Search Results (42)

Carbonate rock slopes in reservoir environments are increasingly exposed to dissolution-induced deterioration due to water level fluctuations. However, the influence of internal structures—particularly calcite veins—on dissolution behavior remains inadequately understood. The acid-induced dissolution of limestone by a sulfuric acid solution leads to the removal of soluble minerals and changes to the rock structure. Natural variation in rock structures—particularly in the presence, density, and morphology of calcite veins—can significantly affect the dissolution process and its outcomes. In this study, we obtained three types of Triassic limestone from the same host rock but with varying vein structures from the Three Gorges Reservoir area. Cylindrical rock specimens were prepared to investigate the acid-induced dissolution behavior of limestone in a sulfuric acid solution. We identified and analyzed the macrostructures on the rock specimens before and after the interaction. Additionally, SEM was employed to observe the microstructures of the specimens before and after the acid-induced dissolution, and fractal dimension analysis was conducted on the SEM images to quantify surface complexity. Furthermore, we used a focused ion beam–scanning electron microscope (FIB-SEM) with an automatic mineral identification and characterization system, as well as mineral roundness calculation, for mineral identification and analysis. Based on the experiments and analyses, we determined the following: The contact surfaces between the host rock and the calcite veins increase the dissolution areas between the limestone and the sulfuric acid solution, intensifying the dissolution reactions, enhancing the connectivity of the original microstructural planes, and generating new, highly extended dissolution fissures. The calcite veins facilitate the entry of sulfuric acid solution into the limestone, intensifying the dissolution of the edges and corners of dolomite and resulting in the gradual rounding of dolomite shapes. Quantitatively, the limestone with dense, fine calcite veins exhibited the most severe dissolution, with water absorption rates nearly twice as high as the non-veined samples (0.13% vs. 0.07%), a 2.2% reduction in fractal dimension, and a 19.53% increase in dolomite roundness with the 1 ≤ R ≤ 3 interval, indicating significantly enhanced surface complexity and mineral reshaping. In summary, the presence of more calcite veins, regardless of their width, leads to more severe rock dissolution. Full article

This study investigates the microscopic structural changes and the evolution of physical properties in typical shale samples from three wells in southwestern China during water–rock interactions. Using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and other techniques, we analyzed the changes in pore structure, mineral dissolution behavior, and fracture propagation in shale samples of different types (organic-rich, mixed, and inorganic) during water immersion. The results show that water–rock interaction significantly affects the porosity, fracture width, and physical properties of shale. As the reaction time increases, the pore volume and number of pores generally increase in all shale types, with significant fracture propagation. Furthermore, fracture width changes exhibit varying trends depending on the reaction depth. NMR T2 spectrum analysis indicates that water–rock interaction not only influences the expansion of microfractures but also shows different responses in organic and inorganic pores. SEM images further reveal the impact of water–rock interaction on mineral dissolution, particularly during the early stages, where the dissolution of minerals significantly alters the pore structure. Overall, water–rock interaction plays a crucial role in the development of shale gas reservoirs, providing valuable data and theoretical support for future shale gas extraction. Full article

The tight sandstone reservoirs within the Oligocene Huagang Formation represent one of the most promising exploration targets for future hydrocarbon development in the Xihu Depression of the East China Sea Basin. The reservoir has complex sedimentary and diagenetic processes. In this paper, a variety of methods, such as microscopic image observation, particle size analysis, X-ray diffraction measurement (XRD), heavy minerals, carbon and oxygen isotopes of cement, the homogenization temperature of fluid inclusions, zircon (U-Th)/He isotopes, and high-pressure mercury intrusion (HPMI), are used to analyze the thermal evolution history, diagenetic evolution process, and the causes of differences in diagenetic processes and high-quality reservoirs. This study shows that the provenance of the southern region is derived from western metamorphic rock, while that of the northern region is dominated by northern metamorphic rock, including some eastern volcanic rock. The northern region exhibits a stronger compaction and lower porosity, primarily due to a greater proportion of volcanic rock provenance. Additionally, coarse-grained lithofacies exhibit a higher quartz content and lower proportions of clay minerals and lithic fragment compared to fine-grained lithofacies, consequently demonstrating greater resistance to compaction. The Huagang Formation reservoir has three stages of carbonate cementation, two stages of quartz overgrowth, and two stages of fluid charging. The two stages of fluid charging correspond to two stages of organic acid dissolution. In the northern region, the geothermal gradient is high, and the burial depth is large, so the diagenetic event occurred earlier and is now in the mesodiagenesis B stage, while in the southern region, the geothermal gradient is low, and the burial depth is small and is now in the mesodiagenesis A stage. The southern distributary channel sands and northern high-energy braided channel sands constitute high-quality reservoirs, characterized by a coarse grain size, large pore throats, and minimal cement content. Full article

This study presents a novel lithological analysis method that combines optical thin-section analysis with intelligent algorithms. The method utilizes mineral composition data and two-dimensional rock properties to improve the accuracy and efficiency of lithological identification. By integrating high-resolution optical imaging to precisely capture microscopic rock textures with automated mineral composition analysis systems, this method ensures the rapid and accurate identification of major mineral components without sample damage. Furthermore, advanced image processing and similarity analysis algorithms effectively classify and automatically identify distinct rock layers, enabling a continuous and precise lithological identification process. This approach overcomes the limitations of traditional methods, including subjectivity and inefficiency, and provides robust technical support for geological exploration and mineral resource evaluation. The study shows that this method markedly improves the efficiency of petrological analysis compared to traditional logging techniques. The spatial resolution for mineral composition and lithological identification improved from 12.5 cm to 7 cm per point, maintaining an accuracy of 83%. These results underscore the method’s potential to advance technologies in geoscience and related fields. Full article

Reservoir space characteristics are the key to reservoir evaluation and the evaluation of reservoir capacity. The reservoir space of fracture-vuggy carbonate reservoirs is complex and diverse, and it develops from micro to macro. There is a lack of systematic study on the reservoir space of the Ordovician fracture-vuggy carbonate reservoir. Therefore, taking the Ordovician Yijianfang Formation in Yueman Block of Fuman Oilfield in Tarim Basin as an example, the microscopic reservoir space characteristics of the study area were characterized by rock thin section identification, X-ray diffraction, scanning electron microscopy, high-pressure mercury injection, and low-temperature nitrogen adsorption experiments, and the macroscopic reservoir space characteristics of the study area were characterized by core observation, drilling and logging data, and imaging logging data. The results showed that (1) the lithology of the Ordovician Yijianfang Formation in the Yueman area of Fuman Oilfield is mainly micrite and sparry grain limestone. The mineral composition is mainly calcite, accounting for 97.35%, containing a small amount of quartz and dolomite, accounting for 1.1% and 1.55%, respectively. (2) At the micro level, the reservoir space of Yijianfang Formation in Yueman Block is not developed in primary pores, mainly having developed dissolution pores, structural fractures, and pressure solution fractures, and the pore size is distributed from the nanometer to micron scale. (3) The dissolution caves in the study area are developed at the macro level, mainly including pore-type, cave-type, fracture-pore-type, and fracture-type reservoirs. The research results provide technical support for the accurate evaluation of fractured-vuggy carbonate reservoirs and the improvement of exploration and development effects. Full article

The mechanical characterization of carbonate rock is crucial for the development of a hydrocarbon reservoir and underground gas storage. As a kind of natural composite material, the mechanical properties of carbonate rock exhibit multiscale characteristics. The macroscopic mechanical properties of carbonate rock are determined by the mineral composition and structure at the micro scale. To achieve a mechanical investigation at the micro scale, this study designed a scheme for micromechanical characterization of carbonate rock. First, scanning electron microscope observation and energy dispersive spectroscopy analysis were combined to select the appropriate micromechanical test areas and to identify the mineral types in each area. Second, the selected test area was positioned in the nanoindentation instrument through the comparison of different-type microscopic images. Finally, quasi-static nanoindentation was carried out on the surface of different minerals in the selected test area to obtain quantitative mechanical evaluation results. A typical carbonate rock sample from the Huangcaoxia gas storage was investigated in this study. The experimental results indicated apparent micromechanical heterogeneity in the carbonate rock. The Young’s modulus of pyrite was over 200 GPa, while that of clay minerals was only approximately 50 GPa. In addition, the proposed micromechanical characterization scheme was discussed based on experimental results. For minerals with an unknown Poisson’s ratio, the maximum error introduced by the 0.25 assumption was lower than 15%. To discuss the effectiveness of the nanoindentation results, the characterization abilities constituted by lateral spatial resolution and elastic response depth were analyzed. The analysis results revealed that the nanoindentation measurement of clay was more susceptible to influence by the surrounding environment as compared to other kinds of minerals with the experimental setup in this study. The micromechanical characterization scheme for clay minerals can be optimized in future research. The mechanical data obtained at the micro scale can be used for the interpretation of the macroscopic mechanical features of carbonate rock for the parameter input and validation of mineral-related simulation and for the construction of a mechanical upscaling model. Full article

As a potential strategic mineral resource, lithium (Li) in coal measures (including coal and parting) has attracted increasing attention from scholars globally. For a long time, Li in coal measures has been studied mainly on the macro-scale (whole rock); however, the microscopic characteristics of Li and Li isotope variations in coal measures are less well known. In this study, the No. 6 coal measures in the Haerwusu Mine were studied using ICP-MS, XRD, SEM-EDS, MC-ICP-MS, and LA-ICP-MS. The geochemical and mineralogical characteristics, the microscale distribution of Li in minerals, and the Li isotopes of Li-rich coal and parting in the No. 6 coal measure were investigated. The results show that the Li content in the No. 6 coal seam ranges from 3.8 to 190 μg/g (average 83 μg/g), which is lower than the parting (290 μg/g) and higher than the comprehensive evaluation index of Li in Chinese coal (80 μg/g). LA-ICP-MS imaging showed that Li in the coal is mainly contained within cryptocrystalline or amorphous lamellae aluminosilicate materials, and the Li content in lenticular aggregate kaolinite is low. The Li in parting is mainly found in illite/chlorite. The δ⁷Li of the coals was 3.86‰, which may be influenced by the input of the source rock. The δ⁷Li of the parting (7.86‰), which was higher than that of the coal, in addition to being inherited from the source rock, was also attributed to the preferential adsorption of ⁷Li by the secondary clay minerals entrapped in the parting from water during diagenetic compaction. Finally, by integrating the peat bog sediment source composition, sedimentary environment evolution, and Li isotope fractionation mechanism of No. 6 coal, a Li metallogenic model in the Li-rich coal measure was initially established. In theory, the research results should enrich the overall understanding of the Li mineralization mechanism in coal measures from the micro-scale in situ and provide a scientific basis for the comprehensive utilization of coal measure resources. Full article

This work studies enhancing the capabilities of compact laser spectroscopes integrated into space-exploration rovers by adding 3D topography measurement techniques. Laser spectroscopy enables the in situ analysis of sample composition, aiding in the understanding of the geological history of extraterrestrial bodies. To complement spectroscopic data, the inclusion of 3D imaging is proposed to provide unprecedented contextual information. The morphological information aids material characterization and hence the constraining of rock and mineral histories. Assigning height information to lateral pixels creates topographies, which offer a more complete spatial dataset than contextual 2D imaging. To aid the integration of 3D measurement into future proposals for rover-based laser spectrometers, the relevant scientific, rover, and sample constraints are outlined. The candidate 3D technologies are discussed, and estimates of performance, weight, and power consumptions guide the down-selection process in three application examples. Technology choice is discussed from different perspectives. Inline microscopic fringe-projection profilometry, incoherent digital holography, and multiwavelength digital holography are found to be promising candidates for further development. Full article

The nephrite belt in the Altun Mountain–Western Kunlun Mountain region, which extends about 1300 km in Xinjiang, NW China, is the largest nephrite deposit in the world. The Qiemo region in the Altun Mountains is a crucial nephrite-producing area in China, with demonstrated substantial prospects for future exploration. While existing research has extensively investigated secondary nephrite deposits in the Karakash River and native black nephrite deposits in Guangxi Dahua, a comprehensive investigation of black nephrite from original deposits in Xinjiang is lacking. Margou black-toned nephrite was recently found in primary deposits in Qiemo County, Xinjiang; this makes in-depth research on the characteristics of this mine necessary. A number of technical analytical methods such as polarizing microscopy, Ultra-Deep Three-Dimensional Microscope, electron microprobe, back-scattered electron image analysis, X-ray fluorescence, and inductively coupled plasma mass spectrometry were employed for this research. An experimental test was conducted to elucidate the chemical and mineralogical composition, further clarifying the genetic types of the black and black cyan nephrite from the Margou deposit in Qiemo, Xinjiang. The results reveal that the nephrite is mainly composed of tremolite–actinolite, characterized by Mg/(Mg + Fe²⁺) ratios ranging from 0.86 to 1.0. Minor minerals include diopside, epidote, pargasite, apatite, zircon, pyrite, and magnetite. Bulk-rock rare earth element (REE) patterns exhibit distinctive features, such as negative Eu anomalies (δEu = 0.00–0.17), decreasing light REEs, a relatively flat distribution of heavy REEs, and low total REE concentrations (1.6–38.9 μg/g); furthermore, the Cr (6–21 μg/g) and Ni (2.5–4.5 μg/g) contents are remarkably low. The magmatic influence of granite appears to be a fundamental factor in the genesis of the magnesian skarn hosting Margou nephrite. The distinctive black and black cyan colors are attributed to heightened iron content, mainly associated with FeO (0.08~6.29 wt.%). Analyses of the chemical composition allow Margou nephrite to be classified as typical of magnesian skarn deposits. Full article

Nephrite is a very precious gemstone material. As a non-renewable resource, the discovery of new nephrite deposits and the study of the genesis of nephrite have aroused great interest. A new occurrence of nephrite known as Xinyu nephrite was discovered in Xinyu Country, Jiangxi province, China. Field investigations reveal that nephrite appears in a contact zone between the Mengshan composite granitic pluton and Permian carbonate rock. The carbonate rock is calcic marble that underwent diopsidization and tremolitization. Nephrites have a light yellow-green color, weak greasy luster, are slightly-translucent to translucent, and are fine-grained. Their refractive index (RI) ranges from 1.60 to 1.61, and their specific gravity (SG) value ranges from 2.90 to 2.91, falling within the range of nephrites from Xinjiang, China. Their Mohs hardness (Hm) ranges from 5.78 to 5.83. Petrographic observations and electron probe micro analyzer (EPMA) data indicated that analyzed nephrites mainly comprise tremolite, with minor diopside, calcite, quartz, and apatite. Tremolite has a ratio of Mg/(Mg + Fe²⁺) greater than 0.99. The tremolite grains show microscopic fibrous-felted and columnar textures. Scanning electron microscope (SEM) images show some tremolite fibers interwoven in different crystallographic orientations, and some arranged in parallel. Fourier transform infrared and Raman spectroscopy features reveal the bands of minerals typical for nephrite composition. The petrographic characteristics and geological background of the Mengshan area indicate that nephrite formed through a replacement of calcic marble, which differs from the two known types (D-type: dolomite-related; S-type: serpentinite-related). Mineral replacements were common in nephrite, including diopside by tremolite, calcite by tremolite, and recrystallization of coarse by fine tremolite grains. The discovery of Xinyu nephrite occurrence complements the resource and provides an updated case for the in-depth study of the diversity of nephrite deposits. Full article

The Wadi Samra–Wadi Kid district in southeastern Sinai, Egypt, has undergone extensive investigation involving remote sensing analysis, field geology studies, petrography, and geochemistry. The main aim of this study is the integration between remote sensing applications, fieldwork, and laboratory studies for accurate lithological mapping for future mineral exploration in the study region. The field relationships between these coincident rocks were studied in the study area. Landsat-8 (OLI) data that cover the investigated area were used in this paper. The different rock units in the study area were studied petrographically using a polarizing microscope, in addition to major and trace analysis using ICP-OES tools. The Operational Land Imager (OLI) images were used with several processing methods, such as false color composite (FCC), band ratio (BR), principal component analysis (PCA), and minimum noise fraction (MNF) techniques for detecting the different types of rock units in the Wadi Kid district. This district mainly consists of a volcano-sedimentary sequence as well as diorite, gabbro, granite, and albitite. Geochemically, the metasediments are classified as pelitic graywackes derived from sedimentary origin (i.e., shales). The Al₂O₃ and CaO contents are medium–high, while the Fe₂O₃ and TiO₂ contents are very low. Alkaline minerals are relatively low–medium in content. All of the metasediment samples are characterized by high MgO contents and low SiO₂, Fe₂O₃, and CaO contents. The granitic rocks appear to have alkaline and subalkaline affinity, while the subalkaline granites are high-K calc-alkaline to shoshonite series. The alkaline rocks are classified as albitite, while the calc-alkaline series samples vary from monzodiorites to granites. The outcomes of this study can be used for prospecting metallic and industrial mineral exploration in the Wadi Kid district. Full article

Spectral unmixing of geological mixtures, such as rocks, is a challenging inversion problem because of nonlinear interactions of light with the intimately mixed minerals at a microscopic scale. The fine-scale mixing of minerals in rocks limits the sensor’s ability to identify pure mineral endmembers and spectrally resolve these constituents within a given spatial resolution. In this study, we attempt to model the spectral unmixing of two rocks, namely, serpentinite and granite, by acquiring their hyperspectral images in a controlled environment, having uniform illumination, using a laboratory-based imaging spectroradiometer. The endmember spectra of each rock were identified by comparing a limited set of pure hyperspectral image pixels with the constituent minerals of the rocks based on their diagnostic spectral features. A series of spectral unmixing paradigms for explaining geological mixtures, including those ranging from simple physics-based light interaction models (linear, bilinear, and polynomial models) to classification-based models (support vector machines (SVMs) and half Siamese network (HSN)), were tested to estimate the fractional abundances of the endmembers at each pixel position of the image. The analysis of the results of the spectral unmixing algorithms using the ground truth abundance maps and actual mineralogical composition of the rock samples (estimated using X-ray diffraction (XRD) analysis) indicate a better performance of the pure pixel-guided HSN model in comparison to the linear, bilinear, polynomial, and SVM-based unmixing approaches. The HSN-based approach yielded reduced errors of abundance estimation, image reconstruction, and mineralogical composition for serpentinite and granite. With its ability to train using limited pure pixels, the half-Siamese network model has a scope for spectrally unmixing rock samples of varying mineralogical composition and grain sizes. Hence, HSN-based approaches effectively address the modelling of nonlinear mixing in geological mixtures. Full article

Since each rock type represents different deformation characteristics, prediction of the damage beforehand is one of the most fundamental problems of industrial activities and rock engineering studies. Previous studies have predicted the stress–strain behaviors preceding rock failure; however, quantitative analyses of the progressive damage in different rocks under stress have not been accurately presented. This study aims to quantify pre-failure rock damage by investigating the stress-induced microscale cracking process in three different rock types, including diabase, ignimbrite, and marble, representing strong, medium-hard, and weak rock types, respectively. We demonstrate crack intensity at critical stress levels where cracking initiates (σ_ci), propagates (σ_cd), and where failure occurs (σ_peak) based on scanning electron microscope (SEM) images. Furthermore, the progression of rock damage was quantified for each rock type through the fractal analyses of crack patterns on these images. Our results show that the patterns in diabase have the highest fractal dimensions (D_B) for all three stress levels. While marble produces the lowest D_B value up to σ_ci stress level, it presents greater D_B values than those of ignimbrite, starting from the σ_cd level. This is because rock damage in ignimbrite is controlled by the groundmass, proceeding from such stress level. Rock texture controls the rock stiffness and, hence, the D_B values of cracking. The mineral composition is effective on the rock strength, but the textural pattern of the minerals has a first-order control on the rock deformation behavior. Overall, our results provide a better understanding of progressive damage in different rock types, which is crucial in the design of engineering structures. Full article

The exploration and development of Gulong shale oil in the Songliao Basin has achieved a major breakthrough, with the result that a national shale oil demonstration area is being built. The shale in the Sanzhao Sag is abundant in organic matter and is an important replacement area. For this reason, it has recently become a focus for research and exploration. Compared with the Gulong Sag, the Qingshankou Formation in the Sanzhao Sag is relatively immature, and comparatively little is known about its pore structure. For this study, well ZY1, a key well in the Sanzhao Sag, was selected as the research object. Thin section observation, high-resolution field emission scanning electron microscopy, Modular Automated Processing Systemimaging, X-ray diffraction of whole rock and clay, TOC pyrolysis, and Low-pressure N₂ adsorption were used to investigate the pore structure in the sag to determine the factors influencing pore development. The principal understandings are as follows: (1) The Qingshankou Formation in the Sanzhao Sag is predominantly clay shale, with a high content of clay minerals (32.8 to 70%) and TOC contents of 0.7 to 11%. These values indicate good hydrocarbon generation potential. (2) Interparticle pores, intraparticle pores, and organic matter pores are developed. Intergranular pores are the main type, mostly observed between granular minerals or between granular minerals and clays. Intraparticle pores are observed in pyrite mass and dissolved unstable minerals. Organic matter pores (OMP) occur in primary organic matter and migrate into solid bitumen. (3) The shale pores in the Sanzhao Sag are mainly H3-type slit pores, with specific surface areas of 5.4~22.9 m²/g and pore volumes of 0.03~0.07 cm³/g. Mesopores make the largest contribution to pore volume and specific surface area. Scanning electron microscope (MAPS) imaging shows that the pore size distribution of shale is mainly 20~30 nm and 100~200 nm and that large pores, especially pores of 100~200 nm and 1~2 μm, make the largest contribution to the facies. (4) The pore structure in the Sanzhao Sag is affected by mineral composition, abundance of organic matter, thermal evolution degree, and diagenesis. Organic-inorganic interactions influence and determine the pore structure characteristics of the Qingshankou Formation shale. This paper is intended to provide scientific guidance and technical support for evaluating the effectiveness of shale oil reservoirs and selecting sweet spots in the Sanzhao Sag. Full article

The Lower Cretaceous reservoir core samples from the upper part of Qamchuqa Formation, Baba Dome, Kirkuk Oil Company, show evidence for multistage episodes of dolomitization and a complex diagenetic history. Optical microscope reveals muti-phase of diagenesis: an early stage of diagenesis and its alteration, later, by evaporated seawater under near-surface setting conditions, followed by different event of dolomitization. The stylolite microstructures postdate anhydrite and early matrix dolomite crystals (DI) and predated the coarse rhombohedral (DII) and saddle dolomite crystals (SD), which were formed under a deep burial realm. High-resolution data from stable isotopes integrated with intensive optical observation, ImageJ software, and litho-log are utilized to establish a qualified methods for mapping a better image of hydrothermal diagenesis under subsurface conditions. These methods revealed different types of dolomites, mostly focused on fractures and void spaces, and the paragenetic sequence shows the complex history of diagenetic carbonate rocks hosted in the limestone of Qamchuqa Formation. The sequence is started from older to younger as follow: Micritization, early anhydrite mineral formation, early dolomite, stylolization, rhombohedral dolomite, and saddle dolomite crystals. The early dolomite phase is usually corroded by hydrocarbon phase, and, geometrically, the hydrocarbon phase is overgrown by the early dolomite. Therefore, the dolomitizing fluids enhanced the porosity system and had positive impact on the hydrocarbon movement. This phase of dolomite and anhydrite formation were associated with the first groups of δ¹⁸OVPDB and δ¹³CVPDB data, a narrow range of oxygen values, and inverse Js of Lohmann curve fits towards the near-surface and shallow diagenetic settings. Detailed optical microscope and supportive data from oxygen-carbon isotopes of saddle dolomite confirm the presence of hot fluids under subsurface condition. The latter data were supported by light δ¹⁸OVPDB and constant heavy δ¹³CVPDB, which indicates a hot fluid possibly circulated in deep burial conditions, and this is channeled along the fracture and pore spaces, consistent with hydrocarbon migration. These pore spaces influenced by leaching were hydrocarbon migrations associated with hot fluids under deep sitting conditions. However, a remarkable part of pristine microfacies of host limestone was preserved. In summary, this study will add a new understanding and insight into the origin, genesis, and timing of these dolomites and their direct connection to hydrocarbon exploration and development in most reservoir oil rocks, which are exposed to hydrothermal fluids. Additionally, the study adds new data on hydrothermal fluids in subsurface conditions, whereas most of the previous reported work has mostly focused on exposed rock. Full article