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A large number of laboratory investigations related to the permeability have been conducted on the sliding zones. Yet little attention has been paid to the particular sliding zones of the slide-prone Badong Formation. Here, we experimentally investigate the permeability nature and the mechanism of seepage in the viscous sliding zone of the Huangtupo Landslide. Saturated seepage tests have been performed first with consideration of six dry densities and thirteen hydraulic gradients, in conjunction with the mercury intrusion porosimetry test and scanning electron microscopy test for the microstructure analysis after seepage. The results show that seepage in the sliding zone soil does not follow Darcy's Law, since there is a threshold hydraulic gradient (i0) below which no flow is observed and a critical hydraulic gradient (icr) over which the hydraulic conductivity (K) tends to be stable. The percentage of bound water could be responsible for the occurrence of i0 and icr. Furthermore, pore size distributions (PSD) less than 0.6 µm and between 10 and 90 µm exhibit positive and negative correlations with the i0, respectively, indicating that the i0 is related to the PSD. The mechanism accounting for this result is that pore water pressure forces fine clay particles into the surrounding large pores and converts arranged particles to discretely distributed ones, thereby weakening the connectivity of pores. The seepages in the sliding zones behave differently from that in the sliding mass and sliding bed in response to the permeability. [ABSTRACT FROM AUTHOR]

In the process of coalbed methane development, drilling fluid and fracturing fluid cannot achieve absolute compatibility with formation. The incompatibility between the working fluid and reservoir will lead to the intrusion of working fluid into the reservoir and cause reservoir pollution. This is a very common phenomenon. There is a large amount of pulverized coal in the coal seam, and the intrusion of working liquid will be combined with the pulverized coal to form cement to block the seepage space in the reservoir. Since pressure relief and fracturing fluid backflow will be performed at the first time after fracturing, the intrusion range of the working fluid is small, generally reaching 10 m to 50 m. Compared with a conventional gas reservoir or shale gas reservoir, the working fluid loss during CBM development will seriously affect the subsequent production project and even make the gas well lose production capacity. On the other hand, in order to avoid this phenomenon, measures such as acidification or volumetric fracturing are sometimes used to improve the seepage environment near the well and near the fracture. The purpose of this study is to quantitatively evaluate the impacts of working fluid filtration and reservoir reconstruction on production. In this study, a single well productivity evaluation model and sensitivity analysis method considering drilling fluid filtration loss, fracturing fluid filtration loss, reservoir reconstruction and other processes is proposed. The formation mechanism of fluid loss during drilling and fracturing is described, and the productivity evaluation model considering fluid loss is combined with the Langmuir isothermal adsorption equation, steady-state diffusion law, Darcy's seepage law and Duhamel convolution formation. Combined with the distribution of actual gas reservoir flow characteristics, the sensitivity of single well productivity to gas reservoir porosity, gas reservoir permeability, coal seam adsorption coefficient, working fluid filtration loss and reservoir reconstruction measures are analyzed. Through the analysis and fitting of the actual production data on site, the relationship curve can better fit the field production data, and the evaluation results are in line with the drilling and fracturing conditions at that time and the subsequent production conditions, with small errors. The obtained method is suitable for predicting the productivity of fractured vertical wells in different working conditions and provides a basis for the development and productivity prediction of CBM reservoirs in China and in international cooperation. [ABSTRACT FROM AUTHOR]

The measurement of groundwater exchange between neighboring regions is a critical topic in water resource management and can usually be achieved through a combination of field investigations and the use of groundwater flow models. In this study, we employed the water balance and Darcy's law methods, utilizing downscaled Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) data to assess groundwater exchange patterns in the Beijing-Tianjin-Hebei (BTH) region of China. Additionally, we determined the contributions of human activities and climate factors to the observed variations via residual analysis. The results revealed a consistent decrease in groundwater storage in the study area since 2008, especially in the spring and summer months. The groundwater exchange rates calculated by 1° and 0.05° groundwater storage anomalies (GWSAs) were basically consistent, and the downscaled GWSAs could better reflect the small-scale groundwater exchange characteristics. The groundwater exchange rate showed a decreasing trend from the Piedmont plain to the coastal areas. A notable trend of declining groundwater exchange between the Taihang Mountains and Piedmont plains was observed, and the downward trend gradually intensified from north to south between 2003 and 2007. After 2008, there was an increasing trend, and coastal areas exhibited the smallest amount of groundwater exchange. Human activities emerged as the predominant factor accounting for more than 90.9% of the overall reduction in groundwater storage, while climate change imposed a minimal influence on groundwater storage variations. The insights obtained in this study hold significant implications for groundwater resource planning and management in the region. [ABSTRACT FROM AUTHOR]

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Heilongjiang Province, the largest commercial grain base in China, experiences significant challenges due to the environmental effects on its soil. The freezing and thawing cycle in this region leads to the transport of water and heat, as well as the exchange and transfer of energy. Consequently, this exacerbates the flooding disaster in spring and severely hampers farming activities such as plowing and sowing. To gain a better understanding of the freezing and thawing mechanisms of farmland soil in cold regions and prevent spring flooding disasters, this study focuses on Heilongjiang Province as a representative area in northeast China. The research specifically investigates the frozen and thawed soil of farmland, using a large-scale low-temperature laboratory to simulate both artificial and natural climate conditions in the cold zone. By employing the similarity principle of geotechnical model testing, the study aims to efficiently simulate the engineering prototypes and replicate the process of large-span and long-time low temperatures. The investigation primarily focuses on the evolution laws of key parameters, such as the temperature field and moisture field of farmland soil during the freeze–thaw cycle. The findings demonstrate that the cooling process of soil can be categorized into three stages: rapid cooling, slow cooling, and freezing stabilization. As the soil depth increases, the variability of the soil temperature gradually diminishes. During the melting stage, the soil's water content exhibits a gradual increase as the temperature rises. The range of water content variation during thawing at depths of 30 cm, 40 cm, 50 cm, and 80 cm is 0.12% to 0.52%, 0.47% to 1.08%, 0.46% to 1.96%, and 0.8% to 3.23%, respectively. To analyze the hydrothermal coupling process of farmland soil during the freeze–thaw cycle, a theoretical model of hydrothermal coupling was developed based on principles of mass conservation, energy conservation, Darcy's law of unsaturated soil water flow, and heat conduction theory. Mathematical transformations were applied after defining the relative degree of saturation and solid–liquid ratio as field functions with respect to the relative degree of saturation and temperature. The simulated temperature and moisture fields align well with the measured data, indicating that the water–heat coupling model established in this study holds significant theoretical and practical value for accurately predicting soil temperature and moisture content during the spring sowing period, as well as for efficiently and effectively utilizing frozen soil resources in cold regions. [ABSTRACT FROM AUTHOR]

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China is a country with the most widely distributed karst, and the karst is extensively developed in its southwesten part where 2,836 underground rivers are distributed with about 1,847.8 x 108 m³⋅a-1 of karst groundwater resources and a total discharge of 479.7 x 8 m³⋅a-1 in the dry season. These underground rivers become the main water source for people's life as well as the development of industry and agriculture in Southwest China. However, water shortage has often occurred in recent years, due to the unreasonable development and utilization of karst water resources. How to make scientific, reasonable and effective use of karst water resources has become a difficult problem in tackling water resource crisis. In this paper, we have studied the hydrological process and numerical simulation of groundwater in karst areas from the perspective of groundwater science, which is of great significance to the accurate evaluation, and rational development and utilzation of karst water resources. In this study, we take Dajing basin, a typical karst peak-cluster depression area in southern Guizhou Province, as the study area. Water-bearing media in karst areas often include karst pipelines with high permeability and dissolved gaps with low permeability. The flow mechanism of groundwater in these two media is quite different. The groundwater in the gap mainly accords with Darcy's law and the laminar flow mechanism, while the groundwater in the karst pipeline is mostly in the turbulent state due to the large flow rate. In the actual situation, the two media are independent of each other, but there is an interrelated process of hydraulic exchange on the boundary. Based on this, we adopt MODFLOW-CFP coupling model to carry out a numerical simulation of Dajing basin. MODFLOW-CFP is a dual-system coupling model based on dual structure theory. MODFLOW-CFP model contains three groundwater flow simulation methods. In this study, CFPM1, the most basic model, is adopted. In this pattern, the traditional groundwater flowing model is coupled with a specific pipeline model. The main purpose is to depict caves, cracks in interstitial space and basaltic aquifer pipes in karst aquifers, where groundwater can be fully or partially filled and flow patterns can be laminar or turbulent. Therefore, a complete simulation of the hydrological process of karst groundwater may help us to grasp the law of groundwater movement in Dajing basin, accurately evaluate karst water resources, and thus promote the rational development and utilization of the resources. The process of using MODFLOW-CFP to establish a mathematical model of groundwater in Dajing basin includes the establishment of porous media model in MODFLOW and pipeline model in CFP. Subsequently, the two models are combined together to identify the model and analyze the water balance, based on the coupling model. Finally, the water resources are evaluated and the mechanism of groundwater migration is studied. In this study, it is found that Dajing basin is a groundwater system with complete recharge, runoff and drainage conditions, and the North-South and the Northeast-Southwest trending structures control the distribution of regional karst aquifers and the development of karst. According to the buried conditions of groundwater and the practical significance of water supply, the main source of recharge in this area is atmospheric rainfall, and the main discharge is the outflow from the southern Dajing basin. Meanwhile, the simulation results show that the exchange capacity between pipes and porous media is 6,719.1 m³⋅a-1, mainly in the upper and middle reaches of Dajing basin. The total recharge water in the study area is 10,977.3 x 104 m³⋅a-1, and the recharge module is 133.495 m³⋅km-2⋅a-1. The rainfall inflow and infiltration accounts for 81.35% of the total recharge, and the total discharge is 10,813.47 x 104 m³⋅a-1, mainly from the outlet of the underground river. Based on the research findings, the migration mechanism of groundwater in Dajing basin is clarified, and new development and utilization of water resources are put forward to address the shortage of local water resources. [ABSTRACT FROM AUTHOR]

Ionic rare earth ore is a type of featured rare earth ore in China. Its mining process suffers from a long leaching cycle and considerable consumption of leaching agents. Improving mining efficiency requires a sound physical understanding of the leaching process. In this study, the CFD-based numerical model is used to analyze the physical process of leaching through porous media formed by particles. The simulation results indicate that a lower packing porosity and smaller particles packed granular porous medium result in much larger energy dissipation during seepage, and the energy dissipation increases with seepage velocity. It is found that when the seepage velocity increases to a certain high value, the energy dissipation exceeds the value predicted by Darcy's law, which is mainly caused by liquid turbulence. Additionally, the effect of particle shape is examined. The results show that the granular medium composed of prolate particles causes larger energy dissipation than oblate particles, and spherical particles play the least role. This phenomenon may result from the particle shape affecting the area of the frontal contact surface between particles and liquid. The results provide new insights into the fundamental understanding of percolation and seepage behaviors in the ion-adsorption-type rare earth ore leaching process. [ABSTRACT FROM AUTHOR]

Straw mulching has been one of the important measures of conservation tillage, particularly for the soil and water conservation. This study aims to systematically investigate the effect of straw coverage on the hydrodynamic characteristics of overland flow. A series of the indoor fixed-bed simulation experiments were carried in the Soil and Water Conservation Engineering Laboratory in Northwest A&F University, located in the southern Loess Plateau, Shaanxi Province, China (34°14′N-34°20′N, 107°59′E-108°08′E). The experimental conditions of five flow rates (3.0, 4.5, 6.0, 7.5, and 9.0 L/min), and four slope gradients (3°, 5°, 10°, and 15°). An analysis was made to determine the variations in the hydrodynamic parameters of bare slope and different straw cover (0, 1.5, 2.5, 3.5, and 4.5 t/hm²). Hydrodynamic parameters included the flow velocity, Reynolds number, Froude number, and Darcy-Weisbach resistance coefficient. The systematic investigation was also implemented to clarify the effects of straw mulch on the flow pattern, flow regime, and resistance characteristics of overland flow. The results showed that: 1) Straw mulching affects the flow pattern and flow regime of overland flow. Specifically, the flow pattern of overland flow was the rapid flow without straw coverage under different flow rate and slope. But, the tranquil flow was found under straw mulching. One the flow rate was ≤7.5 L/min, the flow pattern was the laminar flow. By contrast, when the flow rate was >7.5 L/min, the flow pattern was the transition flow. 2) The flow velocity showed a decreasing trend as a whole under the same flow rate and slope, with the increase of straw coverage. The flow velocity of slope flow decreased by 47.85%, 53.86%, 57.69%, and 60.11%, respectively. 3) The slope significantly dominated the flow index. The inconsistent change was observed in the flow index with the slope under different straw coverage. When the coverage was ≤2.5 t/hm², the flow index increased first and then decreased with the increase of slope. When the coverage was >2.5 t/hm², the flow index decreased gradually with the increase of slope. The flow index of bare slope was ranged from 0.086 to 0.178, whereas, the flow index of straw mulching slope was ranged from 0.247 to 0.766. 4) The Darcy-Weisbach resistance coefficient was negatively correlated with the Reynolds number under the bare slope. By contrast, there was the positive correlation with the Darcy-Weisbach resistance coefficient and Reynolds number under the straw mulching. The Darcy-Weisbach resistance coefficient presented a significant power function relationship with Reynolds number, with the bare slope and straw coverage of 1.5 t/hm². The Darcy-Weisbach resistance coefficient of straw covering slope was 9.36-19.68 times higher than that of bare slope.Under different coverage conditions, the variation of Darcy resistance coefficient with slope is different. Furthermore, the Darcy-Weisbach resistance coefficient reached the maximum at 10° slope under the low coverage (≤2.5 t/hm²). In the high coverage (≥3.5 t/hm²), the Darcy-Weisbach resistance coefficient increased with the increase of slope. The Darcy-Weisbach resistance coefficient shared a power function relationship with the Froude number. This finding can provide a scientific basis for the dynamic mechanism of the slope water erosion process under different straw coverages. [ABSTRACT FROM AUTHOR]

The rod in the composite insulator is a load-bearing component, and glass-fiber-reinforced plastic (GRP) has always been regarded as the most suitable material. However, the investigation reveals that the performance shortcomings of GRP rods are the main cause of emergency heating defects of 131 new 500-kV ac composite insulators in South China. The finite-element simulation is conducted to understand the potential mechanism of heating. It is demonstrated that the holes with moisture distort the electric field, increasing heating power. A hole with moisture in the GRP rod longer than 500 mm could lead to emergency heating defects with temperature rise exceeding 5 K. For the holes in the GRP rod are formed by adjacent voids, the emergency heating defect is inevitable unless the porosity decreases. The fiber infiltration process of the GRP rods is analyzed on the basis of Darcy’s Law, and an improved process is proposed to reduce porosity. Maintaining the mass fraction of fiber by at least 70% and replacing the damp infiltration fluid in time in the production of GRP rods are necessary to restrain porosity. 300-h water diffusion test with a 50- $\mu \text{A}$ threshold is an effective evaluation method of the GRP rod performance. This method should be used before putting composite insulators into operation. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Hydrogeological parameters are main uncertainty source of physical methods • Lag effect of the thick vadose zone limits WTF and dating-based methods • Ignoring the mixing and dispersion may overestimate recharge by 36–48 % for CFC • Aquifer heterogeneity reduces the potential of 14C for recharge estimation • CMB is recommended as the optimal method for GR estimation in the loess area Groundwater recharge (GR) can be estimated with physical, tracer techniques and numerical modelling; however, the uncertainties in these methods have not been fully interpreted. This study selected six methods for actual GR estimation in the saturated zones with different data requirements and method assumptions, including two physical methods (i.e., water table fluctuation WTF and Darcy's law DL) and four tracer techniques (i.e., chloride mass balance CMB, tritium renewal rate TRR, chlorofluorocarbons CFC and 14C dating method CBD). Taking the loess tablelands of China as an example study area, we first analyzed the uncertainties in these methods and then recommended the appropriate methods for GR estimation in regions with thick vadose zones. Overall, the recharge rates from WTF, CMB and CFC (88 ± 24, 98 ± 33 and 53 ± 9 mm/year) were much greater than those from DL, TRR and CBD (10 ± 3, 14 ± 3 and 7 ± 5 mm/year). The differences in estimated GR are closely related to the method parameters, assumptions and temporal scales. Specifically, the model parameters (e.g., specific yield, hydraulic conductivity) exhibit large ranges due to spatiotemporal heterogeneity, and the physical methods are more sensitive to hydrogeological parameters compared with the tracer techniques. The uncertainties related to model assumptions originate from the simplified water/solute movement processes. The lag effect of the thick vadose zone largely limits WTF and TRR, but contributes to CMB. Ignoring the mixing and dispersion effect may overestimate recharge by 36–48 % for CFC, and the heterogeneity of the aquifer reduces the potential of CBD for recharge estimation. Overall, CMB is considered as the most optimal method for estimating GR in the thick loess deposits. This study deepens the understanding of the uncertainties in GR assessment methods in regions with thick vadose zones. [ABSTRACT FROM AUTHOR]

When the Yellow River flows through Togtoh, north China, a puzzling phenomenon occurs, one side is the Hobq desert, and the other side of the river is a lush landscape of gardens. No theory can explain the desertification beside a river. Especially the river might be the main factor in the desertification. We address this challenge by establishing a mathematical model that can depict the different effects of the river and mountain on the river's both sides. The model herein takes into account the different meteorological parameters and soil parameters of the river’s both sides and Earth surface's morphology. Moreover, though our focus is put on the Hobq desert, the present theory on mountain-river-desert relation can also be used for combating desertification. We anticipate that the mountain-river-desert relation is much more important than vegetation restoration and human activity. [ABSTRACT FROM AUTHOR]

Pumped storage power stations are increasingly constructed around cities to provide electric power and ensure grid stability. However, the upper reservoirs are typically located on mountaintops, and the reservoir leakage, which directly affects the economic benefits, is typically difficult to estimate. Therefore, to calculate the leakage within a short period, a one-dimensional simplified analytical method for estimating the leakage of pumped storage power station reservoir basins is proposed based on the stable seepage theory and Darcy's law. Formulae are derived to calculate the seepage flux of the reservoir basin with different groundwater levels, which can be below or above the bottom of the reservoir basin. The reliability of this analytical method was validated using numerical analysis with regard to a pumped storage power station in China, and the relative errors between the analytical results and the numerical results are less than 5%. The proposed method is beneficial for engineering decision-making and design before the construction of pumped storage power stations. [ABSTRACT FROM AUTHOR]

Renewable and carbon free energy relates to the sustainable development of human beings while hydrogen production by renewables and hydrogen underground storage ensure the stable and economic renewable energy supply. A hybrid energy system combining hydrogen production by offshore wind power with hydrogen storage in depleted oil reservoirs was constructed along with a mathematical model where the Weibull distribution, Wind turbine power function, Faraday's law, continuity equation, Darcy's law, state equation of real gas, Net Present Value (NPV) and the concept of leveling were adopted to clarify the system characteristics. For the case of a depleted oil field in the Bohai Bay, China, the annual hydrogen production, annual levelized cost of hydrogen and payback period are 2.62 × 106 m³, CNY 34.6/kgH 2 and 7 years, respectively. Sensitivity analysis found that the wind speed impacted significantly on system NPV and LCOH, followed by hydrogen price and stratum pressure. • A novel hybrid energy system for hydrogen production and storage was built. • The hydrogen was produced by offshore wind while stored in the depleted reservoir. • The H 2 production and CO 2 reduction were 2.6 × 106 m³ and 6.9 × 105 kg annually. • The system NPV and payback period were CNY 1.1 × 108 and 7 years. • Wind speed, H 2 price and stratum static pressure impacted the most on system NPV. [ABSTRACT FROM AUTHOR]

Permeability is one of the most important parameters for accurately predicting water flow in reservoirs and quantifying underground water inrush into coal mines. This study developed a predictive permeability model by considering the microstructural parameters and tortuosity effects of low-permeability sandstone. The model incorporates the fractal geometry theory, Darcy's law, and Poiseuille equation into a multistep inversion framework for systematic interpretation of sandstone scanning electron microscopy (SEM) images. A threshold segmentation algorithm is applied to transform SEM images into binary images. Then, we used an improved statistical algorithm with binary image data to estimate the geometric parameters of each pore, such as the perimeter and area. The fractal parameters of pore microstructure were determined by fitting the data of pore perimeters and areas. Finally, the effects of tortuosity on microscopic percolation were considered, and a conventional model was modified for quantifying the relationship between microscopic pore structures parameters and macroscopic permeability. Eight groups of sandstone samples from the Xingdong coal mine in North China were collected for estimating permeability by the developed inversion framework. A direct permeability measurement was also conducted on each sample with an AP-608 automatic measuring instrument. The measured permeability values were compared with results from theoretical models, and we found that the accuracy of the newly developed predictive model is better than that of a conventional permeability model. The predictive model developed in this study provides a useful tool for estimating permeability in low-permeable sandstone reservoirs. [ABSTRACT FROM AUTHOR]

The complexity of unsaturated soil means that its permeability coefficient and seepage law are important topics in soil mechanics and geotechnical engineering. In this study, a new type of equipment for measuring the seepage of unsaturated soil was used to study the steady seepage of unsaturated loess soil collected from northern Shaanxi province in China. The entire process of the steady seepage of unsaturated soil under different seepage hydraulic gradients was obtained, and the permeability coefficient in the steady seepage state was measured. When the soil water content was low, the soil moisture remained only in small pores or at the junction of soil particles, the effective seepage area of the sample was reduced, and the seepage path was extended. Therefore, the lower the water content, the smaller the permeability coefficient of unsaturated soil and the longer the time required for the seepage to reach a steady state. The matric suction of the unsaturated loess soil was measured under different water contents. With decreasing water content, water remained only in the smaller pores, which provided shrink films with a smaller radius of curvature. This allowed the shrink films to withstand a larger pore air pressure and transmit a smaller pore water pressure, so that the matric suction of the loess soil increased with decreasing soil water content. The Gardner model provided an accurate fit of how the matric suction varied with the volumetric water content of the unsaturated soil. The seepage velocity and seepage hydraulic gradient were correlated well with a linear relationship, indicating that the seepage law of unsaturated loess soil accords with Darcy's law. The experimental results show that the new unsaturated soil permeameter has good performance and controllability, thereby providing support for studying the steady seepage of unsaturated soil. [ABSTRACT FROM AUTHOR]

The movability of water in shale nanopores intensely affects the transport and storage of other fluids and plays an important role in the geological water cycle. To investigate the movability of water, three shale samples were used to conduct flow experiments using the steady state and step‐by‐step depressurization method. The experimental results show that the movability of water strongly depends on the pressure gradient. Two water‐related mechanisms, shear fluidity and electroviscous effect, are primarily responsible for the difference in movability between free water and bound water. The flow of water in these samples deviates from Darcy's law, and the threshold pressure gradient (TPG) is observed. When the pressure gradient is higher than the TPG, water starts to flow, and the permeability increases with increasing pressure gradient. Based on the analysis of the solid‐liquid interfacial forces, the water in the shale was quantitatively classified into four types (L1, L2, L3, and L4) according to its movability. The calculation results indicate that most of the water, which could be up to 74.46–89.73%, is immovable under the experimental conditions. The proportion of movable water increases with increasing pressure gradient, and the relation can be expressed by a quadratic function. The moving ratio was defined as the ratio of the volume of water involved in flow to the total pore volume. The correlation between the moving ratio and permeability is a power function with exponents ranging from 1.16 to 1.43, indicating that water permeability is sensitive to the moving ratio. Key Points: The TPG was investigated and discussed, combining the step‐by‐step depressurization experimental method and DLVO theoryThe distribution and proportion of water with four different movability are analyzed based on the solid‐liquid interfacial forcesThe increase of moving ratio of water in shale nanopores with the pressure gradient leads to an increase in water permeability [ABSTRACT FROM AUTHOR]

• Municipal solid waste (MSW) can be reduced with mechanical biological treatment (MBT). • Effects of various factors on the permeability coefficient of MBT waste were studied. • The permeability coefficient was found to be inversely related to the pressure. • The test MBT waste from China showed some differences with that from other countries. • New techniques to improve the safety of MBT waste in landfills would be useful. Mechanical biological treatment (MBT) can greatly reduce the amount of municipal solid waste (MSW) and has become a hot topic in environmental geotechnical engineering. To study the effects of factors such as the pressure, dry density, compression time under pressure, strain, and hydraulic gradient, permeability tests with saturated MBT waste were conducted by using a compression and permeability combined apparatus in an environmental geotechnical laboratory. The results showed that Darcy's law was applicable to the saturated MBT waste. The permeability coefficient was found to be inversely related to the pressure, dry density, compression time under pressure and strain. The logarithmic permeability coefficient and the variables (e.g., pressure) could largely be fitted to a linear function. Additionally, a prediction model for the permeability coefficient was established, and the permeability coefficient at different depths of MBT landfills was predicted. The results were then compared to previous studies on MSW and MBT waste to investigate the permeability mechanism. [ABSTRACT FROM AUTHOR]

In-depth studies on soil water storage in red soil slopes in south China are of important scientific significance and practical application value for flood control, drought relief and conservation of soil and water. Agricultural cultivation under the fruit forest is an important way of development and utilization of red soil slopes in southern China, and the properties of top-layer soil would be affected by biological process, soil erosion, artificial tillage, etc. Hence, it is essential to understand difference of top-layer soil hydraulic characteristics of several agroforestry systems, which may affect soil water storage. The study area lies in Jiangxi Provincial Eco-Science Park of Soil and Water Conservation (115°42′38″-115°43′06″ E、29°16′37″-29°17′40″ N), which is located in De'an County, Jiangxi Province, China and belongs to Boyang River watershed of Poyang Lake Basin. A total of 4 treatments of agroforestry systems, namely, agriculture-forestry-grass, protective farm-forest, common farm-forest, and pure forest were studied. The top layer was defined as 0-0.30 m subsurface depth in this paper, and soil samples of the top-layer soil were collected by foil sampler for each plot. For each sample, the bulk density was measured by drying method, water retention curve was test by pressure membrane meter, and saturated hydraulic conductivity was measured by saturated infiltration experiment. The van Genuchten-Mualem model was used to describe water retention curve, and the other 4soil hydraulic parameters were reciprocal of air entry pressure, grain size distribution parameter, saturated soil water content, and residual soil water content besides saturated hydraulic conductivity. The one-dimensional Richards' equation based on the Darcy's law was used to describe soil water flow due to its solid physical foundation, and the Ross method was used to solve the Richards' equation owing to the higher computational efficiency and accuracy. For the sake of simplicity, several assumptions were considered for simulation. Firstly, the difference of top-layer soil hydraulic characteristics was the only various factor of the 4 plots, and the soil profile for simulation was also divided into 2 layers, and the top layer was from soil surface to 0.30 m depth. Secondly, the simulation period was set to from August 1st to December 31st, 2010 since runoff wasn't observed in this period. Thirdly, the upper boundary condition was considered as atmospheric boundary condition, where the potential evaporation was calculated by Penman-Monteith model. Besides, the lower boundary was zero-flux boundary at 1.00 m depth where was impermeable bedrock. The statistical analysis results of soil hydraulic parameters showed the most significant difference between top and deep layer in agriculture-forestry-grass soil with the lowest viscosity and highest permeability, i.e., the largest saturated hydraulic conductivity and reciprocal of air entry pressure among the 4 plots. Correlation analysis of parameters showed that absolute of correlation coefficient between saturated hydraulic conductivity and bulk density and that between reciprocal of air entry pressure and bulk density could reach to 0.96. The distribution of soil water content of each profile was simulated, and soil water storage was calculated by the simulated soil water content. The simulation results showed the order of soil water storage under the 4 treatments from high to low as followed: agriculture-forestry-grass soil, protective farm-forest soil or common farm-forest soil and pure forest soil. The simulation results during specified periods indicted the mechanism of effects of top-layer soil hydraulic characteristics on soil water storage. For agriculture-forestry-grass soil, the top-layer soil cut off the upward movement channel of soil moisture to reduce the water consumption of the deep soil during the evaporation period, while the top-layer soil increased the downward movement to enhance the water storage of deep soil. In conclusion, agriculture-forestry-grass is worth of development and promotion in red soil slopes in south China. [ABSTRACT FROM AUTHOR]

Toe-to-Heel Air Injection (THAI) is a great potential in improving energy efficiency for heavy oil/bitumen recovery. A 3D cylindrical combustion model with large size is used to carry out several experiments using Xinjiang (China) crude oil. The evolution of the fire chamber, temperature variation rate, and mass of burned carbon were analyzed using temperature measurements and flue gas composition analysis. Coke zone was quantified in the variation of zone thickness and distribution characteristics. The results reveal that there is a prevailing stable propagation of the combustion front during the first one third of the process for varying injector to producer spacing. Oxygen breakthrough is more susceptible for smaller separations and the combustion zone is reduced in length. Larger combustion fronts with greater relative propagation in the horizontal direction occurs when the well spacing is larger. The distribution of coke is significantly influenced by the injector/producer spacing. For a THAI pattern with greater injector/producer spacing, a smaller inclination angle of the coke zone occurs and the likelihood of oxygen breakthrough to the horizontal production well is lessened. Hence, the injector to producer spacing needs to be considered in designing a safe THAI process for potentially larger efficiency and optimum economics. [ABSTRACT FROM AUTHOR]

A newly developed low-velocity non-Darcy flow numerical simulator is applied to the Fuyu formation. The three-dimensional geological model of subject reservoir was established and 9 well plans were designed to obtain the optimal well adjustment plan. Additionally, the formation pressure gradient distributions were provided and the flow regions were divided to study the adaptability of different well adjustment plans. The numerical simulation of Da45 reservoir is an excellent opportunity to: (1) put the non-Darcy flow numerical simulator into application, (2) provide guidance for the Da45 reservoir, and (3) provide reference to the non-Darcy flow numerical simulation technique. [ABSTRACT FROM AUTHOR]

There exist many fluvio-glacial deposits in the valley of Dadu River, Southwest China, which dates back to the Pleistocene. As some of the deposits are located within the seasonal water fluctuation zone of reservoirs, the seepage of groundwater acts as one of the key factors influencing their stability. Investigation into the sediment properties and permeability is, therefore, crucial for evaluating the sediment stability. In this study, in-situ permeability and sieving tests have been carried out to determine grain size distribution, correlations of permeability and hydraulic gradients, and relations between permeability and sedimentation properties. Test results indicate that the deposits are composed mostly of sands, gravels, cobbles and boulders, and the percentage of fines is less than 5%. The sediments have high densities, low porosities and natural moisture contents. At low hydraulic gradients, the seepage velocity obeys the Darcy's law, while a non-Darcy permeability is observed with hydraulic gradient exceeding a certain value (about 0.5-0.7). The linear permeability coefficient ranges from 0.003 to 0.009 cm/s. Seepage failure occurs above a threshold between 1.1 and 1.5. The test data fit well with the non-linear permeability equations suggested by Forchheimer and Izbash. The non-Darcy permeability proves to be in accordance with the seepage equation suggested by Izbash with the power ' m' of about 0.6-0.7. The characteristic grain sizes of the studied deposits are found in a narrow range between 0.024 and 0.031 mm, which is much lower than the effective grain size ( d). [ABSTRACT FROM AUTHOR]

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This article presents a concept of critical thickness in low permeable coalbed methane reservoirs with a simulation study when a horizontal well is used. The equations proposed to finish the simulation study are based on the Langmuir equation, Fick pseudo-steady state law, and Darcy equation, in which equivalent radius model and function of pseudo pressure are combined to consider the effect of diffusivity and compressibility. The method of finite difference is presented to solve the equations. Then we established the partial differential equations and the definite conditions that describe the mechanism of coal gas and water flow. As the low permeable property of a coal bed in China, we discussed the applicability of a horizontal well according to the reservoir thickness. The significant results from our study include: (1) There is critical reservoir thickness in developing low permeable coalbed methane reservoir with horizontal well. (2) When the thickness is less than the critical value, the cumulative gas production will be lower and the commercial efficiency is unsatisfactory. When the value is more than the critical one, the productivity will not increase as quickly as the reservoir thickness. On the contrary, it will be almost stable along with the reservoir thickness increase. (3) The production effect of the horizontal well on a low permeable coalbed methane reservoir will be decreased when the reservoir thickness is too high. (4) The peak gas rate will go down first and move upward later as the reservoir thickness increases. Consequently, the adaptability of the horizontal well to a low permeable coalbed methane reservoir should be analyzed first according to the reservoir thickness. [ABSTRACT FROM AUTHOR]

Abstract: The complicated mechanisms governing hydrocarbon expulsion (primary migration) have not as yet been fully understood, though understanding these mechanisms is paramount in basin modeling. This paper presents (a) a simple oil-expulsion model based on the principles of sedimentary compaction and the flow difference between oil and water, and (b) a simple gas-expulsion model via mass balance. These two models do not consider more factors or mechanisms than some existing models, but we verify that the predicated expelled amount is proper by using it as input data for secondary migration and confirming that the modeled volume of accumulated hydrocarbons is close to that determined by exploration. The hydrocarbon migration–accumulation (secondary migration) history is the most important component in basin modeling, but it is also one of the most challenging to achieve. In general, a sectional 2-D simulator cannot predict the amount of hydrocarbon accumulated, whereas a 3-D simulator takes considerable computing time. This paper presents a simplified pseudo 3-D model based on the principles of buoyancy drive and Darcy''s Law in combination with the effects of faulting and lithology on migration pathways. Comparing with the existing four models currently in use (multi-phase Darcy flow, flowpath, hybrid method combining the former two approaches together, and invasion percolation), the proposed model is mainly targeted at calculating the quantities and locations of petroleum accumulations for oil and gas assessment, and so the factors taken into account and the functions needed to be executed in software are less than in other models. Application of the aforementioned three models in the Kuqa Depression of the Tarim Basin in western China shows that the simplified pseudo 3-D model is very efficient and less computationally extensive, and the predicted quantities and locations of petroleum accumulations approach those determined by exploration, showing these models could form a useful prospecting method. [Copyright &y& Elsevier]

The article presents a study on the special cavities and fractures of the Tahe-fractured reservoir in Xinjiang Autonomous Region in China. It notes that the reservoir cannot be regarded as a traditional continuous porous medium, and therefore, a Darcy-Stokes compound single-porosity model was created, with entire flow area divided into a Darcy-Flow region. Accordingly, the model has successfully showed the flow behavior of bottom and edge water that flow into the wellbore within the cavity.

There are ∼470,000 km2 of karst aquifers that feed many large springs in North China. Turbulent flow often exists in these karst aquifers, which means that the classical ground water model based on Darcy’s law cannot be applied here. Ground water data are rare for these aquifers. As a consequence, it is difficult to quantitatively investigate ground water flow in these karst systems. The purpose of this study is to develop a parsimonious model that predicts karst spring discharge using gray system theory. In this theory, a white color denotes a system that is completely characterized and a black color represents a system that is totally unknown. A gray system thus describes a complex system whose characteristics are only partially known or known with uncertainty. Using this theory, we investigated the karst spring discharge time series over different time scales. First, we identified three specific components of spring discharge: the long-term trend, periodic variation, and random fluctuation. We then used the gray system model to simulate the long-term trend and obtain periodic variation and random fluctuation components. Subsequently, we developed a predictive model for karst spring discharge. Application of the model to Liulin Springs, a representative example of karst springs in northern China, shows that the model performs well. The predicted results suggest that the Liulin Springs discharge will likely decrease over time, with small fluctuations. [ABSTRACT FROM AUTHOR]

Tarim Basin, Western China has newly discovered fracture-caved carbonate reservoirs formed by large-scale fault tectonic activity and multiple-stage karstification. The large karst caves interconnecting with tectonic fractures in series to form vertical beads-on-string structure is one of the most common patterns. Moreover, the situations of wells drilled into caves often occur during drilling. The complex geological and engineering factors cause that traditional continuum-flow models are difficult to match the recorded pressure data. To present a novel well test model to reasonably estimate reservoir parameters, this work first presents a multi-cave multi-fracture series connection physical model by simplifying complex vertical beads-on-string structure. Four kinds of mediums are considered in physical model, including large caves, small vugs, high-angle tectonic fractures and rock matrix. Thereafter, the multi-cave-multi-region model for wells drilled into vertical beads-on-string caves is developed, among of which the flow in fracture regions obeys the Darcy's law, while the flow in large caves is assumed to obey free flow. Particularly, gravity effect is considered in fracture regions because the fluids flow along vertical structure. Then we analyze the typical flow regimes and conduct sensitivity analysis on crucial parameters. Results indicate that (a) the new cave storage regimes, characterized by unit-slope pressure-derivative curve, are recognized. This may help identify large karst caves in field case analysis; (b) The typical feature of vertical beads-on-string structure on type curves is that cave storage regimes and linear flow regimes alternately appear; (c) large cave and vug can be distinguished by the slope of pressure derivative on type curves; (d) gravity effect could lead to unit-slope pressure and pressure derivative curves, which is traditional recognized as the presence of a closed boundary when it may not be the case. Finally, three field cases from Shunbei Oilfield in which it is difficult to achieve good fitting quality using traditional models are interpreted to verify the practicability and feasibility of the proposed model. • The multi-cave-multi-region model for wells drilled in vertical beads-on-string caves is developed by coupling the free flow and Darcy flow. • The new cave storage regimes, characterized by unit slope on pressure-derivative curve, are identified, which help determine large karst caves. • Large cave and vug can be distinguished by the slope of pressure derivative on type curves. • Gravity effect is difficult to be observed from well test curves with on more than two-week test duration. [ABSTRACT FROM AUTHOR]

Seasonally frozen soil where uneven freeze–thaw damage is a major cause of highway deterioration has attracted increased attention in China with the rapid development of infrastructure projects. Based on Darcy's law of unsaturated soil seepage and heat conduction, the thermal–hydraulic–mechanical (THM) coupling model is established considering a variety of effects (i.e., ice–water phase transition, convective heat transfer, and ice blocking effect), and then the numerical solution of thermal–hydraulic fields of subgrade can be obtained. Then, a new concept, namely degree of freeze–thaw damage, is proposed by using the standard deviation of the ice content of subgrade during the annual freeze–thaw cycle. To analyze the freeze–thaw characteristics of highway subgrade, the model is applied in the monitored section of the Golmud to Nagqu portion of China National Highway G109. The results show that: (1) The hydrothermal field of subgrade has an obvious sunny–shady slopes effect, and its transverse distribution is not symmetrical; (2) the freeze–thaw damage area of subgrade obviously decreased under the insulation board measure; (3) under the combined anti-frost measures, the maximum frost heave amount of subgrade is significantly reduced. This study will provide references for the design of highway subgrades in seasonally frozen soil areas. [ABSTRACT FROM AUTHOR]

There are numerous percolation studies of unconventional reservoirs showing that in tight or low-permeability formations, the oil flow behavior could be described by the Pre-Darcy mechanism. However, for the CO 2 Huff-n-Puff operations, the most presented low-velocity Pre-Darcy flow models may result in an erroneous evaluation due to the intensive boundary layer thickness changes caused by the CO 2 extraction and dissolution. In this paper, with multiple parameters fitting the seepage experimental results of the studied area, a unified dimensional Pre-Darcy flow model for CO 2 enhanced oil recovery (EOR) is derived from the classic Poiseuille model. Then, the proposed flow model is applied in the compositional simulator for analyzing the viscosity-dependent boundary layer (VDBL) effect, applicability evaluation in Huff-Puff EOR, and field history matching. The results indicate that the VDBL effect improves the oil mobility in injection periods and lowers the residual oil saturation at the front of the CO 2 convection-diffusion area in reproduction periods. Additionally, the nonlinear parameter α and the shape parameter β enhance the proposed model's applicability for the Huff process and the Puff process respectively. Finally, by adjusting the parameters α and β for different permeability intervals of the geological model, the flow model is successfully applied in the oil production matching of the Y6 well, which exhibits its reliability in the history matching. • A unified dimensional flow model is derived from the classic Poiseuille model to characterize the oil seepage behavior. • The proposed flow model is applied in the compositional simulator for analyzing the VDBL effect. • The flow model is successfully applied in history matching of the Songliao tight field in China to exhibit its reliability. [ABSTRACT FROM AUTHOR]

• We compared 4 methods estimating bare soil evaporation to lysimeter measurements. • The performance was tested under different water table depths. • The maximum entropy production method performed best across different conditions. • The extinction depth is a first-order indication on the performance of three methods. • We suggest determining the extinction depth as part of evaporation studies. Evaporation from bare soil is an important component of a catchment water balance. However, it is arguably one of the most challenging hydrological processes to estimate and measure accurately. Several approaches to estimate soil evaporation exist, but their performance for specific water table conditions remains unclear. This study investigated the performance of four commonly used approaches and several ways on how to implement them: the energy-balanced based FAO-56 method with the skin evaporation enhancement (FAO-56 skin), hydraulic methods based on groundwater level fluctuation (GLF), Darcy's law, and the maximum entropy production (MEP) method based on non-equilibrium thermodynamics theory. Three lysimeters with different water table depths were used at a research site in the Guanzhong Basin of China. The lysimeters were equipped with soil moisture probes. Water table fluctuations were also measured. The data allow us to accurately estimate evaporation rates using a water balance approach and are used to assess the performance of the analysed methods. The results show that: (1) The MEP method performed best for all water table conditions, but tends to overestimate evaporation if the water table is below the extinction depth. The extinction depth is the depth of the water table were there the contribution of groundwater to bare-soil evaporation is zero. In our case, the extinction depth was 78 cm. (2) The FAO-56 skin method underestimated evaporation where the water table was above the extinction depth, and vice versa. (3) The groundwater level fluctuation method significantly overestimated the evaporation if the specific yield was estimated using hydraulic methods. The groundwater level fluctuation method should be combined with a soil water balance, independent of water table conditions. The method can only be applied if the water table is above the extinction depth. (4) Conceptually, Darcy's law was suitable for estimating evaporation. However, the estimation of the required parameters is challenging. A good fit could only be obtained through calibration to measured evaporation rates. [ABSTRACT FROM AUTHOR]

Determining the optimal well types for ground development of coalbed methane (CBM) is a significant premise from which to reduce construction risk during a project and improve CBM production efficiency. Based on Langmuir isotherm adsorption theory and Darcy's law, the research established mathematical models for productivity of vertical wells and stage-fractured horizontal wells, respectively. In combination with the economic evaluation model, the research proposed an optimisation method for CBM wells through productivity prediction, evaluation of comprehensive economic benefit, and well-type determination. Then, the method was verified based on practical reservoir conditions and CBM production of the developed wells in middle and south of Qinshui Basin (Shanxi Province, China). Meanwhile, charts of CBM production under influences of gas content and post-fracturing permeability using vertical wells and stage-fractured horizontal wells, respectively. The results indicate that, in the Shizhuang south block, when the gas content is less than 10 m3/t, CBM wells are not recommended; If the gas content is between 10 and 12 m3/t, stage-fractured horizontal wells can be constructed in areas where post-fracturing permeability can exceed 1.27 × 10−3μm2, faults and collapse columns were not developed, and hydrogeological conditions were not complicated; If the gas content is between 12 and 15 m3/t, stage-fractured horizontal wells can be constructed except in areas of mylonite coal; For reservoirs with gas contents between 15 and 18 m3/t, stage-fractured horizontal wells are preferred, and vertical wells can be considered in areas where post-fracturing permeability can exceed 0.91 × 10−3μm2, faults and collapse columns were not developed; In the case that the gas content exceeds 18 m3/t, both types of wells can be constructed, except in areas of mylonite coal. The results allow us to select a suitable method for selecting CBM well types under different reservoir conditions. • Establish mathematical models for productivity of vertical and horizontal wells. • Establish an economic evaluation model of CBM wells. • Plot charts for the relationships of gas content and permeability and gas production. • Propose a method for determining the well types of CBM development. [ABSTRACT FROM AUTHOR]

The groundwater flow in karst aquifers is prone to become non-Darcian due to the presence of karst conduits, and this effect may become more pronounced during tunnel construction. Prediction of discharge into tunnels in karst aquifers remains a challenging task because of the complex nature of non-Darcian flow and the uncertainty of aquifer's properties. This study aims to evaluate the effect of non-Darcian flow on the discharge into a tunnel in karst aquifers in Guizhou Province, China, where a large proportion (~86%) of borehole packer tests evidences the flow in non-Darcian regime. An integrated method combining packer test data interpretation, statistical correlation and inverse modelling is proposed to determine the non-Darcian flow properties of the aquifer system. Numerical simulations of steady-state flow show that the predicted discharge based on the Forchheimer's equation agrees better with measurements than that based on the Darcy's law by ~27%. The region with the most pronounced non-Darcian effect occurs at the intersection between the tunnel and a karstified fault connecting to an underground river, and the occurrence of non-Darcian flow leads to an increase in hydraulic gradient, but a reduction in discharge into the tunnel. This work presents a framework that combines aquifer properties estimation and numerical simulations for more accurately evaluating the discharge and seepage erosion risk induced by tunnel construction in karst aquifers. • Borehole packer test data evidence non-Darcian flow behavior in karst aquifers. • Determine aquifer properties by test data interpretation and statistic correlation. • Neglecting the non-Darcian flow effect overestimates tunnel discharge by ~27%. • Increase of flow nonlinearity leads to higher hydraulic gradient and erosion risk. [ABSTRACT FROM AUTHOR]

Unconformities are special geologic bodies with a three-layer structure including the rock above the unconformity, a weathered clay layer, and a leached rock. The Upper Wuerhe (Upper Permian) bottom unconformity in Northwest Junggar Basin is the main pathway system linking the Zhongguai (ZG) lift with hydrocarbon source kitchens. Based on the log response characteristics of the unconformity's vertical structure and core calibration, a principal component analysis (PCA) was applied to extract and identify the evaluation parameters of the unconformity's vertical structure. On the basis of Darcy's Law, the quantitative characterization formula of the unconformity's transport capacity with an actual geological significance was established after taking several factors into consideration. The migration probability of the unconformity was used to evaluate the possibility that the unconformity acted as a migration pathway. Consequently, a relationship between the migration probability and the evaluation parameters was developed to analyze the effectiveness of these parameters in characterizing the transporting capacity of the unconformity. This study shows that the quotient of the two principal components extracted from the conventional logging curves (Pc1/Pc2) have different reference values in the leached and parent rocks. The distribution of thicknesses of the weathered clay layer and the leached rock is well matched with the distribution of paleogeomorphology. The parameters representing only a single geological factor are not enough to determine whether the unconformity acted as a migration pathway. The flow coefficient (C f) containing multiple factors can effectively and clearly identify the transporting capacity of the unconformity, considering the positive correlation between the parameter C f and the migration probability of the unconformity. The oil and gas shows of the area with a parameter C f greater than 10 × 10−4 cm2/s are abundant, which is the superior transporting area of the unconformity, and there is a good matching relationship between the distribution of the superior transporting area of the unconformity and that of the hydrocarbon distribution. • Unconformities are special geologic bodies with a three-layer structure. • The boundary of leached rocks and parent rocks can be effectively identified by the PCA from geophysical log data. • We establish the quantitative evaluation parameter of transporting capacity of unconformities. • Geoparameters pertinent to an unconformity are assessed for characterizing transporting capacity. [ABSTRACT FROM AUTHOR]

This study develops fractal models to incorporate with the empirical Posenille's formula and Darcy's law for deriving a novel relationship between permeability and porosity that includes fractal dimensions. To test this relationship, we performed scanning electron microscopy (SEM) on sandstone samples collected from Xingtai coal mines in Northern China. The image processing software was applied for estimating different statistical parameters (e.g., fractal dimensions) and geometrical parameters. An automated porosimeter-permeameter was developed to measure porosity and permeability of samples. We compared the estimated permeability with the measured permeability data to test the derived relationship. We also developed a neural network model, parametrized by fractal dimensions and porosity data, to estimate permeability. The estimated permeability and the measured ones were compared to assess the accuracy of the neural network model. The results from this study provide substantial insights for understanding the petrophysical properties of the sandstone and other porous rocks. [ABSTRACT FROM AUTHOR]