Abstract Soft rock has the characteristics of poor engineering mechanics, and it is easy to change under the action of water or external load. This paper uses the pulse attenuation permeability meter to develop permeability test and coefficient of variation for weak rock with common engineering mechanical properties. Calculate and explore the geological stress sensitivity characteristics of weak rock engineering within the Three Gorges reservoir area. The conclusions are as follows: the permeability of weak rock in the Three Gorges reservoir area is less than 0.1mD, which belongs to the type of compact soft rock, among which the permeability of medium sandstone (0.048mD)> the permeability of fine sandstone (0.0055mD)> the permeability of mud shale (0.0047mD); the rock permeability coefficient of variation is greater than 0.7, with a strong heterogeneity. The permeability of soft rock has obvious anisotropy. The permeability of the vertical layer of medium-fine sandstone and silty mudstone is greater than the permeability parallel to the plane. The difference between the two is closely related to the physical difference between different lithologies. The permeability of siltstone, shale and sandstone rocks decreases exponentially with the increase of effective stress. The relationship between the permeability loss rates of various types of rock is: shale> siltstone> sandstone, indicating the same stress condition, page Rocks have higher stress sensitivity than siltstones and sandstones. This is mainly because the fractures in sandstone and siltstone are more developed than shale.
Among the various shale reservoir evaluation methods, the scanning electron microscope (SEM) image method is widely used. Its image can intuitively reflect the development stage of a shale reservoir and is often used for the qualitative characterization of shale pores. However, manual image processing is inefficient and cannot quantitatively characterize pores. The semantic segmentation method of deep learning greatly improves the efficiency of image analysis and can calculate the face rate of shale SEM images to achieve quantitative characterization. In this paper, the high-maturity shale of the Longmaxi Formation in the Changning area of Yibin City, Sichuan Province, and the low-maturity shale of Beibu Gulf Basin in China are studied. Based on the Pore-net network model, the intelligent identification and quantitative characterization of pores in shale SEM images are realized. The pore-net model is improved from the U-net deep-learning network model, which improves the ability of the network model to identify pores. The results show that the pore-net model performs better than the U-net model, FCN model, DeepLab V3 + model, and traditional binarization method. The problem of low accuracy of the traditional pore identification method is solved. The porosity of SEM images of high-maturity shale calculated by the pore-net network model is between 12 and 19% deviation from the experimental data. The calculated porosity of the SEM image of the low-maturity shale has a large deviation from the experimental data, which is between 14 and 47%. Compared with the porosity results calculated by other methods, the results calculated by pore-net are closer to the true value, which proves that the porosity calculated by the pore-net network model is reliable. The deep-learning semantic image segmentation method is suitable for pore recognition of shale SEM images. The fully convolutional neural network model is used to train the manually labeled shale SEM images, which can realize the intelligent recognition and quantitative characterization of the pores in the shale SEM images. It provides a certain reference value for the evaluation of shale oil and gas reservoirs and the study of other porous materials.
The Three Gorges Reservoir area of the Yangtze River has formed vast riverine fallout zones as a result of its periodic water storage and flood discharge operations, and the main constituents of this area are quaternary loose clays. It is important to study the microscopic characteristics of clay minerals in these fallout zones and their adsorption properties of Hg2+ to guide the environmental safety of the fallout zones in the Three Gorges Reservoir area. In this context, the authors of this paper used X-ray diffraction (XRD) experiments to reveal the main clay mineral compositions in the fallout zones and then constructed the molecular model structures of the clay minerals based on molecular dynamics theory and studied the adsorption characteristics of these clay minerals with Hg2+ in depth. The results show that the main clay minerals in the Three Gorges Reservoir area fallout zone include illite, illite-mixed layer and green-mixed layer, in which the content of illite ranges from 21% to 54%. Taking illite as the study object, the heat of adsorption of Hg2+ in illite ranged from 14.83 kJ·mol−1 to 31.92 kJ·mol−1, which is a physical adsorption. The heat of adsorption was mainly affected by the water content and had little relationship with temperature. With the gradual increase in water content, the heat of adsorption gradually decreases. The adsorption amount of Hg2+, on the other hand, is jointly affected by water content and temperature and decreases with the increase in water content and temperature; under natural environmental conditions (P = 0.1 Mpa), the adsorption characteristics of Hg2+ in illite change with the change in water content. When the water content was between 0% and 6.95%, the increase in water content led to an increase in the interlayer spacing of illite, and the adsorption of Hg2+ in illite was in a monolayer state, with the adsorption peaks located from 4.5~5.5 Å. When the water content increased to 6.95% to 13.90%, the layer spacing of illite reached the maximum, and the adsorption of Hg2+ in illite transitioned from a monolayer to a bilayer, with the adsorption peaks located between 5 Å and 9~10 Å, respectively. When the water content was further increased to 13.90% to 20.85%, the increase in water content instead led to a slight decrease in the layer spacing of illite, showing a tendency of transitioning from a bilayer to a monolayer adsorption layer, which at the same time changed the number of adsorption layers of Hg2+; the study also revealed that the interaction between illite and Hg2+ was regulated by van der Waals and Coulomb forces, whereas the increase in temperature promoted the Hg2+ +diffusion, and an increase in water content inhibits the diffusion of Hg2+. In summary, these findings provide valuable theoretical support for solving the problem of Hg2+ pollution in the Three Gorges Reservoir Decline Zone.
In order to study the adsorption process and adsorption characteristics of shale oil at the macro scale, the isothermal adsorption experiments of illite and kerogen on heptadecane (oil phase) solution were carried out by infrared spectrophotometry and gas chromatography-mass spectrometry. The reaction mechanism of alkane solution concentration and temperature in the adsorption process was investigated. The adsorption characteristics of heptadecane on the surface and pores of illite and kerogen were elucidated by adsorption isotherm model and adsorption thermodynamic model. The results show that: The concentration of alkane solution contributes to the adsorption of illite and kerogen. As the concentration of the solution continues to increase, the adsorption rate gradually slows down. However, the temperature hardly affects the adsorption rate. At 25℃, 50℃ and 60℃, the adsorption process of illite on alkane solution is more consistent with Langmuir model and Freundlich model, respectively. The difference is that Langmuir model is suitable for describing the whole adsorption process of kerogen on alkane solution. 3) The adsorption process of illite and kerogen to heptadecane solution is an endothermic reaction. Heating helps to accelerate the migration rate of alkanes, which is conducive to the adsorption reaction. The research results clarify the adsorption characteristics of shale oil heavy components from the macro level, and fill the research gap in the application of solid-liquid isothermal adsorption physical experiments to the adsorption and occurrence of shale oil.
Using one or two electric dipole transmitters in the Controlled source electromgnetic method, this paper calculate the transient electromagnetic responses of one and two 3D conductive anomalous bodies in the layered earth by varying the number and intensity of the dipole sources. The results of the models show that satisfactory resolution can be achieved when only one dipole source is used. The stronger the intensity of the electric dipole source, the better resolution for the anomalous body for the same offset. When two electric dipole transmitters laid each side of one 3D body, it means that the anomalous body locates in the middle of the sources and the resolution to the target becomes poor. The numerical results of the transient electromagnetic responses of two 3D bodies also support the idea that resolution is not good when two transmitters are used in each side of the targets simultaneously. As the conclusion, in order to get good resolution to the target, multi transmitters laid different side of the geological target should not be used the same time in the field survey.
Quasi-bound states in the continuum (QBIC), with exceptionally high- Q factors and the local field enhancement effect, have found potential applications in matter sensing. Introducing the QBIC mechanism into terahertz (THz) metasurfaces can significantly enhance the interaction between incident THz waves and matter, providing a feasible platform for the detection of biochemical substances. Currently, most experimental studies on terahertz QBIC metasurfaces utilize metallic structures. By contrast, research on terahertz all-dielectric QBIC metasurfaces generally remains at the simulation stage due to the high fabrication process requirements, and transitioning to the experimental stage still poses many challenges. In this paper, a hollow-structured all-silicon metasurface supporting THz QBIC is proposed. The resonance of THz QBIC is excited via a simple hollow structure and observed in experiment. Simulations and experimental results demonstrated that the designed THz QBIC metasurface can achieve sensing of Auramine O. Notably, it is the first study, to our knowledge, to employ a metasurface to sense Auramine O. Additionally, the sensing performance maintains good stability under different humidity and temperature conditions. This study provides new references and insights for the design and implementation of THz QBIC, and also opens a new pathway for the detection of Auramine O.
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