scholarly journals Fractal Characterization of Pressure-Relief Gas Permeability Evolution in a Mining Fracture Network

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 7031
Author(s):  
Peiyun Xu ◽  
Shugang Li ◽  
Haifei Lin ◽  
Yang Ding ◽  
Haiqing Shuang ◽  
...  
Keyword(s):  
Gas Flow ◽  
Gas Permeability ◽  
Layer Structure ◽  
Fractal Theory ◽  
Fracture Network ◽  
Average Error ◽  
Overburden Rock ◽  
Permeability Evolution ◽  
Pressure Relief ◽  
Research Results

The process of underground coal mining fractures the overlying strata and may provide storage and transportation space for gas by changing the roof rock permeability, which is released by pressure after mining. This paper adopts the experimental method of physical similarity simulation and combines the fractal theory to study the permeability characteristics of the fracture network after mining, and it establishes the fractal permeability equation of pressure-relief gas. The results of the study show that the fracture opening shows a positive correlation with the overburden permeability, whereas the tortuosity of the fracture shows a negative correlation with the overburden permeability. The shape of the high permeability area in the fracture network is found to be similar to the hat-shaped elliptical parabolic zone. In the process of permeability evolution, the key layer structure of the overburden rock is considered as the main factor that affects the trend of change in permeability. Furthermore, based on the above research results, this study developed a targeted design of high-level boreholes in the experimental face and reversed the permeability changes around the drainage borehole. The average error between the actual measured value and the theoretically calculated value is found to be 8.11%. The theoretical model and the permeability evolution law obtained from the research results can provide valuable references and insights into further research on the pressure-relief gas flow model in the goaf.

scholarly journals An Apparent Gas Permeability Model for Real Gas Flow in Fractured Porous Media with Roughened Surfaces

Polymers ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1937
Author(s):  
Tao Wu ◽  
Qian Wang ◽  
Shifang Wang
Keyword(s):  
Porous Media ◽  
Gas Flow ◽  
Chemical Engineering ◽  
Gas Permeability ◽  
Fractal Theory ◽  
Knudsen Diffusion ◽  
Fractured Porous Media ◽  
Permeability Model ◽  
Real Gas ◽  
Apparent Gas Permeability

The investigation of gas transport in fractured porous media is essential in most petroleum and chemical engineering. In this paper, an apparent gas permeability model for real gas flow in fractured porous media is derived with adequate consideration of real gas effect, the roughness of fracture surface, and Knudsen diffusion based on the fractal theory. The fractal apparent gas permeability model is obtained to be a function of micro-structural parameters of fractured porous media, relative roughness, the pressure, the temperature, and the properties of gas. The predictions from the apparent gas permeability model based on the fractal theory match well with the published permeability model and experimental data, which verifies the rationality of the present fractal apparent gas permeability model.

scholarly journals Coupled Effects of Stress, Moisture Content and Gas Pressure on the Permeability Evolution of Coal Samples: A Case Study of the Coking Coal Resourced from Tunlan Coalmine

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1653
Author(s):  
Guofu Li ◽  
Yi Wang ◽  
Junhui Wang ◽  
Hongwei Zhang ◽  
Wenbin Shen ◽  
...  
Keyword(s):  
Moisture Content ◽  
Coalbed Methane ◽  
Gas Permeability ◽  
Axial Stress ◽  
Gas Pressure ◽  
Pressure Curve ◽  
Permeability Evolution ◽  
Confining Stress ◽  
Qinshui Basin ◽  
Gas Seepage

Deep coalbed methane (CBM) is widely distributed in China and is mainly commercially exploited in the Qinshui basin. The in situ stress and moisture content are key factors affecting the permeability of CH4-containing coal samples. Therefore, considering the coupled effects of compressing and infiltrating on the gas permeability of coal could be more accurate to reveal the CH4 gas seepage characteristics in CBM reservoirs. In this study, coal samples sourced from Tunlan coalmine were employed to conduct the triaxial loading and gas seepage tests. Several findings were concluded: (1) In this triaxial test, the effect of confining stress on the permeability of gas-containing coal samples is greater than that of axial stress. (2) The permeability versus gas pressure curve of coal presents a ‘V’ shape evolution trend, in which the minimum gas permeability was obtained at a gas pressure of 1.1MPa. (3) The gas permeability of coal samples decreased exponentially with increasing moisture content. Specifically, as the moisture content increasing from 0.18% to 3.15%, the gas permeability decreased by about 70%. These results are expected to provide a foundation for the efficient exploitation of CBM in Qinshui basin.

scholarly journals Description of Fracture Network of Hydraulic Fracturing Vertical Wells in Unconventional Reservoirs

2021 ◽  
Vol 9 ◽  
Author(s):  
Jinghua Liu ◽  
Mingjing Lu ◽  
Guanglong Sheng
Keyword(s):  
Flow Rate ◽  
Early Stage ◽  
Fractal Theory ◽  
Fracture Network ◽  
Unconventional Reservoirs ◽  
Box Dimension ◽  
Vertical Wells ◽  
Reservoir Permeability ◽  
Fractal Index ◽  
Volume Fracturing

Based on the distribution of complex fractures after volume fracturing in unconventional reservoirs, the fractal theory is used to describe the distribution of volume fracture network in unconventional reservoirs. The method for calculating the fractal parameters of the fracture network is given. The box dimension method is used to analyze a fracturing core, and the fractal dimension is calculated. The fractal index of fracture network in fracturing vertical wells are also firstly calculated by introducing an analysis method. On this basis, the conventional dual-media model and the fractal dual-media model are compared, and the distribution of reservoir permeability and porosity are analyzed. The results show that the fractal porosity/permeability can be used to describe the reservoir physical properties more accurately. At the same time, the flow rate calculating by conventional dual-media model and the fractal dual-media model were calculated and compared. The comparative analysis found that the flow rate calculated by the conventional dual-media model was relatively high in the early stage, but the flow rate was not much different in the later stage. The research results provide certain guiding significance for the description of fracture network of volume fracturing vertical well in unconventional reservoirs.

scholarly journals Experimental investigations of CO2 seepage behaviorin naturally fractured coal under hydro-thermal-mechanical conditions

2021 ◽  
Vol 25 (6 Part B) ◽  
pp. 4651-4658
Author(s):  
Teng Teng ◽  
Xiaoyan Zhu ◽  
Yu-Ming Wang ◽  
Chao-Yang Ren
Keyword(s):  
Gas Flow ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Experimental Investigations ◽  
Permeability Evolution ◽  
Coal Permeability ◽  
Naturally Fractured ◽  
Series Of Experiments ◽  
Fractured Coal ◽  
Increasing Temperature

Gas-flow in coal or rock is hypersensitive to the changes of temperature, confin?ing pressure and gas pressure. This paper implemented a series of experiments to observe the seepage behavior, especially the permeability evolution of CO2 in naturally fractured coal sample under coupled hydro-thermal-mechanical conditions. The experimental results show that coal permeability increases exponentially with the increasing gas pressure, and tends to be linear when the confining pressure is high. Coal permeability decreases exponentially with the increasing confining pressure. Coal permeability decreases with the increasing temperature generally, but it may bounce up when the temperature rises to high. The results provide reference for the projects of coal gas extraction and carbon dioxide geological sequestration.

Gas permeability evolution characteristics of limestone under different stress conditions

2022 ◽  
Vol 29 (1) ◽  
pp. 12
Author(s):  
Yin Zeng ◽  
Lu Wang ◽  
Chaofu Deng ◽  
Qiangxing Zhang ◽  
Zhide Wu ◽  
...  
Keyword(s):  
Gas Permeability ◽  
Stress Conditions ◽  
Permeability Evolution ◽  
Evolution Characteristics

The effect of anisotropic vesiculation on the porous-permeable evolution in magmatic foams

2021 ◽  
Author(s):  
Jenny Schauroth ◽  
Joshua Weaver ◽  
Jackie E. Kendrick ◽  
Anthony Lamur ◽  
Yan Lavallée
Keyword(s):  
Percolation Threshold ◽  
Gas Flow ◽  
Gas Permeability ◽  
Dominant Mode ◽  
Porous Network ◽  
Near Surface ◽  
Shape Distribution ◽  
Aspect Ratios ◽  
Anisotropic Expansion ◽  
The Impact

<p>Volcanoes can undergo rapid transitions between effusive and explosive eruptions that are often dependant on the melt’s ability to devolatilise and outgas. Eruptive products show widely contrasting permeability values for a given porosity owing to the fact that magma properties evolve over time and space, hence porosity and permeability vary depending on transport and deformation history, scale and orientation. The vesicularity that enables bubble coalescence and permeability development, termed the percolation threshold, is experimentally determined to be at ~30-80 %, depending on the microstructure of magma (i.e. bubble size and shape distribution, crystal content, dominant mode of rheological deformation during vesiculation and flow). During ascent of magma pressure decreases and the magma adapts to these new conditions by vesiculating and expanding against wall rocks. Friction between the vesicular magma and the conduit wall encourages shear, which modifies the architecture of the vesicular network. The geometrical constriction associated with conduits, dykes or fractures which host magma thus prevents or limits the isotropic growth of vesicles; we hypothesise that geometrical constraints instead lead to different ratios of isotropic to anisotropic expansion, which impacts vesicle coalescence and the onset and development of permeable gas flow in magma. We present experimental results detailing the impact of constricting geometry on the development of a permeable porous network, by combining various diameter basalt crucibles with different sized cylindrical cores of aphyric rhyolitic glass (0.12 wt.% H<sub>2</sub>O). We vesiculate the samples in a furnace at 1009 °C for different isothermal dwell increments, before cooling our sample assembly and determining porosity, strain and gas permeability. The vesiculated rhyolites host an impervious glass rind (due to near-surface bubble resorption via diffusion) surrounding a vesicular core; as such, we measure gas permeability of the assembly after cutting the upper and lower glassy rind, to expose the permeability of the internal porous network developed experimentally. The findings indicate that increasing anisotropy, caused by minimising the extent of isotropic vesiculation and maximising vesiculation under constricted conditions, lowers the porosity at which the percolation threshold occurs by ~30 %. We postulate that pure and simple shear, developed parallel to the constricting walls, increase bubble aspect ratios and enhance coalescence. This suggests magmatic foams form connected networks at lower porosities when they vesiculate in constricted conduits, dykes and fractures, thus impacting outgassing efficiency. This implies that the physico-chemical evolution of vesiculating magma may be more strongly linked to structural and rheological controls than previously anticipated, with important implications on ascending magma evolution and eruptive processes, such as degassing, outgassing and fragmentation.</p>

scholarly journals Investigation of the Flow Properties of CBM Based on Stochastic Fracture Network Modeling

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2387 ◽  
Author(s):  
Bo Zhang ◽  
Yong Li ◽  
Nicholas Fantuzzi ◽  
Yuan Zhao ◽  
Yan-Bao Liu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Gas Flow ◽  
Distribution Patterns ◽  
Element Model ◽  
Fracture Network ◽  
Gas Pressure ◽  
Computational Domain ◽  
Fracture Density ◽  
Flow Properties ◽  
Fracture Network Modeling

Coal contains a large number of fractures, whose characteristics are difficult to describe in detail, while their spatial distribution patterns may follow some macroscopic statistical laws. In this paper, several fracture geometric parameters (FGPs) were used to describe a fracture, and the coal seam was represented by a two-dimensional stochastic fracture network (SFN) which was generated and processed through a series of methods in MATLAB. Then, the processed SFN image was able to be imported into COMSOL Multiphysics and converted to a computational domain through the image function. In this way, the influences of different FGPs and their distribution patterns on the permeability of the coal seam were studied, and a finite element model to investigate gas flow properties in the coal seam was carried out. The results show that the permeability of the coal seam increased with the rising of fracture density, length, aperture, and with the decrease of the angle between the fracture orientation and the gas pressure gradient. It has also been found that large-sized fractures have a more significant contribution to coal reservoir permeability. Additionally, a numerical simulation of CBM extraction was carried out to show the potential of the proposed approach in the application of tackling practical engineering problems. According to the results, not only the connectivity of fractures but also variations of gas pressure and velocity can be displayed explicitly, which is consistent well with the actual situation.

The Study of Prediction of Agricultural Source Pollution Emissions of Ammonia Nitrogen (AN) and Chemical Oxygen Demand (COD) Based on Bionic Neural Network Algorithm

2013 ◽  
Vol 461 ◽  
pp. 544-552 ◽  
Author(s):  
Hong Peng Guo ◽  
Gan Yu Feng ◽  
Chun Xia Liu ◽  
Xiao Yi Zhang
Keyword(s):  
Neural Network ◽  
Chemical Oxygen Demand ◽  
Rapid Development ◽  
Oxygen Demand ◽  
Ammonia Nitrogen ◽  
Average Error ◽  
Research Results ◽  
Network Algorithm ◽  
Neural Network Algorithm ◽  
Pollution Emissions

Nearly 40% of Chinese water pollution comes from agricultural sources of pollution, and the annual emissions are difference. If we want to control pollution emissions effectively, we need to accurately predict the amount of agricultural emissions of Ammonia Nitrogen (AN) and Chemical Oxygen Demand (COD). Due to the complex mechanism of the agricultural non-point source pollution, its emissions are very difficult to measure. Currently, the Bionics Research is in a stage of rapid development, and it continues to expand into many new areas of research. So the comprehensive study of Bionics and pollutant control study will be a good choice. This research used bionic BP（Back Propagation） neural network algorithm, and used pollution census data from 2002 to 2007 and established neural network model with neural network algorithm. And we predicted the agricultural sources of emissions of AN and COD with the data from 2008 to 2010. Finally we compared the predicted value and the actual value. Research results showed that, with using the bionic BP neural network, agricultural sources emissions of AN and COD are evaluated actually and the results indicate that the average error is under 5.0%. Research results proved that the model is effective. The neural network is a scientific predict method for the agricultural sources emissions of AN and COD. It can be widely used in the prediction of agricultural sources emissions of AN and COD.

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