Journal of Energy Engineering

Oil shale is a potential strategic resource with large reserves and widespread application potential, and in situ combustion is an effective method to exploit oil shale. However, the interaction mechanism between pyrolysis and combustion reaction is still not clear; hence, the evolution of components and temperature in the reservoir is hard to describe, limiting the application of in situ combustion in oil shale. In this paper, we established a comprehensive reactive flow model to describe the in situ combustion in oil shale, and the in situ combustion process is analyzed in detail. During the in situ combustion, only pyrolysis reactions occur in the matrix system, while combustion reactions only occur in the fracture system. Under the interaction mechanisms of these two kinds of chemical reactions, in situ combustion upgrading can be carried out continuously. The produced oil and hydrocarbon gas per unit volume of oil shale are $0.06{\mathrm{m}}^3/{\mathrm{m}}^3$ and $12.5{\mathrm{m}}^3/{\mathrm{m}}^3$, respectively, but about $83.3{\mathrm{m}}^3/{\mathrm{m}}^3$ of ${\mathrm{CO}}_2$ is produced that needs to be stored subsequently when air is directly injected into the reservoir to maintain the combustion reactions. Increasing oil content and air injection rate can increase the cumulative oil and gas production, but there are optimal values above which the increase rate slows down. The energy conversion efficiency of in situ combustion is 49.5, and it is much higher than the energy conversion efficiency in other in situ upgrading methods for oil shale.

Hydraulic fracturing through a multiborehole cluster is a crucial technology for the enhancement of shale gas reservoir production. However, the impact of borehole interference and in situ stress on hydraulic fracturing is still unclear. This study developed a multiscale hydraulic coupling model by improving the algorithm of the traditional pipe domain model within discrete element method and the initiation and propagation of hydraulic fractures under in situ stress and three multi-borehole clusters were numerically studied. Numerical results indicate that fracture development is initially governed by bedding planes, followed by the maximum principal stress. Tensile fractures account for over 80% of the observed fractures. As the lateral pressure coefficient decreases from 1, the proportion of tensile fractures decreases, while shear fractures become more prominent. The circumferential stress primarily influences fracture propagation, while radial stress plays a key role in governing fracture connectivity. During hydraulic fracturing of multiborehole clusters, the vicinity of the boreholes is prone to stability loss, and the stress shadow significantly affects the generation of fracture network. These results can deepen our understanding on the fracture network development and provide a guidance for the application of hydraulic fracturing technology.

Abstract

The demand for the development of high-capacity, safe, and long-life secondary batteries and the interest in all-solid-state batteries are increasing. The cycle performance of solid-state batteries is limited by interfacial phenomena at the electrolyte–anode interface hindering the ion diffusions. A multifunctional aluminum oxide (specifically, ${\mathrm{Al}}_2{\mathrm{O}}_3$) coating was created for application on silicon-based anodes in all-solid-state lithium-ion batteries. In an all-solid-state lithium-ion battery, the electrochemical properties of ${\mathrm{Al}}_2{\mathrm{O}}_3$ coating were enhanced. The coating was applied to provide stable artificial solid electrolyte interphase (SEI) layers on the silicon-based anodes. ${\mathrm{Al}}_2{\mathrm{O}}_3$ layers not only promote the diffusion of ${\mathrm{Li}}^{+}$ through the Li–Al–O, but their intrinsically low electronic conductivity also limits the transmission of electrons at the contact between the anode and the electrolyte. A Si alloy–polyacrylonitrile anode was prepared using ${\mathrm{Al}}_2{\mathrm{O}}_3$ coating as an artificial SEI layer by radio-frequency (RF) plasma. Radio-frequency sputtering was used to create a simple and economical ${\mathrm{Al}}_2{\mathrm{O}}_3$ coating. The cycle properties of silicon-based anodes were enhanced by the addition of the thin amorphous aluminum oxide layer (i.e., ${\mathrm{Al}}_2{\mathrm{O}}_3$ coating). After 100 charge–discharge cycles, the half-cell with the ${\mathrm{Al}}_2{\mathrm{O}}_3$ layer delivered a discharge capacity of $502.08\mathrm{mAh}{\mathrm{g}}^{-1}$ and a capacity retention ratio of 58.86%. After 100 cycles, the sample without the ${\mathrm{Al}}_2{\mathrm{O}}_3$ layer had a discharge capacity of $278.48\mathrm{mAh}{\mathrm{g}}^{-1}$ and capacity retention of 34.34%. Cells with an ${\mathrm{Al}}_2{\mathrm{O}}_3$-coated anode retained high capacity after 100 cycles. Thus, the ${\mathrm{Al}}_2{\mathrm{O}}_3$-coated Si-based anodes were cycled successfully in all-solid-state half-cells to produce functional high-performance lithium-ion batteries.

Practical Applications

In this study, we employed the vacuum deposition method, radio-frequency sputtering, to deposit very thin layer of aluminum oxide on the surface of fully fabricated anodes for improved cycling properties of all solid-state battery. This layer of aluminum oxide was confirmed using advanced elemental analysis techniques. The aluminum oxide layer with 1-min coating had much-improved cycling characteristics compared with those of the sample with no coatings. Previous studies have used theoretical calculations to report that an aluminum oxide coating layer improves the stability characteristics for sulfide-based solid electrolytes. In this paper, the actual stability improvement of the sulfide-based solid electrolyte was demonstrated in terms of much improved cycling characteristics throughout the cycling test. The appropriate amount of aluminum oxide coating decreases the decomposition of solid electrolyte and also decreases the consumption of Li ions during lithiation and delithiation. This surface modification technique can be utilized to improve the cycling stability of solid-state batteries, which is one of the critical factors for the early adoption of solid-state batteries for electric vehicle applications.

Coal seam water injection is a widely employed strategy to mitigate dust in coal mines, and the effectiveness of water injection is intricately linked to the internal pore and fracture structure of the coal. During the process of coal mining, the stress induced by mining activities has a significant impact on the pore and fracture structure of the coal mass surrounding the borehole, consequently altering its seepage characteristics. In order to investigate the seepage evolution patterns of coal seams, this study was based on in situ micro-computed tomography (CT) imaging tests to extract the interconnected fracture models of a coal sample under various axial force loading conditions. Subsequently, a numerical simulation was conducted to simulate water injection seepage and analyze the permeability evolution of coal. According to the obtained results, when the axial force was loaded from 431 N to 732 N, the interconnected fractures inside the coal increased, and the seepage velocity and mass flow rate increased slightly. When the axial force was loaded to 1,100 N, the interconnected fractures experienced a further increase in number, leading to the formation of a complicated interconnected fracture network. Therefore, the resistance of water in seepage increased, resulting in a slight decrease in seepage velocity, but a significant increase in mass flow rate. When the axial force reached 492 N after the peak load, a stable interconnected fracture network was formed in the coal, the fracture development became slow, and the seepage rate as well as the mass flow rate reached a relatively stable state. Under the influence of axial force loading, the fracture structure within coal exhibits significant development, leading to a notable enhancement in its seepage characteristics. The research findings presented in this paper hold significant practical implications for the utilization of mining-induced stress in guiding the design of parameters for coal seam water injection and its subsequent field application.

Gravitational instability in porous media is observed in numerous natural systems in which reaction at the penetrating chemical front is a common occurrence. Most often, this reaction kinetics is difficult to capture and explain adequately using the classical linear reaction rate profiles.The nonlinearity of the reaction rate addresses the general reaction framework that may be encountered in natural settings and has substantial ramifications for the overall gravitational instability dynamics at long times. However, the way in which a nonlinear reaction affects the dissolution in combination with porous dispersion has remained largely elusive. This study used a two-dimensional (2D) numerical framework built in OpenFOAM to capture the coupled effect of nonlinear reaction kinetics and porous dispersion on the ensuing gravitational instability across a miscible fluid pair. This study quantitatively explored the instability onset times, total dissolution of heavier fluid, and convective dynamics as a function of the nonlinearity in the chemical kinetics in dispersive porous media. We hereby report intriguing and nonintuitive effects on induced gravitational instability in the presence of nonlinear chemical reactions. The results show a decrease in the nonlinear onset time and increase in overall dissolution with stronger reaction rate. The onset time and overall dissolution varied with the nonlinearity of the reaction kinetics. This study focused on the enhancement of effective dissolution employing the inherently occurring chemical reactions in natural systems, and is a model tool to understand various geological reaction-transport and sequestration phenomena.