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In the present work, the corrosion behavior of ultra-high strength steel (UHSS)-high strength steel (HSS) welded joint is investigated. In situ scanning Kelvin probe (SKP) and scanning vibrating electrode technique (SVET) are used to study the galvanic corrosion of the dissimilar welded joint in natural seawater medium. The UHSS zone is revealed to be the most cathodic region. Meanwhile, the HSS has a high anodic activity. The corroded surface shows that the calcareous deposit is observed in UHSS zone, and the rust layer is formed in HSS and weld metal (WM) zones. When the corrosion product layer is removed, the UHSS zone is revealed to suffer from the pitting corrosion, and the HSS and WM zones exhibit the uniform corrosion. [ABSTRACT FROM AUTHOR]

It is important to investigate interfacial effects on liquid transport characteristics through nanopores with strong wettability due to potential applications in several fields. The structural and transport properties of wetted liquid argon through nanochannels were investigated via molecular dynamics (MD) simulations. A mathematical model for liquid flow in nanoporous media was established based on the constant negative slip length by combining MD simulations with fractal theory for complex media. The results show that the strong liquid–solid attraction allows the liquid to be adsorbed onto the solid walls. In addition, compared with the bulk diffusion coefficient in the center of the nanochannel, the coefficient parallel to the interface near the solid walls is largely reduced, indicating the liquid molecules are strongly bound to the solid walls. Furthermore, negative slip can exist in the vicinity of solid walls with strong wettabilities. The variations in negative slip length with the external driving force can be characterized by two regimes. In steady negative slip regime, the negative slip length remains constant. As the driving force continues to increase, the transition negative slip regime exists, where the negative slip length decreases linearly with the driving force until the slip length becomes zero. The presence of a negative slip length reduces the liquid flow rate compared with no slip or a positive slip length due to the reduced effective cross section for fluid transport. Moreover, the increased fractal dimensions about the capillary radius result in an enhanced liquid flow rate, while that about the tortuosity reduces the liquid flow rate. [ABSTRACT FROM AUTHOR]

It is of great importance to determine the risk grades of the leakage and non-leakage cases of concentrated saltwater from an underground reservoir for the safe operation of reservoirs and environmental protection. In this paper, the model of risk evaluation for environmental pollution of an underground reservoir stored with concentrated saltwater is established. Moreover, the effects of different influencing factors on the risk grades are investigated, along with an uncertainty analysis. In addition, the risk grade of Lingxin Mining Area is calculated, which can contribute to the prevention and control of pollution in the future for that area. The results show that the water quality complexity of mine water is the most significant indicator for risk grade determination. The certainty of weak-risk grade for environmental pollution caused by an underground reservoir when there is no leakage is more than 60% in the Lingxin Mining Area, and the risk grade becomes a strong-risk grade rapidly after concentrated saltwater leakage is considered. This research can provide a theoretical basis for risk control and management of underground reservoirs storing concentrated saltwater. [ABSTRACT FROM AUTHOR]

The past two decades have borne remarkable progress in our understanding of flow mechanisms and numerical simulation approaches of shale gas reservoir, with much larger number of publications in recent 5 years compared to that before year 2012. In this paper, a review is constructed with three parts: flow mechanism, reservoir models and numerical approaches. In mechanism, it is found that gas adsorption process can be concluded into different isotherm models for various reservoir basins. Multi-component adsorption mechanisms are taken into account in recent years. Flow mechanism and equations vary with different Knudsen numbers, which could be figured out in two ways: molecular dynamics (MD) and lattice Boltzmann method (LBM). MD has been successfully applied in the study of adsorption, diffusion, displacement and other mechanisms. LBM has been introduced in the study of slippage, Knudsen diffusion and apparent permeability correction. The apparent permeability corrections are introduced to improve classic Darcy's model in matrix with low velocities and fractures with high velocities. At reservoir-scale simulation, gas flow models are presented with multiple porosity classified into organic matrix with nanopores, organic matrix with micropores, inorganic matrix and natural fractures. A popular trend is to incorporate geomechanism with flow model in order to better understand the shale gas production. Finally, to solve the new models based on enhanced flow mechanisms, improved macroscopic numerical approaches, including the finite difference method and finite element method, are commonly used in this area. Other approaches like finite volume method and fast matching method are also developed in recent years. [ABSTRACT FROM AUTHOR]

In this paper, a microscopic visualization experiment is conducted to explore the heterogeneous flow pattern of micro polymer particles in micron pore. A capillary bundle network model for micro polymer particles in porous media is established. The migration and retention mechanism of polymer particles can be clearly observed in the experiment and simulated with this numerical model. The result demonstrates that the block of large particles is one of the main factors by which micro polymer particles increase the flow resistance. The simulation results are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Beijing-Tianjin-Hebei (BTH) region in China is affected seriously by the hazy weather that has a large impact on human health. PM is one of the most important reasons for hazy weather. Understanding the PM emission characteristics from different types of heavy-duty trucks (HDTs) is valuable in policies and regulations to improve urban air quality and mitigate vehicle emission in China. The investigation and analysis on HDT population and PM emission in BTH region are carried out. The results show that the population and PM emission of HDTs in BTH has risen for the last four consecutive years, from 404 thousand and 1795 tons in 2012 to 551 thousand and 2303 tons in 2015. The PM emission from HDTs in Hebei is about 10 times more than that of Beijing and 9 times more than that of Tianjin. The proportion of natural gas HDTs is about 5%; however, its PM emission only accounts for 0.94% in 2015, which indicates the utilization of HDTs powered by natural gas facilitate PM mitigation more than diesel in BTH. The tractor and pickup trucks are the main source of PM emission from different types of HDT, while special and dump trucks are relatively clean. This study has provided insights for management method and policy-making of vehicle in terms of environmental demand. [ABSTRACT FROM AUTHOR]

Introduction: This study focused on using analytical and numerical models to develop and manage groundwater resources, and predict the effects of management measurements in the groundwater system. Movement of contaminants can be studied based on groundwater flow characteristics. This study can be used for prediction of ion concentration and evaluation of groundwater pollution as the theoretical basis. Case description: The Yimin open-pit mine is located in the northern part of the Inner Mongolia Autonomous Region of China. High concentrations of iron and manganese are observed in Yimin open-pit mine because of exploitation and pumping that have increased the concentration of the ions in groundwater. In this study, iron was considered as an index of contamination, and the solute model was calibrated using concentration observations from 14 wells in 2014. Discussion and evaluation: The groundwater flow model and analytical solutions were used in this study to forecast pollution concentration and variation trend after calibration. With continuous pumping, contaminants will migrate, and become enriched, towards the wellhead in the flow direction. The concentration of the contaminants and the range of pollution increase with the flow rate increased. Conclusions: The suitable flow rate of single well should be <380 m/day at Yimin open-pit for the standard value of pollution concentration. [ABSTRACT FROM AUTHOR]

In this paper, a simple but accurate method (generalized large well method) is presented to assess groundwater level trends during mine exploitation. This method includes a mathematical model of confined-unconfined well flow and a corresponding analytical solution. Based on the method, a case study was analyzed with data from the Yimin open-pit mine. As a result, the radius of groundwater level rose, along with the increase of the exploitation intensity. Moreover, a suitable value of pumping flow could be beneficial to understanding potential groundwater contamination concerns. Additionally, it has also been predicted that the groundwater level of the Yimin open-pit mine will change within the next 3 years. The Yimin open-pit mine case study demonstrates the validity of the analytical method explained herein. The presented methodology provides a theoretical foundation for assessment of groundwater changing trends in other open-pit mines with similar hydrogeological conditions. [ABSTRACT FROM AUTHOR]

Coalbed methane plays a significant role for the sustainable utilizing of resources and ecological environment. Production capacity forecasting of coalbed methane wells can effectively guide the optimization of development schemes directly affecting the economic benefits. To overcome the inefficiency of traditional theory-based numerical simulators and their weak adaptability to observational data, we explore a potential and efficient alternative for modeling of production capacity in a data-driven approach. This study makes full use of dynamic production data and geological static data from 530 CBM wells. We develop a production capacity prediction model utilizing the extreme gradient boosting algorithm and incorporated bayesian optimization to implement an automated search for hyperparameters. The results demonstrate that the prediction model developed by extreme gradient boosting has a more powerful prediction performance with an R2 close to 0.9 compared to other machine learning or even deep learning. Moreover, the coupled framework of extreme gradient boosting and bayesian optimization can notably upgrade the prediction power of the production capacity model by about 8%. The analysis of influencing factors also illustrates that dynamic production data during the first three years of development can well characterize the coalbed methane adsorption–desorption-seepage features, which contribute to the construction of the production capacity model. [ABSTRACT FROM AUTHOR]