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To investigate the development of temperature fields under seepage conditions for pipe curtain freezing method, drawing on the Sanya River Estuary Trench Tunnel freezing project, combined with Darcy's law and heat transfer theory in porous media, using finite element software to establish a coupled water-heat numerical model, the study employs varying seepage rates in the model and a method for creating temperature measurement paths, and analyzes the evolution of the frozen soil curtain, circulation time, and wall thickness. The results indicate that the frozen soil curtain develops along the seepage direction, with the soil on the downstream side freezing earlier than the upstream side, and attaining a lower final temperature； when the flow rate is approximately 2. 87 m/d, the impact of low seepage rates on the overall circulation time of the frozen soil curtain is relatively minor； as the seepage rate increases, the overall circulation time of the frozen soil curtain grows significantly, accompanied by increased regional unevenness and a decrease in thickness； when the flow rate increases to approximately 10. 02 m/d, local non-circulation occurs in the frozen soil curtain. Considering the original freezing plan to be conservative, an optimized design is proposed： reducing the number of inner circle freezing pipes from 80 to 56, the simulated average thickness of the frozen soil curtain is approximately 4. 28 m, a decrease of 0. 195 m compared to the original plan. This optimized design still meets the freezing design specifications. [ABSTRACT FROM AUTHOR]

Multistage fracturing is a commonly-used method to improve gas production in tight hydrocarbon reservoirs. Stress shadowing effect among multi-fractures is crucial in effectively connecting the pre-existing natural fracture of reservoir and forming a complex fracture network that facilitates gas flow. Challenges remain in accurately characterizing the fracture structure and propogation patterns of naturally fractured reservoirs. In this study, we adopt an adaptive finite-discrete element method to simulate the multistage fracturing of a naturally fractured reservoir by improving the mesh auto-refinement and identification of multiple fracture propagation. The numerical model covers interactions among hydraulic fractures, pre-existing fractures, and microscale pores, while integrates the nonlinear Carter leak-off criterion to describe fluid leak-off and hydromechanical coupling effects during multistage fracturing. We introduce the proppant transport equation for idealised parallel plate flow in fractures, and Darcy's law is adopted to analyse the seepage flow in the fracture network and determine gas recovery. We then compare the fracture network and consequent fluid flow induced by the hydrofracturing of unfractured and naturally fractured models to assess the influence of pre-existing fractures on multistage fracturing behaviour and gas production. This study provides a new approach to determine and optimize fracturing cluster spacing in tight gas reservoirs. [ABSTRACT FROM AUTHOR]

The permeability coefficient of coal seams is a key parameter that judges the difficulty of gas flow in coal seams. In the current calculation formula for the permeability coefficient of coal seams, the coefficient of the nonlinear partial differential equation with variable pressure is assumed to be a constant, which leads to significant errors in the theoretical derivation results and results in significant deviations in the permeability coefficient measured on site. To solve the inaccurate determination problem of the coal seam permeability coefficient, this paper derived the process of using the radial flow rate method to test the coal seam permeability coefficient, and pointed out the problems of this method during the derivation process. Based on the Langmuir's gas content and Darcy's law, a dimensionless model was established, and the model solution results were inverted and fitted. A new calculation formula for the coal seam permeability coefficient was obtained, which was verified by on-site drilling data. The current testing method for coal seam permeability coefficient was revised, and an accurate and reliable new method for calculating the coal seam permeability coefficient was proposed. The results indicate that using a parabolic equation to represent the coal seam gas content and treating variable p1.5 as a constant to derive the coal seam permeability coefficient calculation formula is equivalent to fitting the gas content into a proportional relationship with the square of pressure. There are theoretical problems and significant errors in actual calculations. Using the Langmuir dimensionless model to calculate Y' for inversion fitting can solve the shortcomings of current calculation methods. When the product of the adsorption constant b and the original gas pressure p0 (the dimensionless original gas pressure) is different, the function curve of the dimensionless gas emission velocity Y' and the dimensionless time Fo' is significantly different. Therefore, the permeability coefficient calculation formula containing the dimensionless original gas pressure was obtained. When the coal seam and drilling conditions are constant, the values of the coal seam permeability coefficient λ calculated from the gas emission volume at different times have a good reproducibility. The new on-site measurement method for the permeability coefficient of coal seams is completely the same as the current method without adding additional workload. However, the new calculating method is more accurate and reliable.

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Based on the permeability-based hydraulic fracture (PHF) model， a statistical fracture model (SFM) is introduced to capture the influence of the micro non-uniform distribution of rock materials on the macroscale characteristics of hydraulic fracture. The Weibull probability model is adopted to account for the discreteness of characteristics of these characteristics. By assuming that the permeability of rock material is a function of the mean effective stress， the PHF-SFM model is proposed based on the Biot consolidation theory. The model incorporates the Mohr-Coulomb elastoplastic constitutive model and Darcy’s law to represent mechanical behaviors for the solid and liquid phase of rock material in pre- and post-failure part. The verification is carried out by comparing the simulated results with those of the KGD model. Breakdown pressure， equivalent fracture height and fracture width were studied by varying the Weibull modulus and scale parameters in the SFM model and material properties of rock. The simulation results indicate that including the SFM model does not affect the breakdown pressure， but does vary the fracture geometry. When the Weibull modulus decreases or the scale parameter increases， the discreteness of fracture geometry features increases. [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]

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]

In order to prevent and solve the "water damage" problem such as seepage blockage under hydrodynamic pressure. Based on experimental grading scheme and Monte Carlo method, the two-dimensional mesoscopic models for three working conditions of OGFC (open graded friction course)-13 asphalt mixes with open-graded anti-slip layers were established. The effects of aggregate particle size and voidage of asphalt mixture as well as hydrodynamic pressure on the permeability of permeable asphalt pavement were simulated analysis from the meso level with the multi-relaxation Lattice Boltzmann method. The results show that the larger the voidage and particle size, the greater the permeability of asphalt mixture; when the hydrodynamic pressure is in the range of 0~1 500 Pa, the average velocity is strictly linear with the pressure gradient, and Darcy's law is applicable. When the hydrodynamic pressure is in the range of 15 000~45 000 Pa, the average velocity acquire by calculation rather large based on Darcy's law. [ABSTRACT FROM AUTHOR]

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In order to study the flow mechanism of gas in coal particles, four groups of constant pressure adsorption experiments were carried out at different initial pressures, and the experimental data of cumulative gas adsorption volume content with time were extracted. Based on Darcy theory driven by pressure gradient and new diffusion model driven by the density gradient of free gas, two kinds of mathematical models of gas adsorption at constant pressure were established, and the adsorption process was numerically solved by VB program code, and the simulation data of cumulative adsorption volume content inside coal particles were obtained. By comparing and analyzing the two kinds of simulation results with the experimental data, it is found that numerical calculation results are consistent with the experimental data, thus verifying the accuracy of the numerical simulation. In addition, the key proportional coefficients in the two models with the change of pressure are different. The permeability coefficient is negatively correlated with the pressure, and the microchannel diffusion coefficient does not change with the pressure. It is concluded that the diffusion model driven by the density gradient of free gas is more suitable to describe the gas migration law in coal particles than Darcy's law and Fick's law.

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Interaction between surface water and groundwater has always been a hot topic in hydrogeological researches. Previous studies focused on the hyporheic zone of rivers, but the hypolentic zone of lakes with relatively static water bodies was seldom examined. The Baiyangdian Wetlands is taken as a pilot area in this study, and a monitoring system of water table and temperature is set up. The vertical interaction fluxes between surface water and groundwater is quantified by using a heat tracing method. According to the Darcy’s Law, the vertical coefficient of permeability is calculated inversely. Based on the heat tracing method and the Darcy’s Law, a way of quantifying vertical interaction between surface water and groundwater is summarized. The results show that infiltration from surface water to groundwater around the banks of the Baiyangdian Wetlands is dominant in the interaction procedure. The total infiltration velocity from surface water to groundwater during the monitoring period ranges from 0.2 to 1.1 cm/d, and the vertical hydraulic conductivity, from 0.038 to 0.912 m/d. The conclusions in this paper can provide data support for strategy of water diversion and protection of eco-environment in the Baiyangdian Wetlands.

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In order to study the influence of long-term rainfall on the southern slope of an open-pit coal mine in Xinjiang, and the variation of pore water pressure in the slope at different periods after rainfall, Darcy’s law and Van Genuchten model and numerical simulation method are used to analyze the stability of the existing slope after rainfall; the research results show that: under the influence of long-term rainfall, the pore water pressure in the south slope of the stope changes little, while the positive pore water pressure appears in the upper slope. The long-term rainfall makes the underground water level rise, the cohesion of the slope decreases, and the shear strength decreases, which leads to the transient safety system of the slope.

Based on a coupled fluid-solid theory, an extended permeability-based hydraulic fracture(EPHF) model was developed according to the permeability-based hydraulic fracture(PHF) model. The proposed EPHF model assumed that the permeability of porous rock was a function of mean effective stress when a rock was fractured. The porous elastic constitutive law and Drucker-Prager plastic model were adopted to model the pre-failure and post-fracture process of rock material, respectively. The Darcy's law was used to describe the liquid phase. To consider the influence of injection fluid, the LET model was integrated to modify the permeability of fracture zone with the mixed viscosity of injection and original fluid being used. The development of pore pressure, stress path, equivalent fracture zone and fracture height for different tensile strength were studied by using the proposed model. The simulation results indicated that the pore pressure in fracture path(except injection point) first decreased and then increased to propagation pressure. If the effective stress difference and pore pressure were kept the same or if the total stress was constant, the breakdown pressure decreased when the effective stress ratio increased. [ABSTRACT FROM AUTHOR]

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Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu 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.)

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The calculation formulas for water inflow of a circular foundation pit with different insertion depths of waterproof curtain are proposed based on the principle of seepage continuity of groundwater and Darcy’s law, The analytical solution of ground subsidence outside the foundation pit with different insertion depths of waterproof curtain is proposed according to the method of resistance coefficient widely used in ship engineering in China, Finally, an applicable procedure of dewatering of foundation pit with waterproof curtain partially penetrating aquifers was developed, in which water control cost is set as the target, and ground subsidence and groundwater inflow are set as the constraints conditions considering both safety and economy of foundation pit design. The proposed optimization method for water control was applied in a project site in Tongzhou district, Beijing. [ABSTRACT FROM AUTHOR]

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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]

After the mining face of low-gas mine is sealed, a large number of free gas gathers in the sealed space.When the quality of the seal drops to a certain extent, the fluctuation of the air pressure out of the sealed goaf will cause"breathing"phenomenon and lead to the gas concentration of the seal’s outside exceed safety limit.No.14-1103 sealed goaf of Zhengli Coalmine is selected as the research object, the variation law on inner and outer pressure of sealed goaf and gas concentration of the seal’s outside are analyzed under different atmospheric parameters. The mechanism of"breathing"phenomenon is theoretically analyzed with ventilation energy equation and state equation of ideal gas, and the expression of relationship between differential pressure and gas concentration is obtained with Darcy law. The results show that, "breathing"phenomenon results from the combining action of ground atmospheric parameters, airflow parameters, roadway characteristics and gas state parameters of sealed goaf.Under the continuous action of differential pressure between seal’s inside and outside, gas exchange will occur between sealed goaf and outside space. The gas pressure in sealed goaf is gradually decreasing or increasing as the differential pressure is positive or negative.The gas pressure in sealed goaf has small change, the fluctuation of static pressure of the seal’s outside is the dominant factor that results in positive and negative alternation of differential pressure.The variation trend of the static pressure of the seal’s outside is similar to that of the ground atmospheric pressure and opposite to that of the ground atmospheric temperature when roadway characteristics and air quantity are stable.On the premise that the seal’s permeability and the air quantity of seal’s outside are relatively stable, the gas concentration is positively correlated with the differential pressure when the positive differential pressure appears, so that, the change trend of gas concentration is similar to that of differential pressure.An automatic control system of gas release, which consists of monitoring signal acquisition subsystem, field automatic control subsystem and pipeline explosion suppression subsystem, is designed to prevent gas concentration of seal’s outside from exceeding safety limit.The joint control criteria is determined based on the threshold values of differential pressure and gas concentration, and the grading control logic of valve opening is put forward. [ABSTRACT FROM AUTHOR]

Liquid transport in yarns is affected significantly by geometry of capillary. In order to investigate the mechanism between the structure of capillary and the liquid transport behavior, an N section lotus-rhizome-node-like non-uniform capillary model was established based on the Darcy's law and capillary pressure equation to investigate the transport of liquid in the capillary of yarns. The wicking height-time equation of the non-uniform capillary was obtained as a function of the height and width ratio between the converging and diverging nodes and their total section numbers. Nylon filament yarns with different twist factor and different single filament fineness were prepared to verify the model. The results indicated that liquid transport velocity greatly depended on the alternate frequency between the converging section and diverging section (i.e. the section number in certain length). The non-uniform capillaries with rapid alternations between converging and diverging nodes have low liquid transport efficiency. The thick capillary exhibits a fast liquid transport efficiency and high balanced wicking height in those capillaries with the same geometry (the same height and width ratio). The experimental results from the twisted Nylon filament yarns agreed fairly well with the theoretical predictions of the N-section lotus-rhizome-node-like non-uniform capillary model. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Heilongjiang University of Science & Technology is the property of Journal of Heilongjiang University of Science & Technology Editorial Department 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.)

Groundwater artificial recharge has been widely used to effectively utilize abundant rainfall in rainy seasons for managing a number of environmental problems such as seawater intrusion and depletion of spring flow caused by groundwater overexploitation. However, physical clogging (including suspended solid clogging and gas clogging) is an important factor that may negatively affects efficiency of groundwater artificial recharge. To tackle the problem of gas-clogging (i. e., a large amount of bubbles contained in artificial recharge water), an indoor device for conducting column experiments is designed. A column is filled with sand of multiple layers, and the hydraulic conductivity of each sand layer is estimated based on the Darcy's law to investigate the processes and mechanisms of gas-clogging development. The laboratory results show that, due to gas clogging, hydraulic conductivity is not a constant but a temporal function of exponential decay. The results also show that gas clogging mainly occurs in the upper layer(0-30 cm)of the sand column, and that the clogging rate decreases gradually with depth. The results suggest that, to reduce the negative effects of gas clogging on efficiency of groundwater artificial recharge, it is necessary to occasionally pause recharge and to conduct degassing during the recharging processes. [ABSTRACT FROM AUTHOR]

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu 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.)

In order to study the coal gas flow law in coal particles, a dynamic gas adsorption experiment under a constant temperature and pressure was conducted in this study. The change curves of cumulative gas adsorption amount over time were obtained which was under different coal sample sizes and different pressures. Based on the Darcy's law and Langmuir equation, a mathematic model of coal gas adsorption was built, and the solver programming was used for the numerical analysis on the process of gas adsorption from coal particle. Therefore, the variation regulation of gas pressure in the inter coal particle and the accumulative adsorption quantity at different pressures were finally obtained. Through comparing the simulation results and experiment results, it concludes that the two change curves match well, and the process of coal gas adsorption in coal particle follows the Darcy's law. [ABSTRACT FROM AUTHOR]

In this paper, based on the generalized Darcy law and fractal theory and the fact that the fractured network may exist in the oil deposit, the starting pressure gradient for Bingham fluids in the fractal disk-shaped branched networks is investigated. The results show that the starting pressure gradient for Bingham fluids is a function of the yield stress and network microstructural parameters such as the branching ratio, the branching angle and the branching number. The function is an analytical formula, which contains no empirical constant. The permeability for Bingham fluids is only dependent on network microstructural parameters and independent of the yield stress. The results also show that the starting pressure gradient decreases with the increase of the diameter ratio and the permeability and increases with the increase of the length ratio. The results have potential applications in petroleum recovering. [ABSTRACT FROM AUTHOR]

In order to study the law of gas desorption and emission, a desorption experiment of coal particles in different sizes under different initial pressures was designed. And the measured curves of gas desorption accumulated amount with the change of time were obtained. According to Darcy law, the paper also built the mathematical model of gas emission which was disposed with finite difference method. The visual Basic language was used to solve and calculate the mathematical model. The variation regulation of gas pressure in the inter coal particle and the accumulative desorption quantity at different pressure are finally obtained. Through comparing the simulation results and experiment results, the conclusion shows that the gas emission from the coal particles corresponds to Darcy law. [ABSTRACT FROM AUTHOR]