸI), micro (ɸμ), fracture (CF), and dissolution (Diss) porosities constitute an estimated 60%, 35%, 3%, and 2% of the total porosity. The pore-spaces are randomly distributed and largely disconnected from one another. Connected pores are linked by necking, tubular, and lamellar pore throats. Pore-destructive diagenetic processes occurred mainly in the early-intermediate diagenetic phase, and to lesser extent in the late diagenetic phase. Pore-enhancement processes were of sparse occurrences. Mechanical compaction, quartz overgrowth development, kaolinitization, sideritization, and calcite cementation are the main pore-occluding processes identified. Quartz overgrowth increased with depth and it shows an inverse relationship with poro-perm. The formation of quartz overgrowth haloes in the Upper Sarir Sandstone Formation were most likely formed from non-insitu silica mobilized into the pore system during post-rift cooling. This study confirms the need for careful heterogeneity modelling even in non-marine deposited reservoir sandstone, notwithstanding their known clean nature in contrast to mud-rich marine reservoirs.

Fractal behaviors of NMR saturated and centrifugal T2 spectra in oil shale reservoirs: The Paleogene Funing formation in Subei basin, China

Fluorescence thin section and scanning electron microscopy (SEM) analysis were performed to delineate pore spaces and pore network assemblages of oil shales of Member 2 of Paleogene Funing Formation (E1f2) in Subei Basin, China. Nuclear magnetic resonance (NMR) T2 (transverse relaxation time) spectra were used to gain insight into pore size distribution. Fractal analysis was performed on the NMR T2 spectra measured at saturated and centrifugal status, respectively, with the aim to reveal the different fractal behaviors of irreducible pore realms (centrifugal T2 spectrum) and the entire pore systems (saturated T2 spectrum). Relationships between NMR parameters and fractal dimensions were revealed. The results show that the pore spaces consist of 1) large pore realms including interparticle pores, and microfractures, 2) small pore realms including intragranular dissolution pores, intercrystal micropores and organic matter pores. The T2 spectra are mostly bimodal and left-skewed due to abundance in small pore realms. The right peak or tail distribution is associated with large pore realms. Fractal analysis performed on saturated and centrifugal T2 spectra show that fractal dimensions calculated from centrifugal T2 spectrum are higher. In addition, fractal dimensions for centrifugal T2 spectrum show negative correlation relationships with BVI and T2cutoff values. The different fractal behaviors of saturated and centrifugal T2 spectra reflect the complex pore assemblages in oil shales. The small pore realms determine the microscopic complexity, while large pore realms control the macroscopic reservoir quality of oil shales. However large pore realms (interparticle pores and micro-fractures) are not self-similar with the small pore realms, and can't be described by fractal dimension. Fractal analysis gives insights in the heterogeneous assemblage of pore systems and helps describe complexity of pore structure.

Pore structure characteristics and their influencing factors: A case study from the middle jurassic mixed siliciclastic carbonate rocks, Turpan-Hami basin, Northwest China

The mixed siliciclastic-carbonate rocks of the second member of the Qiketai Formation (J2q2) in the Turpan-Hami Basin are lacustrine tight oil reservoir with vitrinite reflectance values (%, Ro) ranging from 0.64% to 0.81%. X-ray diffraction (XRD), thin sections, field emission scanning electron microscopy (FE-SEM) of argon-milled thin sections, low-temperature N2 adsorption (LNTA), and nuclear magnetic resonance (NMR) analyses were performed to investigate the pore structure characteristics and their influencing factors of the mixed siliciclastic-carbonate reservoirs. The results show that the tight reservoir has a medium-high total organic carbon (TOC) content, and the sedimentary textures include laminated, massive, and intraclasts-rich types. Nanometer scale interparticle pores and microfractures are dominant in the tight reservoirs. The small pores (2–100 nm) make a dominant contribution to the nanoscale storage space according to the comprehensive analysis of the T2 spectra of NMR. Reversed S-shaped isotherms obtained from N2 adsorption are type IV, and hysteresis loops indicate that the shape of pores include slit-or plate-like, ink-bottle-shaped and mixtures of the two. BET surface areas and BJH total pore volume vary from 1.707 m2/g to 8.556 m2/g and 1.13 cm3/100 g to 3.0 cm3/100 g, with an average of 4.31 m2/g and 1.848 cm3/100 g, respectively. The massive and intraclasts-rich rocks have higher NMR porosities, pore sizes and pore volumes than the laminated rocks. Based on the Frenkel-Halsey-Hill model of low-temperature N2 adsorption, the fractal dimensions D1 and D2 are 2.4305–2.7081 and 2.2667–2.6070, respectively. The correlations between the pore structure parameters and the mineralogical composition, TOC content, and fractal dimension reveal that dolomite makes greater contribution to the pore volume and movable fluid saturation than the siliciclastic gains and organic matter, resulting in higher fractal dimensions and more complicated pore structure. In addition, the clay minerals increase pore specific surface area and its complexity in the tight reservoirs. The samples with high silicate mineral and TOC contents tend to contain lower specific surface areas and pore volumes, resulting in lower fractal dimensions and more simplistic pore structure than clay rich samples. Therefore, the complex mineralogical composition, various sedimentary textures and organic matter content all play important roles in the development of pore network.

Morphometry of SARS-CoV and SARS-CoV-2 particles in ultrathin plastic sections of infected Vero cell cultures

SARS-CoV-2 is the causative of the COVID-19 disease, which has spread pandemically around the globe within a few months. It is therefore necessary to collect fundamental information about the disease, its epidemiology and treatment, as well as about the virus itself. While the virus has been identified rapidly, detailed ultrastructural analysis of virus cell biology and architecture is still in its infancy. We therefore studied the virus morphology and morphometry of SARS-CoV-2 in comparison to SARS-CoV as it appears in Vero cell cultures by using conventional thin section electron microscopy and electron tomography. Both virus isolates, SARS-CoV Frankfurt 1 and SARS-CoV-2 Italy-INMI1, were virtually identical at the ultrastructural level and revealed a very similar particle size distribution with a median of about 100 nm without spikes. Maximal spike length of both viruses was 23 nm. The number of spikes per virus particle was about 30% higher in the SARS-CoV than in the SARS-CoV-2 isolate. This result complements a previous qualitative finding, which was related to a lower productivity of SARS-CoV-2 in cell culture in comparison to SARS-CoV.

Variations in ultrasonic wave velocities of Miocene carbonate and clastic sedimentary rocks under dry and fully water saturated conditions

This study investigates the variations in P and S wave velocities (Vp, Vs) under dry and saturated conditions and attempts to develop empirical equations estimating Vs based on Vp. In this context, 48 intact core specimens extracted from the Miocene sedimentary rocks were examined. A significant decrease was observed in Vp under saturated conditions (Vp-sat) for several specimens. Thus, selected samples were further examined by thin section, X-ray diffraction, and scanning electron microscopy equipped with an energy dispersive spectrometer. Correlation analyses were performed to reveal the causes of reduction in Vp-sat in terms of porosity, microcrack density, and mineralogical content. Vs was also observed to have a decreasing trend under saturated conditions. Strength and elasticity loss after saturation were not well correlated with the reduction in Vp-sat. The measured velocity values were also compared with the ones derived from Gassmann’s theory. Despite the discrepancy in the literature, a new parameter explaining the negative difference between the values of saturated and dry Vp was suggested. The mudstone texture and the abundant microporosity were firstly declared to be indicative of a negative velocity difference among the same rock group having similar mineralogy. Afterward, two empirical equations estimating Vs were derived from the ultrasonic wave velocities measured in this study and the data compiled from published literature. These equations were applied to a different dataset and compared with the ones suggested by various researchers. Proposed equations were determined to be more widely applicable and valid for limestone, mudstone, and sandstone samples according to several accuracy metrics.

Nanopore Structure Distribution of the Upper Paleozoic Tight Sandstones and Its Controls on Gas Production Performance in the Shenfu Area, Northeastern Ordos Basin, China.

Based on X-ray diffraction, thin section and scanning electron microscopy observation, helium porosity and permeability tests and high-pressure mercury intrusion experiments, the pore and throat distributions of tight sandstone reservoirs were revealed on a nm-μm scale, and their control on gas productivity in the Shenfu area, northeastern Ordos Basin, China was discussed. The results show that lithic sandstones are the main rock types. As the burial depth increases, the quartz content increases, while the feldspar content decreases. There is approximately 5-25% of interstitial material varying between the different layers, and this interstitial material is mainly composed of mud, kaolinite and Fe-calcite. These tight sandstone reservoirs generally have porosities <10% and permeabilities <1 mD. Except for the Shiqianfeng Formation, the dissolution pores in other Upper Paleozoic strata all account for more than 80% of pores. The main pore types are mainly intragranular dissolution pores, intergranular dissolution pores and cement dissolution pores. Generally, the pore radius is approximately 500 nm, while the pore throats are much smaller are variable in size. Wells with high amounts of sandstones but low gas production rate are generally characterized by dominant intercrystalline pores, few macropores, and low effective porosity. The lithology and reservoir characteristics, which are controlled by primary deposition and secondary diagenesis, are speculated to be main factors controlling the gas contents.

Testing the Phenotypic Effects of a Rab Chimera that Resolves Exchange Factor Specificity from Effector Specificity.

Rab GTPases play key roles in defining the identity of the various compartments that comprise the secretory and endocytic pathways. Recruitment of a Rab to a specific compartment requires its localized activation by a guanine nucleotide exchange factor (GEF). This in turn results in the recruitment of a distinct set of Rab effectors that directs the recognition of the appropriate target compartment by a carrier vesicle and their subsequent fusion. A chimeric Rab protein, Ypt1-SW1Sec4, was found to separate GEF specificity from effector specificity (Grosshans BL, et al. Proc Natl Acad Sci U S A 103(32):11821-11827, 2006), but early studies did not observe strong effects of this allele on growth or membrane traffic (Brennwald P, Novick P. Nature 362(6420):560-563, 1993). To resolve this apparent conundrum, yeast strains expressing the chimeric Rab were subjected to a more extensive battery of phenotypic tests. These tests demonstrated that changing the specificity of the GEF interaction does lead to a change in Rab localization and can lead to the ectopic recruitment of an effector, creating trafficking defects that are dependent upon the level of expression (Grosshans BL, et al. Proc Natl Acad Sci U S A 103(32):11821-11827, 2006). Here we describe the methods used in this analysis. Specifically we describe the following: 1. An assay used to quantify the efficiency of export of a cell wall protein Bgl2, 2. The use of thin section electron microscopy to address the morphology of the secretory machinery, 3. The use of a fluorescently tagged vesicle SNARE protein, GFP-Snc1, to follow plasma membrane recycling and. 4. The use of fluorescently tagged Ypt1 effectors, Cog3-GFP, Uso1-GFP, and Sec7-GFP to follow their recruitment by Ypt1-SW1Sec4.

Quick-Freeze, Deep-Etch Electron Microscopy Reveals the Characteristic Architecture of the Fission Yeast Spore.

The spore of the fission yeast Schizosaccharomyces pombe is a dormant cell that is resistant to a variety of environmental stresses. The S. pombe spore is coated by a proteinaceous surface layer, termed the Isp3 layer because it comprises mainly Isp3 protein. Although thin-section electron microscopy and scanning electron microscopy have revealed the fundamental structure of the spore, its architecture remains unclear. Here we visualized S. pombe spores by using a quick-freeze replica electron microscopy (QFDE-EM) at nanometer resolution, which revealed novel characteristic structures. QFDE-EM revealed that the Isp3 layer exists as an interwoven fibrillar layer. On the spore cell membrane, many deep invaginations, which are longer than those on the vegetative cell membrane, are aligned in parallel. We also observed that during spore germination, the cell surface changes from a smooth to a dendritic filamentous structure, the latter being characteristic of vegetative cells. These findings provide significant insight into not only the structural composition of the spore, but also the mechanism underlying the stress response of the cell.

Characterization of lithofacies in shale oil reservoirs of a lacustrine basin in eastern China: Implications for oil accumulation

The present research study was aimed to identifies the effect of the lithofacies (assemblages) on lacustrine shale oil accumulation, the shale oil layers of the Eocene Shahejie Formation in the Bohai Bay Basin, China, were characterized. The petrological analysis, included core, thin section and scanning electron microscopy observations and X-ray diffraction, indicated that the shale oil layers of the Shahejie Formation are dominated by carbonates, which are characterized by uniform or laminar distributions. The laminar carbonate components were formed through sedimentogenesis or diagenesis. Based on the genesis patterns and the petrology, five major lithofacies (assemblages) were identified in the formation: LF (lithofacies) 1 + 5 is characterized by thin lenticular laminae of crystalline carbonates with black shale; LF2+3 depicts laminae of micritic carbonates with massive lime mudstone; LF3 is a thick layer of massive lime mudstone; LF4 is massive claystone; and LF5 is black shale. The relationship between the lithofacies and the favorability for hosting shale oil reservoirs was investigated using microdrill sampling of the total organic content, reservoir quality analysis, and shale oil-bearing property. In LF1+5, the crystalline carbonates contain abundant interparticle pores, which can act as reservoir spaces, whereas the shale layers have a high potential for hydrocarbon generation. In addition, the hydrocarbon reserves can enter the crystalline carbonates of the assemblage after migrating a short distance. Consequently, LF1+5 is the most favorable assemblage for shale oil accumulation. In addition, LF4 and LF5 have high hydrocarbon generation potentials, and thus a relatively smaller amount of hydrocarbons could accumulate in these assemblages through clay mineral adsorption. Thus, LF4 and LF5 are also valuable sites for shale oil accumulation.

High-resolution analysis of the physicochemical characteristics of sandstone media at the lithofacies scale

Abstract. The prediction of physicochemical rock properties in subsurface models regularly suffers from uncertainty observed at the submeter scale. Although at this scale – which is commonly termed the lithofacies scale – the physicochemical variability plays a critical role for various types of subsurface utilization, its dependence on syndepositional and postdepositional processes is still subject to investigation. The impact of syndepositional and postdepositional geological processes, including depositional dynamics, diagenetic compaction and chemical mass transfer, onto the spatial distribution of physicochemical properties in siliciclastic media at the lithofacies scale is investigated in this study. We propose a new workflow using two cubic rock samples where eight representative geochemical, thermophysical, elastic and hydraulic properties are measured on the cubes' faces and on samples taken from the inside. The scalar fields of the properties are then constructed by means of spatial interpolation. The rock cubes represent the structurally most homogeneous and most heterogeneous lithofacies types observed in a Permian lacustrine-deltaic formation that deposited in an intermontane basin. The spatiotemporal controlling factors are identified by exploratory data analysis and geostatistical modeling in combination with thin section and environmental scanning electron microscopy analyses. Sedimentary structures are well preserved in the spatial patterns of the negatively correlated permeability and mass fraction of Fe2O3. The Fe-rich mud fraction, which builds large amounts of the intergranular rock matrix and of the pseudomatrix, has a degrading effect on the hydraulic properties. This relationship is underlined by a zonal anisotropy that is connected to the observed stratification. Feldspar alteration produced secondary pore space that is filled with authigenic products, including illite, kaolinite and opaque phases. The local enrichment of clay minerals implies a nonpervasive alteration process that is expressed by the network-like spatial patterns of the positively correlated mass fractions of Al2O3 and K2O. Those patterns are spatially decoupled from primary sedimentary structures. The elastic properties, namely P-wave and S-wave velocity, indicate a weak anisotropy that is not strictly perpendicularly oriented to the sedimentary structures. The multifarious patterns observed in this study emphasize the importance of high-resolution sampling in order to properly model the variability present in a lithofacies-scale system. Following this, the physicochemical variability observed at the lithofacies scale might nearly cover the global variability in a formation. Hence, if the local variability is not considered in full-field projects – where the sampling density is usually low – statistical correlations and, thus, conclusions about causal relationships among physicochemical properties might be feigned inadvertently.

Formation mechanism of authigenic chlorite in tight sandstone and its influence on tight oil adsorption, Triassic Ordos Basin, China

In this study, the formation mechanism of authigenic chlorite in tight reservoirs and its influence on the adsorption capacity to tight oil have been analyzed. The occurrence states of chlorite and the formation mechanism have been analyzed by thin section (TS) and field emission scanning electron microscopy (FE-SEM) measurements. Due to the alteration of volcanic rock fragments, the mudstone pressurized water, and the dissolution of early chlorite, the material source has been provided for the formation of chlorite. The formation time of chlorite with different occurrence states is in the following order: grain-coating chlorite → pore-lining chlorite → pore-lining chlorite in dissolved pores → rosette chlorite. Authigenic chlorite developed in the reservoirs has influenced the change of the reservoir quality in two respects. On the one hand, authigenic chlorite can protect the residual pores, improve the anti-compaction capacity of the reservoir, and provide certain inter-crystalline space. On the other hand, it can hinder pore space and inhibit throat, resulting in a decrease in the connectivity of pores and the increase in the heterogeneity of the reservoir. Tight oil absorbed by the chlorite is mainly in the form of the thin film and aggregates. Through in situ testing of environmental scanning electron microscope (ESEM) and energy dispersive spectrum (EDS), the adsorption capacity of chlorite with different occurrence states to tight oil, being in the following order: rosette chlorite &gt; pore-lining chlorite &gt; pore-lining chlorite in dissolved pores &gt; grain-coating chlorite. Furthermore, the controlling factors on reservoir quality, the content of chlorite and content of Fe and K have been investigated, and the adsorption capacity of different chlorite types has been studied, which can provide guidance for analysis of the control factors on the difference in adsorption capacity of different occurrence states of chlorite to tight oil in tight reservoirs.

Sedimentological and geochemical characterization of the Upper Permian transitional facies of the Longtan Formation, northern Guizhou Province, southwest China: Insights into paleo-environmental conditions and organic matter accumulation mechanisms

Characterized by high TOC content and large cumulative thickness, the Upper Permian marine-continental transitional facies of shales are widely distributed in southwest China, and are currently becoming a prospective area for shale gas exploration and production. Compared to marine shales, the organic matter (OM) accumulation model and paleo-environmental conditions remain unclear in transitional settings. In this study, core descriptions, thin section and scanning electron microscopy (SEM) observations, X-ray diffraction (XRD) mineralogical analysis, and a major, trace, and rare earth element analysis were integrated to document the varying lithofacies, paleo-environmental conditions, and OM accumulation mechanisms for the Upper Permian transitional facies of the Longtan Formation in northern Guizhou Province, southwest China.Six major lithofacies, including carbonaceous mudstones, siliceous-clay mixed mudstones, argillaceous mudstones, silty shales, muddy siltstones, and calcareous-clay mixed shales, were identified. The XRD analysis and SEM images suggest that clay (average = 51.2 wt%) and siderite (average = 17.3 wt%) are the dominant minerals in the Longtan Formation, which is different from the mineralogical composition of typical marine shales, which are generally dominated by quartz (e.g. Horn River Shale in the Western Canada Sedimentary Basin, and the Barnett Shale in the Fort Worth Basin). Furthermore, the sedimentological and geochemical analyses suggest that the paleo-environmental conditions and OM accumulation mechanisms of the transitional facies of the Longtan Formation are different from those of marine shales, and can be summarized as follows: (1) terrestrial plant fragments mainly contribute to the TOC contents of the Longtan Formation; (2) paleoproductivity is generally the major influencing factor of OM accumulation in marine shales, but is relatively low during the deposition of the Longtan Formation; (3) terrestrial OM input, redox conditions and sedimentation rate are the major factors controlling OM accumulation; and (4) most of the silica content has detrital origin instead of biogenic origin in the Longtan Formation.