Seepage Process Research Articles

Geochemical features of altered carbonaceous mudstones from Troyanovo-3 mine borehole (Maritsa Iztok lignite field, Bulgaria)

We sampled and studied a borehole located in the southern part of Maritsa Iztok lignite field (Bulgaria) which comprises Late Miocene-Pliocene sediments of Maritsa Formation. The current report of Troyanovo-3 Mine sequence is the first to our knowledge. It represents a lignite-mudstone succession with variations in organic matter (OM) maturity. Thirty eight coal and mudstone core samples showed predictable ash and sulfur content. The XRD study showed illite/muscovite, illite/smectite, kaolinite, chlorite and quartz as main constituents that argue for a detrital origin. Additionally, we identified pyrite and gypsum and some peaks of marcasite and elemental sulfur. A set of eight mudstone samples rich in OM was selected for further geochemical analyses. The OM was classified as type III and II/III kerogen based on Rock-Eval pyrolysis data. The low amounts of extractable organic matter (0.01–2.25%) we found are consistent with the samples' low maturity and kerogen type. The yields of two samples were too low for further fractionation. Asphaltene amount (26.1–79.7%) predominates in the extracts. Diterpenoids (neutral fraction) and their polar analogues (slightly polar fraction) are highly abundant. In slightly polar fractions we registered ketotriterpenoids (mainly lupenones) in addition to the linear n-alkan-2-ones.OM elevated maturity of the deepest sample (59.60 m depth) was evidenced mainly by hopane distributions, i.e. Ts/(Tm + Ts), homohopane H31αβ index, hopane ratios (H29αβ/H30αβ) and H27β/H27α. The organic geochemistry results do not fit the ordinary regional maturity trend. OM maturity variation, superimposed over natural low coalification degree, could be ascribed to an interaction with ascending hot reductive fluids. The sulfide mineralization found in the fractures also gives indications about the fluid circulation. Another thermal alteration affecting the middle part samples (24.0–28.3 m) was suggested due to elevated Tmax values and HI and OI relation for a charcoal piece and carbonaceous mudstone. Smoldering processes affecting these samples were presumed.Low-temperature alteration processes were identified by n-alkanes, n-alkan-2-ones, and n-alcohols expulsion and downwards migration (from 18.0 m to 30.0 m) accompanied by a clear terpenoids depletion. The 17,21-seco-hopane-17,21-dione found for the first time for Maritsa Iztok Basin (MIB) samples further suggested processes of water seepage and wash-out. Microbial degradation activities usually accompanying water-washing possibly led to a specific n-alkan-2-one distribution. All the features we report point to either an even-numbered n-alkanoic acid decarboxylation or to a selective microbial degradation of odd-numbered n-alkanes to n-alkan-2-ones. In all, the history of the coal-mudstone sequence is complex, overprinted by variable alteration processes, first ever reported for MIB samples.

Effect of water on methane diffusion in coal under temperature and pressure: A LF-NMR experimental study on successive depressurization desorption

Coalbed methane production is a process of desorption, diffusion, and seepage with the successive decrease of reservoir pressure. However, desorption at atmospheric pressure has been mainly used to investigate the gas diffusion of water-bearing coal. The influence of confining pressure and gas pressure on methane diffusion is not considered in this case. So, the question is, how does the variation of the methane diffusion coefficient of water-bearing coal during desorption? How is it different from dry coal? What is the difference between the methane diffusion behavior of anthracite and bituminous coal? To address these problems, we select low-volatile anthracite in the south of Qinshui Basin and high-volatile bituminous coal in the south of Junggar Basin. The methane diffusion of water-bearing and dry coal during the successive depressurization desorption is compared by low field nuclear magnetic resonance. The influence mechanism of water on methane diffusion is explored from the pore structure, wettability, and external stress. The results show that the methane diffusion coefficient of water-bearing anthracite and bituminous coal increases with the decrease of gas pressure. The methane diffusion of water-bearing coal is affected by the combination of the increase of methane desorption volume (positive effect) and the increase of effective stress (negative effect). When the gas pressure decreases from 6 MPa to 2 MPa, the negative effect is dominant, and the effective diffusion coefficient of methane in coal is poor; When the gas pressure is less than 2 MPa, the positive effect is dominant and the effective diffusion coefficient increases significantly. The homogeneity of methane effective diffusion path of water-bearing anthracite is enhanced, resulting in higher methane desorption rate and effective diffusion coefficient than dry coal. The methane effective diffusion pore size of water-bearing bituminous coal decreases, resulting in the effective diffusion coefficient of methane less than that of dry coal. These results are of great significance to reveal the methane diffusion behavior of coalbed methane in the actual production.

Experimental research of the surfactant effect on seepage law in coal seam water injection

Coal seam water injection is one of the important means of mine disaster prevention, which helps to restrain the production of dust and reduce gas concentration. Ionic surfactant can change the capillary force of water in coal pore fissures, so as to enhance the wetting effect of coal seam water injection. However, the research on the effect of surfactant on the seepage process is still relatively weak. In order to explore the influence of surfactant on the seepage of coal seam water injection, the bituminous coal of Daliuta Coal Mine was used as the experimental coal sample to carry out wettability test and triaxial seepage experiment. The influence mechanism of capillary effect in the wetting and seepage stage of coal seam water injection is analyzed. The results show that the water injection process of cylindrical coal core goes through the unsaturated seepage stage and the steady seepage stage. In the process of unsaturated seepage, the increase rate of cumulative flow at the entrance of coal sample changes from fast to slow. And the instantaneous flow rate of surfactant is higher than that of water with a range of 0.1∼4 mL/min in the unsaturated seepage stage. The cumulative flow rate of water injection increased by 40%–60%. The instantaneous flow rate of water injection increases with the increase of capillary rising factor, and the correlation coefficients is 0.977. While in the stable seepage stage, the cumulative flow basically shows a linear increasing trend, and the increasing percentage of cumulative flow of water injection is lower than that of unsaturated seepage. It indicates that the surfactant can significantly improve the wetting rate at the stage of unsaturated seepage, and surfactants enhance the ability of liquid-solid interface to replace gas-solid interface.

Numerical Study on Seepage of Chemical Grout Flow in Rock Fracture under Temperature Field

Grouting technology is widely used to improve the mechanical properties and reduce the permeability of the rock in underground engineering. Fluidity is important to promote the grout to be injected into longer fractures, so chemical grouts with low viscosity and adjustable gel time are usually chosen to increase this property. However, the high temperature in some deep engineering leads to a faster hydration rate of the chemical grout than that in the room temperature environment, resulting in the decrease of fluidity. The heat exchange between the grout and the environment is usually ignored in the existing researches, so the aim of the numerical study is therefore to analyse the seepage process of chemical grout in the temperature field, where heat exchange between the grout and environment is considered. A sandstone model with a fracture is established in COMSOL, which is validated using laboratory experiments to confirm the accuracy of the results. The grouting time rises exponentially with the increasing of the flow distance in a single fracture, and a higher environmental temperature leads to a larger grouting time because the gap in the viscosity of the grout at different temperatures enlarges with the increasing hydration time. The effect of the temperature field on the grouting time becomes more significant when the temperature is higher and the hydration time is longer because the viscosity of the grout rises more slowly. The grouting time reduces dramatically when injection pressure is raised because an increasing pressure results in a larger aperture and less hydration time, which is one of the best ways to improve the efficiency of the grouting. The findings of this study can help for better understanding of the seepage process of chemical grout in fractures under high temperature and provide guidance for the selection of chemical grout in grouting engineering.

Research on permeable pores in collapse column fillings with different gradation structures

Particle loss is an important cause of water inrush catastrophes in collapsed columns. In order to study the relationship between the lost particles of different graded rock samples and the pore structure of the subsidence column filling, experiments were designed and the changes of the seepage parameters of graded rock samples during the particle migration process under different permeable water pressures P and axial loads F were determined. The results show that: (1) There will be obvious collapse, silting and particle loss behaviors in the sample during different loading processes, and the rock samples with gradation values of n = 0.3 and n = 0.5 are dominant; (2) The relationship between porosity φ and bearing pressure The exponential function can be used to fit the loads F well, and the porosity decreases with the increase of the bearing load. The water surging characteristics before and after 1.2 MPa are mainly in the turbulent water gushing stage, accompanied by instantaneous slurry. Possibility of splashing and indenter sliding; (3) After infiltration, the condition of the remaining skeleton rock samples in the cylinder generally shows a trend of first decreasing rapidly, then increasing slowly, and then decreasing; (4) The gradation value n of the sample and the bottom There is a good correlation between the damaged area and the mean value S of the maximum area of the top water inrush channel. The maximum area increase of the damaged area and the maximum area increase of the water inrush channel show an opposite trend. The permeable pores of the graded samples can be divided into There are three situations of digging and collapse, water inrush gap and scouring hole, and the pore seepage process can be divided into 4 stages of inoculation of water seepage, rapid adjustment, rapid scour and steady flow.

Review on the Development and Utilization of Ionic Rare Earth Ore

Rare earth, with the reputation of “industrial vitamins”, has become a strategic key metal for industrial powers with increasingly significant industrial application value. As a unique rare earth resource, ionic rare earth ore (IREO) has the outstanding advantages of complete composition, rich resource reserves, low radioactivity, and high comprehensive utilization value. IREO is the main source of medium and heavy rare earth raw materials, which are in great demand all over the world. Since the discovery of IREO, it has attracted extensive attention. Scientists in China and the around world have carried out a lot of research and practical work and achieved a series of important breakthroughs. This paper introduces the discovery process, metallogenic causes, deposit characteristics, and the prospecting research progress of IREO, so as to deepen the understanding of the global distribution of ionic rare earth resources and the prospecting direction of ionic rare earth deposits. The leaching principle of IREO, the innovation of leaching process, the influencing factors and technological development of in situ leaching process, and the technical adaptability of in situ leaching process are reviewed. The development of leachate purification and rare earth extraction technology is summarized. We aim to provide guidance for the industrial development of IREO through the above review analysis. Additionally, the problems existing in the development of IREO are pointed out from the aspects of technology, economy, and the environment. Ultimately, a series of suggestions are put forward, such as the development of ammonium free extraction technology in the whole exploitation process of in situ leaching and leachate purification and rare earth precipitation, research on enhancing of seepage and mass transfer process, and research on the development of new technologies for impurity removal of leachate and extraction of rare earth, so as to promote the development of green and efficient exploitation new technologies and sustainable development of ionic rare earth ore.

A Multi-Scale Fractal Approach for Coal Permeability Estimation via MIP and NMR Methods

Permeability in porous media has an important role in many engineering applications, which depends mainly on the pore size, distribution, and connectivity of porous media. As the pore structure distribution of coal has a multi-scale fractal dimension characteristic, this study aimed to propose a multi-scale fractal dimension characteristics units model (MFU) to describe the pore structure distribution by analyzing the multi-scale fractal dimension characteristics of coal pore media. Then, a multi-scale fractal permeability model was established based on MFU. The pore structure distribution was obtained by mercury injection porosimetry (MIP) and nuclear magnetic resonance (NMR) experiments. Based on MIP and NMR experimental data, the permeability contribution of different pore diameters were calculated. The results show that the permeability contribution of the micropore was minimal and can be ignored. The permeability contribution of mesopores was about 1–5%, and the permeability contribution of macropores was about 95–99%, which plays a decisive role in the seepage process. The calculated results, based on multi-scale fractal permeability model and the experimental permeability data, are in the same order of magnitude. The permeability prediction based on proposed model is better than classical single fractal permeability model.

Seepage Deformation and Failure of Rock Mass Under High Water Pressure With a Discrete Element Method

The seepage failure induced by high water pressure along the fault structural plane is one of the main factors for the deformation and failure of underground caverns. Based on the pipe domain seepage model with the discrete element particle flow method, the law of flow conservation is introduced, and the pressure renewal equation is improved by connecting the change of mechanical volume in timestep with the effective stress. The model for pipe domain seepage analysis of fractured rock mass is established, and the sample seepage model is used to simulate and verify the seepage process. Then, seepage failure induced by water pressure in an underground tunnel is analyzed by using this model. The results show that the improved pipe domain seepage model conforms to Darcy’s law, the seepage velocity of the model can be changed by controlling the viscosity coefficient, and the tunnel failure phenomenon is consistent with the actual phenomenon in the practical project. The research results can provide a theoretical basis and method for investigating the deformation and failure of underground caverns under complex seepage.

A multilayer soil approach for seepage process analysis in earthen levees

The analysis of seepage through earthen levees is fundamental to investigate the levee safety condition, since that the seepage phenomenon can often lead to piping causing the collapse of the levee (Saghaee et al., 2012). This work proposes a new approach for identifying the location of the saturation line through the earthen levee by using a multilayer soil approach that assumes the levee body and the levee foundation as two different layers, characterized by using a different hydraulic conductivity parameter. The main purpose is to investigate the difference in the predicted saturation line identified through the proposed method and the one based on the single layer analytical solution of the seepage flow suggested by Marchi (1961). On comparison of the saturation lines provided by two different approaches, the ratio between the river water head and the groundwater thickness or depth increases; allowing the determination of a ratio threshold above which the Marchi equation should no longer be applied. The proposed multilayer (levee and foundation) soil approach is also used to assess the seepage vulnerability of the methodology proposed by Barbetta et al. (2017). The results show that the differences between the seepage vulnerabilities evaluated using the multilayer approach and the single layer method are quite low. Although notably, significant modifications of the seepage probability are observed when the distance between the ground level and the groundwater table changes.

Selection criteria of mesh size and time step in FEM analysis of highly nonlinear unsaturated seepage process

The selection criteria of the mesh size and time step that ensures a convergent result in FEM analysis of highly nonlinear unsaturated seepage process is established. First, the concept of critical mesh size (Lc) and critical time step (Δtc) are theoretically deduced, and their framework is set up. Subsequently, formulas for the prediction of Lc and Δtc are proposed through a series of numerical experiments. Additionally, the reliability of the proposed criteria is verified by analytical solutions, model test results, and quasi-engineering problems, respectively. Finally, the ranges of Lc and Δtc under various conditions in engineering applications are recommended. The results show that the proposed criteria can predict the approximate range of Lc and Δtc, so as to obtain the convergent wetting front position and water content distribution. In addition, the criteria can be applied to the scale and dimensions of laboratory experiments and engineering cases. Moreover, the mesh size and time step were interdependent. Under limiting conditions, the appropriate mesh size should be selected prior to the time step. The research results can provide a reference for improving the accuracy of the FEM analysis of unsaturated seepage.

Seepage characteristics in loess strata subjected to single point water supply

• A Conical-like cavity was formed near the water source, and the preferential passage of water flow appeared below the cavity. • The wetting body shape gradually transformed from oblate ellipsoid to long ellipsoid after the formation of the passage. • Seepage process can be defined as four periods: rapid infiltration, stable infiltration, slow infiltration, and preferential infiltration. • A two-dimensional seepage diffusion calculation model was established and preliminarily verified by example calculations.

Interaction mechanism of water movement and gas desorption during spontaneous imbibition in gas-bearing coal

After a series of permeability enhancement and gas drainage measures are implemented in low permeability coal seams, the gas content still does not up to national standard. How to improve the transformation rate from adsorbed gas to free gas is very important. Coal seam water injection is a comprehensive disaster prevention measure. The flowing of water includes the processes of seepage and spontaneous imbibition during coal seam water injection. The process of seepage mainly displaces free gas, which shows the characteristics of rapid attenuation. The gas and water interact with each other during spontaneous imbibition which is an important way of water movement to the depth of coal seam. Spontaneous imbibition is the key to fully wetting, which provides guarantee for the water distribution in coal seam, and which establishes the foundation for the replacement of adsorbed gas. In this paper, a device integrated the isobaric water addition, isobaric desorption and spontaneous imbibition height measurement was developed. Isobaric desorption can ensure that the replaced gas is quantitatively tested. The change of electrical resistivity was grouped into the processes of sudden change, fast change and gradual change. The spontaneous imbibition height increases with increasing gas pressures during isobaric imbibition. Based on dimensionless analysis method, the mechanism that the greater the gas pressure around the capillary with one end opening, the more obvious the plugging effect is revealed. The lower the gas pressure, the better the wetting effect on the micropores and some mesopores. The equilibrium state of micropores and some mesopores determines whether the process of spontaneous imbibition is over. This study realizes the recognition of coal seam water injection technology.

Study on in situ viscosity model of tight oil and its measurement method

The change of in situ viscosity in micro-scale of tight oil reservoir has great influence on the seepage process. Due to the imperfection of in situ viscosity model and measuring method, the prediction of development effect and scientific guidance is affected. Here, an in situ viscosity model of seepage fluid in tight reservoirs is established, and the main influencing factors are studied. The in situ viscosity changes linearly with the bulk viscosity; When the average pore radius less than 500 nm, the in situ viscosity increased sharply. The approximate properties of boundary fluid and heavy oil are verified by experiments, and a method for measuring boundary fluid viscosity based on nuclear magnetic resonance (NMR) is found. According to the viscosity property of boundary fluid, the experiment is designed to verify the measurement method of boundary fluid viscosity by NMR.

On Permeability Evolution of Coal Induced by Temperature, Creep, and Matrix–Fracture Interaction

Research on the permeability evolution of coal with the influence of temperature, matrix–fracture interaction, and creep deformation has theoretical guiding significance in gas control of deep coal mines. An investigation of creep–seepage experiments and theoretical models is carried out at different temperatures. The experimental results show the decrease of permeability induced by the increase of matrix deformation during the creep process. A positive relation between temperature and matrix deformation caused by creep and thermal expansion leads to a lower permeability in the creep–seepage process. Combined with the experimental results of creep deformation and permeability evolution, a new permeability model is developed with the effect of temperature during the matrix–fracture interaction and creep process. A coupling internal swelling coefficient is adopted to characterize the matrix–fracture interaction induced by gas adsorption and thermal expansion. Moreover, the fractional derivative transient pulse method is used to calculate the experimental permeability data, and the validation of the permeability model is performed using experimental data. The proposed model can describe the experimental permeability evolution, which is consistent with the creep–seepage process.

Laboratory Studies on Permeability of Coals Using Briquettes: Understanding Underground Storage of CO2

The work presents the laboratory studies on permeability of two bituminous coal briquettes under confining pressure conditions. The research was carried out in order to assess the possibility of using bituminous coal as a sorbent for CO2 storage in underground seams. Coal permeability tests were carried out on an original apparatus for testing seepage processes under isobaric conditions on samples subjected to confining pressure. In order to determine the impact of the load on the coal briquettes’ permeability, the tests were carried out at four confining pressures: 1.5, 10, 20 and 30 MPa. The obtained results showed that the coal permeability decreases with an increase in confining pressure. At depths below 250 m, the coal can be a rock poorly permeable to CO2, and under such conditions, the applicability of technologies related to the underground storage of CO2 to coal seams is limited or even impossible.

Experimental Study on Breakage Characteristics and Energy Dissipation of the Crushed Rock Grains

Water inrush disasters are mostly related to the permeability of broken rock mass, which is associated with the deformation of rock mass, the particles migration and loss in seepage process and the breakage behavior. In this paper, samples' breakage characteristics, grain size distribution and gradation were discussed, as well as their fractal behavior and energy dissipation. It shows that compaction has an obvious effect on breakage and the fractal behavior of samples, which are inapparently affected by loading speed. The rock grains' breakage categories are related to their sharps, which affect the grain size distribution after compaction. Samples of different sizes have different optimal loading speeds and main breakage stages during compaction. It proposed two kinds of intuitive methods to judge the breakage behavior qualitatively through the grain size distribution (GSD) curves. Strain energy densities in samples mostly increase with compaction and loading speed, except for few special cases. Strain energy densities in samples are linearly correlated with the breakage index and fractal dimension, regardless of the compactions and the loading speeds. This study can provide a reference for further analysis of the permeability of the broken rock mass and even to solve the water inrush problem in the coal mines or tunnels.

Fracture evolution and nonlinear seepage characteristic of gas-bearing coal using X-ray computed tomography and the lattice Boltzmann method

Fracture is the primary channel of gas seepage in coal seams and controls the drainage efficiency of coal bed methane (CBM). However, the seepage characteristics and dynamic evolution law in the fractures of gas-bearing coal under external loads are yet to be clearly revealed. In this study, an industrial computer tomography (CT) scanner equipped with a triaxial loading system was used to conduct gas-seepage and CT scanning experiments under triaxial compression conditions. The results showed that the fracture volume and permeability decreased first and then increased during the complete stress–strain process of gas-bearing coal, displaying an approximate U-shaped variation trend involving a decrease stage, an increase stage, and a jump-increase stage. The lattice Boltzmann method (LBM) was applied to make the seepage processes of gas-bearing coal reappear, and a modified nonlinear permeability model was developed to represent non-Darcy seepage inside fractured coal. The LBM simulation results mirrored the dynamic evolution of the gas seepage field and gas permeability controlled by fracture propagation. The proposed modified nonlinear permeability model effectively reflected the nonlinear variation behaviour of gas permeability and was superior to the traditional Darcy's model in describing nonlinear seepage of gas-bearing coal.

A gas migration law study of a large-scale 3D physical similarity simulation with an adaptive Kalman filter algorithm

PurposeIn this study, a physical similarity simulation plays a significant role in the study of crack evolution and the gas migration mechanism. A sensor is deployed inside a comparable artificial rock formation to assure the accuracy of the experiment results. During the building of the simulated rock formation, a huge volume of acidic gas is released, causing numerous sensor measurement mistakes. Additionally, the gas concentration estimation approach is subject to uncertainty because of the complex rock formation environment. As a result, the purpose of this study is to introduce an adaptive Kalman filter approach to reduce observation noise, increase the accuracy of the gas concentration estimation model and, finally, determine the gas migration law.Design/methodology/approachFirst, based on the process of gas floatation-diffusion and seepage, the gas migration model is established according to Fick’s second law, and a simplified modeling method using diffusion flux instead of gas concentration is presented. Second, an adaptive Kalman filter algorithm is introduced to establish a gas concentration estimation model, taking into account the model uncertainty and the unknown measurement noise. Finally, according to a large-scale physical similarity simulation platform, a thorough experiment about gas migration is carried out to extract gas concentration variation data with certain ventilation techniques and to create a gas chart of the time-changing trend.FindingsThis approach is used to determine the changing process of gas distribution for a certain ventilation mode. The results match the rock fissure distribution condition derived from the microseismic monitoring data, proving the effectiveness of the approach.Originality/valueFor the first time in large-scale three-dimensional physical similarity simulations, the adaptive Kalman filter data processing method based on the inverse Wishart probability density function is used to solve the problem of an inaccurate process and measurement noise, laying the groundwork for studying the gas migration law and determining the gas migration mechanism.

The Seepage‐Destruction Mechanism of Water Inrush Channel of Sandstone Fault Filling Using the EDEM‐Fluent Method

By the EDEM‐Fluent coupling calculation method, the formation mechanism of the seepage failure water inrush channel and the migration of particles in the sandstone fault filling body are studied. Under the condition of variable hydraulic gradient, the whole seepage process can be divided into three stages: slow seepage stage, sudden seepage stage, and stable seepage stage. In the stage of slow seepage, the mass of lost particles is small. In the stage of sudden seepage, particles are lost on a large scale. In the stable seepage stage, the model is basically in a stable state. During the seepage process, the particles in the outlet zone will move before the particles in the inlet zone under the action of the seepage force. The overall movement trend of particles can be predicted, while the movement trajectory of a single particle is irregular. The change trend of the contact quantity between particles is basically consistent with the change in the quality of the lost particles. Moreover, the change in the contact quantity of particles is caused by the loss of the filler particles.

Numerical Analysis of Time Fractional-Order Unsaturated Flow and Its Application

Numerical simulation of unsaturated flow process is of great significance to many fields such as soil slope stability analysis and migration simulation of underground pollutants. Generally, it is widely used due to the universal applicability of Richards equation, but the seepage process described by Richards equation does not consider the anomalous diffusion phenomenon in natural environment and experiments. In response to this problem, this paper combines the Caputo derivative to obtain the time fractional Richards equation with broader seepage significance. Then the finite difference method is used to obtain the discretization scheme and the Picard method is used to solve it iteratively, and the sensitivity analysis of the fractional parameters and soil-water characteristic curves is carried out. Finally, combined with the experimental data of soil column infiltration, the numerical solutions obtained by the time fractional Richards equation under different soil-water characteristic curves are compared. The results show that the time fractional Richards equation of the VGM model has a better fitting effect with the measured data and can better describe the seepage process of groundwater in unsaturated soil.