Greenhouse Gases: Science and Technology最新文献

CO₂ replacement method is an auspicious method for the CH₄ extraction from gas hydrate and the CO₂ geological storage into sediments. The replacement of CO₂CH₄ hydrate in porous medium system is jointly affected by many factors such as heat transfer, mass transfer, and reaction. It is of great significance to deeply understand the mechanism and dynamics of different factors influencing the replacement characteristics of CO₂CH₄ hydrate in porous media. In this study, the molecular dynamics simulation method was employed to study the replacement characteristics and kinetic process of CO₂CH₄ hydrate in porous medium system with varying conditions expecting to offer significant theoretical direction and a point of reference for the CO₂ replacement method of natural gas hydrate extraction in permafrost regions in reality. The quantitative influence and internal mechanism of different factors on the replacement process of CO₂CH₄ hydrate were revealed. The results show that, in the porous medium system, when the temperature was ranged of 265–270 K and the pressure was ranged of 10–20 MPa, the replacement effect of CO₂CH₄ hydrate is the best under the initial concentration of CO₂ of 100%. It was further indicated that the replacement effect is appropriate when the initial concentration of CO₂ was ranged of 40%–60% under the case of 265 K and 10 MPa. Moreover, the result also indicated that the effects of some certain factors, including temperature, pressure, and initial concentration of CO₂ on the replacement process of CO₂CH₄ hydrate, exist slightly different. Owing to the adsorption effect of porous media on CO₂ molecules, it reduced the replacement efficiency between CO₂CH₄ hydrate. Additionally, the initial concentration of CO₂ imposed a more significant influence on the replacement of CO₂CH₄ hydrate in porous medium system considering the adsorption effect of porous. It does not mean that the higher the initial concentration of CO₂, the better the replacement effect of hydrate. The diffusion capacity of CO₂ depends on the concentration of H₂O molecules and the adsorption effect of porous media.

CO₂, being a major greenhouse gas, is regarded as an important contributor to global warming and environmental problems. CO₂ capture and separation are an efficient approach for reducing CO₂ emissions in the atmosphere. A hydrate method of CO₂ capture and separation provides a feasible solution to the emission reduction of CO₂ in the atmosphere. However, the rapid formation of hydrate is crucial for CO₂ capture and separation using the hydrate technique. As a consequence, this paper comprehensively reviewed the rapid formation characteristics and the kinetic law of CO₂ hydrate, as well as deeply analyzed the influences of temperature and pressure conditions, gas–liquid ratios, additives, hydration reaction system, hydration reaction process, and other factors on its formation process. On this basis, the quantitative impact and regulatory mechanisms of different factors on the nucleation and growth process of CO₂ hydrate were comprehensively analyzed. The influence mechanisms and kinetic laws of temperature, pressure, gas–liquid ratio selection, additive concentration, and type of reaction system on CO₂ hydrate rapid formation were detailed. The regulatory and enhancement mechanisms of CO₂ hydrate rapid formation under multiple factors were elucidated. The application of CO₂ capture by the hydrate method and its challenges are summarized. In the end, the key problems and future directions of rapid CO₂ capture and separation using the hydrate method were pointed out. The synergistic mechanism of rapid CO₂ hydrate formation and the enhancement through multiple factors still need to be further investigated. Developing new reactor structures and optimizing the hydration reaction process are important in promoting the rapid formation of CO₂ hydrate.

Investigating the migration of carbon dioxide (CO₂) fluids is essential for the effective monitoring in the geological sequestration of CO₂. Traditional numerical simulation methods are often time-consuming and computationally expensive. Recently, deep learning methods, particularly convolutional neural networks (CNNs), have gained traction for predicting CO₂ plume migration. However, these approaches typically require extensive training datasets and tend to emphasize local information. To overcome these limitations, we introduce a visual attention model along with a novel neural network based on the Swin Transformer architecture to forecast CO₂ plume migration in heterogeneous geological formations. A significant challenge in conventional machine vision is the translational invariance of input images, which can hinder performance. To address this issue, we integrate relevant physical prior knowledge into our model. Compared with U-net and Transformer, the model exhibits highest predictive performance, with an R² score of 0.9741 and the test set root mean squared error (RMSE) reaching 0.0245. These results indicate that this approach enables the network to effectively extract both local and global features, maximizing the use of limited datasets and enhancing the understanding of CO₂ migration patterns. Additionally, the model demonstrates strong capabilities for global information learning and generalization. These advantages, therefore, facilitate the extensive application of the visual attention model in predicting CO₂ migration.

Gas breakthrough pressure is a key parameter affecting gas production and evaluation of tight reservoir sealing capabilities. This study aims to explore the impact of different injection methods on CH₄ breakthrough pressure in unsaturated rocks. COMSOL Multiphysics was used to simulate the CH₄ breakthrough process, and comparative analysis was conducted using step-by-step and continuous injection methods. The results show that the step-by-step method has higher measurement accuracy under low CH₄ breakthrough pressure and is suitable for scenarios that require precise evaluation, whereas the continuous injection method is more efficient under high CH₄ breakthrough pressure and is suitable for rapid evaluation needs. According to outcomes of simulation, this research suggested a numerical optimization framework aimed at forecasting the breakthrough pressure of CH₄ and verified the accuracy and applicability of the model through linear fitting of experimental data and predicted values. In addition, the study also conducted a sensitivity analysis on the pore distribution index (m) and injection flow rate (u_in) in the van Genuchten model. The results show that u_in has a small impact on breakthrough pressure, whereas m has a considerable effect on breakthrough pressure. An increase in m leads to an increase in breakthrough pressure, thereby enhancing the sealing performance of rock core. This study reveals the applicability difference between the step-by-step method and the continuous injection method in predicting CH₄ breakthrough pressure and proposes an effective prediction method based on numerical simulation, which provides valuable insights for selecting gas injection methods and predicting breakthrough pressure in rocks. © 2025 Society of Chemical Industry and John Wiley & Sons, Ltd.

The use of fossil fuels to fulfill energy demand is responsible for CO₂ emissions, resulting in global warming and climate change. Despite the expansion in renewable energy sources, energy combustion and industrial processes caused a 0.9% increase (321 Mt) in global CO₂ emissions to a record high of 36.8 Gt in 2022. Carbon capture and sequestration (CCS) technology can allow the use of fossil fuel without damaging the environment by storing CO₂ underground, paving the way for a sustainable, low-carbon future. Without fracturing, both homogeneous and low-permeability aquifers can safely accommodate injected CO₂. This study investigates the effect of low-permeability layers composed of sandstone and shale layers on the capacity and performance of CO₂ storage in open saline aquifers. The CO₂ migration, dispersion, and reservoir pressure variations have been numerically investigated in a computational domain representing the Utsira Formation in Sleipner CCS project. In a homogeneous aquifer, rapid vertical migration results in 65% of the injected CO₂ accumulating at the top layer after 30 years. However, the presence of four low-permeability layers reduces this accumulation to 58% over the same period, demonstrating enhanced trapping efficiency. Long-term simulations indicate that CO₂ accumulation at the top surface increases to 75% of the total injected volume over 80 years. CO₂ dissipates and migrates over time, resulting in a decrease in surface pressure. Pressure analyses reveal that the peak injection-induced pressure remains within the fracture pressure limit (20–25 MPa), ensuring safe storage. After 30 years of injection, pressure at the top surface drops by 0.27 MPa (2.72%) within 2 years post-injection and continues to decrease gradually. This investigation contributes to a better understanding of the dynamics of CO₂ storage in open saline aquifers, thereby facilitating the development of effective CO₂ sequestration strategies. © 2025 Society of Chemical Industry and John Wiley & Sons, Ltd.

The performance of bimetallic catalysts is closely related to their surface structure, and the surface reconstruction process can affect the distribution of active sites, electronic structure, and reactant adsorption behavior. Traditional research has mostly focused on optimizing synthesis processes, such as controlling the size and distribution of metal particles, whereas there is relatively little research on the effect of pretreatment conditions on the dynamic structure of catalysts. In this study, a 10Ni─1Cu catalyst was synthesized using the deposition–precipitation method, and the effects of different pretreatment conditions on its performance were investigated. The catalyst was first pretreated at 500°C in a 60%H₂/40%N₂ atmosphere, followed by reduction under different pretreatment atmospheres (10%H₂/90%N₂ or 15%CO₂/60%H₂/25%N₂) at the same temperature. At 400°C and a space velocity of 30 L h⁻¹ g⁻¹, the methane production rate of the catalyst treated in the reaction atmosphere significantly increased from 12.4 to 15.8 µmol g⁻¹ s⁻¹ compared to the catalyst treated with hydrogen alone. Characterization techniques, such as TEM, x-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS), were employed to study the structural properties of the catalysts, focusing on the surface properties after reduction and the surface species during the reaction. This study demonstrates that catalysts pretreated in the reaction atmosphere enhance methane production rates by regulating the surface structure and forming Ni─Cu alloy structures with a lower Ni/Cu ratio, thereby optimizing the selectivity of hydrogenation products.

This work represents an extensive molecular dynamics (MDs) simulation study with the microstructural insight at the interface to simultaneously predict the phase equilibria, transport, and interfacial properties of the CO₂–H₂S–brine system within the range of temperatures 323.15–393.15 K, pressures up to 30 MPa, H₂S contents of 0–70 mol%, and salt molalities of 1–4 mol/kg, aiming to address the insufficiency of data under typical conditions of acid gas sequestration. The validation results demonstrate that the average absolute deviations (AAD%) for the predicted solubility of CO₂ and H₂S in water and in 2 mol/kg NaCl solution were found to be 5.45%, 6.34%, 5.78%, and 5.41%, respectively. Moreover, the AAD% for interfacial tension (IFT) and density were 6.74% and 3.70%, respectively, verifying the validity and performance of the applied force field parameters and computational methods. The simulation results indicated that H₂S solubility in brine is more sensitive to changes in the acid gas composition and temperature compared to CO₂ solubility. The presence of H₂S remarkably reduces the CO₂–H₂S–brine IFT, with the reduction degree depending on the H₂S content. Increasing the H₂S mole fraction in acid gas mixtures delays convective mixing by reducing the brine density. At about 64 mol% H₂S, the aqueous solution's density equals that of fresh brine, which is the highest H₂S content that can maintain the benefit of convective mixing in the dissolution trapping. The maximum acid gas column height that can be safely stored is most significant at lower temperature and H₂S content. On the basis of the results, pressure, temperature, and salt molality have a higher influence on the viscosity than density in the studied ranges. The new data generated by the current study can be utilized to develop predictive models of acid gas long-term behavior, which will reduce the uncertainty of real storage schemes.

This study aims to accurately predict the risk of coal and gas outbursts in coal seams located near small faults. Models of small-scale normal faults in the Changping mine field were constructed using the FLAC3D software, with fault dip angles of 65° and 70°, and drops of 1, 3, 5, 8, and 10 m. The objective was to analyze the effects of fault drop and dip angle on stress distribution near the faults and to predict the related outburst risks. The results indicate that in the hanging wall of the fault, the peak stress correlates with the fault drop through a linear function, whereas the range of influence is described by a quadratic function. As the fault drop increases, the impact range and stress peak also increase. The position of the stress peak gradually shifts away from the section, whereas the stress concentration area widens. Furthermore, the protruding danger zone expands and similarly moves farther from the section. When the fault drop is constant, the impact range of the 65° dip fault is smaller; however, the stress peak and the stress concentration zone in the nearby coal seam are larger and closer to the fault surface. Additionally, the highlighted danger zone is also larger and nearer to the fault surface. On the basis of the measured fundamental parameters of coal seam gas in the region, within a distance of 6 m from the fault surface (Zone I), there is a significant influence from the fault, resulting in a higher risk of outburst in this area. In the range of 6–15 m from the fault surface (Zone II), the gas content continues to increase, leading to an overall heightened risk of outburst.