Gas Flow Resistance Research Articles

A survey study on the availability of anaesthetic breathing systems and their use in dogs weighing 5–10 kg

ObjectiveTo investigate which breathing systems are available and why they are selected in dogs weighing 5–10 kg. Study designAnonymous online voluntary open survey. MethodsAn online survey, designed following CHERRIES guidelines, was advertised through the American College of Veterinary Anesthesiologists - List, Association of Veterinary Anaesthesia and European College of Veterinary Anaesthesia and Analgesia (February–March 2022). A convenience sample was taken. ResultsOf the 256 responses received, 138 were completed. This included (n responses received) veterinarians (107) and veterinary nurses or technicians (29) actively involved in the anaesthesia of dogs.The most prevalent breathing systems available to respondents were circle (99%), coaxial Bain (79%) and modified Ayre’s T-piece (with adjustable pressure limiting valve; 72%). When recommending a dog weight range suitable for the use with these systems, respondents advised a median (interquartile range) from 5 (3–10) to 100 (100–100), 3 (0–8) to 20 (10–33) and 0 (0–0) to 10 (7–10) kg, respectively. Respondents agreed or strongly agreed that important factors in selecting a breathing system were the fresh gas flow requirement (92%), dog weight (91%), resistance (83%) and environmental pollution (79%). In clinical scenarios based on 5–10 kg dogs, the circle system was chosen by 58% for a thin and 77% for a keel-chested versus 44% for an obese and 66% for a barrel-chested dog, respectively. Conclusions and clinical relevanceThe circle system is the most commonly available breathing system. The minimum weight limit used for the circle system is less than that reported by previous surveys. Several factors influence the choice of breathing system other than dog weight.

Optimizing spiral‐wound pervaporation membrane modules through simulation: Unraveling the permeate spacer structure

AbstractFor low‐pressure pervaporation, the performance of spiral wound pervaporation membrane (SWM‐PV) module is significantly influenced by permeate spacer structure. This study addresses mass transport challenges in SWM‐PV modules, focusing on increased gas flow resistance and vacuum attenuation due to membrane envelope deformation in the permeate side channel. Employing fluid and structural simulation models to evaluate phase change and membrane deformation, we successfully optimized SWM‐PV module configurations for improved ethanol recovery. Our strategies included a mass transfer‐enhanced feed spacer to mitigate concentration polarization, a high‐strength permeate spacer to alleviate membrane deformation, and tailored membrane envelopes to balance packing density and mass transfer efficiency. These synergistic optimizations led to a 22.1% improvement in ethanol mass transfer coefficient and a 78.5% reduction in module's specific energy consumption. Our work reveals the importance of permeate spacer structure in optimizing SWM‐PV modules, offering clear guidance for the development of mass transfer‐enhanced SWM‐PV modules.

CFD investigation of post-combustion CO2 capture using an industrial spray tower: Regulation effects of spray schemes

The use of spray towers for post-combustion CO2 capture has attracted growing industrial interest. However, its practical application is hampered by a lack of knowledge about CO2 spray absorption on an industrial scale. Herein, we developed a numerical model to explore the potential of the spray tower for CO2 removal at a 330 MW coal-fired power plant. The model was developed in the Euler-Lagrange framework integrated with interphase transfer models. The variations of gas-droplet flow, CO2 removal efficiency, CO2 loading of rich solution, and temperature distribution under different spray schemes were investigated. It was found that gas flow hydrodynamics and CO2 removal performance can be regulated by the spray scheme. Compared to the conventional downward spray scheme, the lower nozzle layer adopted an upward spray scheme can improve the uniformity of the gas flow and results in several advantages: (1) average droplet residence time is extended by 5.2 %; (2) CO2 removal efficiency increases from 79.1 % to 82.9 %. This improvement is attributed to two factors: one is the droplet’s re-distribution, lowering the gas flow resistance in the region below the first spray layer near the inlet; the other is the change in gas-droplet interaction whereby the upward-moving droplets entrain the gas to flow upwards. Moreover, we investigated the effects of the spray schemes under varying flue gas loads. Under these conditions, the upward spray mode adopted in the first layer shows the best CO2 removal performance. Further theoretical analysis reveals the mechanisms underlying the regulation effect. The findings in this work will benefit the design and optimization of the industrial-scale spray tower for CO2 removal.

A permeability model for the fractal tree-like fracture network with self-affine surface roughness in shale gas reservoirs

The complex natural fracture network with self-affine rough surface and branching characteristics significantly impacts the gas transport in shale gas reservoirs. However, its effects on the permeability have not been studied so far. This study proposes an analytical permeability model for the fractal tree-like fracture network with self-affine surface roughness and branching characteristics. Firstly, the self-affine rough profiles of fracture surface are generated at different fractal dimensions by the Weierstrass–Mandelbrot function and a rough fractal tree-like fracture network is constructed with these surface profiles and branching characteristics. Then, an analytical permeability model is proposed to consider the effects of fracture surface roughness and tree-like branching characteristics on gas flow. This analytical model is verified by numerical simulations. Finally, the velocity distribution of the fracture network and the sensitivity of its structure parameters are analyzed. It is found that eddy flow is more easily formed on rougher fracture surfaces with larger fractal dimension when their fracture aperture is at millimeter scale. The eddy flow disappears when the fracture aperture is at micron scale. Bigger gas flow resistance and more energy loss are observed for smaller fracture aperture and rougher fracture surface. The gas velocity in rough fractures decreases by 60% at micron scale, but decreases by 50% at millimeter scale. Gas flow resistance also increases with the increase of branch angle, branch level and length ratio, but decreases with aperture ratio. As a result, permeability decreases with fractal dimension, branch angle, branch level and length ratio, but increases with aperture ratio.

PORE-SCALE ANALYSIS OF AQUEOUS PHASE TRAPPING RESISTANCE IN CARBONATE GAS RESERVOIRS

In carbonate gas reservoirs, water in aquifers can flow into reservoirs through highly permeable fractures, which leads to aqueous phase trapping and reduces well productivity. In this paper, flow resistances during aqueous phase trapping are analyzed. A mathematical model of aqueous phase trapping resistances is established at the pore scale, taking into account capillary pressure, gas viscous force, and water viscous force. The factors affecting aqueous phase trapping resistances are discussed, including pore radius, throat radius, flow velocity, fracture width, etc. Results show that gas flow resistance in the matrix easily exceeds the water flow resistance in fractures. Water in fractures occupies the flow path in the formation and traps gas inside the matrix. Consequently, aqueous phase trapping occurs. The gas flow resistance is mainly affected by the throat radius because the capillary pressure accounts for more than 98% of the gas phase flow resistance. When the throat radius increases from 0.1 μm to 10 μm, the gas flow resistance decreases by 89.99%. The water flow resistance is mainly influenced by the fracture width and the flow velocity. Water flow resistance has a linear relationship with the flow velocity. The water flow resistance is also sensitive to fracture width. When the fracture width rises from 0.2 μm to 1 μm, the water flow resistance diminishes by 96%.

Effect of multi-channel shape design on dynamic behavior of liquid water in PEMFC

A well-designed flow channel is crucial for effective water management in proton exchange membrane fuel cell. This study presents novel simulation investigation of the dynamic behavior of liquid water in three-dimensional multi-channels with various shape designs, including straight channel (SC), blocked channel (BC), wave channel (WC), and tapered channel (TC). The first, second, and third single channels are arranged in order from gas inlet in multi-channel. The results indicate that drainage rate of first channel in multi-channel is slower than that of second and third channel. Among the four designs, BC and TC reduced water ejection time by 7 ms and 6.5 ms respectively compared to SC, and reduced the time by 39 ms and 38.5 ms respectively compared to WC. In base case, drag reduction rate of TC compared to BC and WC increased by 4.12% and 20.98% respectively. However, WC has the smallest water coverage and average drag reduction ratio, while SC has a lower average gas flow resistance coefficient. This research offers innovative perspectives and theoretical foundations for current flow field design.

A Simplified Lattice Boltzmann Boundary Conditions for Gas Transport in Self-Affine Microchannels with an Inherent Roughness of in a Tight Reservoir

A simplified method of determining lattice Boltzmann boundary conditions based on self-affine microchannels with an inherent roughness in a tight reservoir is presented in this paper to address nonlinear efficiency problems in fluid simulation. This approach effectively combines the influence of rough surfaces in the simulation of the flow field, the description of L-fractal theory applied to rough surfaces, and a generalized lattice Boltzmann method with equivalent composite slip boundary conditions for inherent roughness. The numerical simulations of gas slippage in a two-dimensional plate model and rough surfaces to induce gas vortex reflux flow are also successfully carried out, and the results are in good agreement with the simulation results, which establishes the reliability and flexibility of the proposed simplified method of rough surfaces. The effects of relative average height and fractal dimensions of the rough surfaces under exact boundary conditions and equivalent coarsened ones are investigated from three perspectives, namely those of the average lattice velocity, the lattice velocity at average height position at the outlet, and the coefficient of variation for lattice velocity at average height position. It was found that the roughness effect on gas flow behavior was more obvious when it was associated with the enhanced rarefaction effect. In addition, the area of gas seepage was reduced, and the gas flow resistance was increased. When the fractal dimension of the wall was about 1.20, it has the greatest impact on the fluid flow law. In addition, excessive roughness of the wall surface tends to lead to vortex backflow of the gas in the region adjacent to the wall, which greatly reduces its flow velocity. For gas flow in the nanoscale seepage space, wall roughness hindered gas migration rate by 84.7%. For pores larger than 200 nm, the effects of wall roughness on gas flow are generally negligible.

Permeability damage and hydrate dissociation barrier caused by invaded fracturing fluid during hydrate reservoir stimulation

Hydraulic fracturing is a promising stimulation technology for enhancing the gas productivity and energy efficiency of low-permeability hydrate reservoirs. Presently, most studies focus on the fracturing feasibility of hydrate-bearing sediments and recovery efficiency after fracturing. Although the fracturing fluid inevitably invades the hydrate reservoirs during fracturing, the effects of invaded fracturing fluid on sediment permeability and hydrate dissociation have not been investigated yet. In this study, the invasion of water-based fracturing fluid into hydrate-bearing sediments was experimentally studied to clarify the dynamic characteristics of the fracturing fluid invasion, including its effects on sediment permeability and hydrate dissociation. The results revealed that the fracturing fluid loss rate was initially high but abruptly became extremely small, potentially because of the filter cake deposition on the fracture surface and the secondary hydrate formation in the invaded zone. However, the invaded fracturing fluid increased the dissociated gas flow resistance and inhibited the hydrate dissociation and gas production that yielded a two-stage gas production process, including slow hydrate dissociation in the invaded zone followed by relatively fast hydrate dissociation in the uninvaded zone. Furthermore, the degree of permeability damage in the invaded zone gradually decreased with the increasing invasion distance that was caused by the variations in the microscopic filtrate–sediment reactions. Interestingly, the water saturation measured by NMR gradually decreased from about 90% to 60% (initial water saturation) along the invasion distance. This phenomenon indicates that water sensitivity and water lock acted as the primary sources of permeability damage to the clayey–silty sediments after fracturing fluid invasion, suggesting that inhibiting clay swelling and increasing the flowback rate of the invaded fluid were essential for reducing permeability damage. Noted that using the fracturing fluid with breaker and KCl exhibited the lowest degree (25%) and shortest distance (<15 cm) of sediment permeability damage. The present results are vital for applying hydraulic fracturing in the field tests of hydrate reservoirs to optimize the fracturing fluid and improve the fracturing stimulation effect.

Numerical investigation of water and heat recovery from flue gas by using nanoporous ceramic membrane tubes

Direct emission of high humidity flue gas results in great wastage of water and thermal energy. Ceramic membrane technology has been widely regarded as a potential technology for water and heat recovery from flue gas. This study presents numerical investigations of water and heat recovery processes from flue gas by using nanoporous ceramic membrane tubes (CMTs). A comprehensive mathematical model is developed based on the Kelvin equation, and the Hagen–Poiseuille equation is applied to calculate the bilateral pressure difference needed for continuous recovery operation. Decreasing the pore size of the separation layer of the ceramic membrane improves the capillary condensation flux but also drastically increases the required bilateral pressure difference. CMT with a pore size of 20 nm is appreciated for the studied conditions. The performances of the CMTs located in the last rows along the flow direction are limited by local low gas temperature and humidity. Twelve rows of tubes are suggested to be arranged along the gas flow direction for ceramic membrane devices with pore sizes of 20 nm and higher. A low transverse spacing obviously improves the overall water and heat recovery efficiency of the device, decreases the performance of each tube, and enhances the gas flow resistance. A transverse spacing ratio of less than 1.4 is suitable for the studied conditions. A combined arrangement by substituting the tubes located in the last rows with those of smaller pore size is a better method than using uniform tubes. The device with combined 20 and 10 nm CMTs is suggested for the studied conditions.

Experimental study on wet gas condensation heat transfer and flow resistance in horizontal intensified tube

The heat transfer and flow resistance characteristics of in-tube vapor condensation with high content non-condensable gas is significant for designing waste heat recovery devices of gas-fired boilers. In this paper, the forced convection condensation of wet gas in the horizontal tube is experimentally investigated with a non-condensable gas mass fraction of 83–95%. The condensation heat transfer coefficient, thermal resistance and pressure drop are compared between bare tube and two intensified tubes, i.e., the corrugated and spiral tube, under various Reynolds number, wall subcooling degree and inlet humidity. The results show that the in-tube condensation heat transfer coefficient increases with increasing Reynolds number and inlet humidity, but decreases with increasing wall subcooling degree. Compared with the bare tube, the heat transfer coefficient and pressure drop increase up to 47.13% and 16.00% respectively for the spiral tube, and 116.04% and 88.48% respectively for the corrugated tube. When combing the heat transfer and flow resistance factors, the maximum comprehensive performance coefficients are 1.71 and 1.44 for corrugated tube and spiral tube respectively. The superiority of corrugated tube in the wet gas condensation is benefit from effective breaking the non-condensable gas film and promoting the vapor diffusion on the interface.

Numerical Simulation and Theoretical Analysis of Flow Resistance Characteristics in the Honeycomb Ceramic Conduit

In this study, three-dimensional numerical simulations were established for a honeycomb ceramic conduit, and the effects of the inlet methane volume fraction, inlet velocity, and the conduit length on the gas temperature and flow resistance in the conduit were investigated. The simulation results indicate that the mean gas temperature first rises rapidly and then slowly, with an increasing inlet methane volume fraction. The mean gas temperature increases slightly with an increasing inlet velocity, and first increases and then decreases with an increasing conduit length. As the inlet methane volume fraction increases, the conduit pressure loss increases, but the increase rate gradually slows down. The conduit pressure loss increases approximately linearly with an increasing inlet velocity and conduit length. A prediction model for the pressure loss in the conduit was obtained by a theoretical analysis. The theoretical results agree well with the simulation results, and the deviations between the theoretical and simulation results were in the range of 3.7% to 12.3%. When the mean gas temperature in the conduit was less than 1000 K, the deviations were less than 6.5%.

A novel 3D numerical model coupling droplet transfer and arc behaviors for underwater FCAW

Based on the VOF method (Volume of Fluid Method), a non-axisymmetric three-dimensional (3D) numerical model was developed in this paper, which coupled the droplet and arc and simulated the typical globular repelled transfer process with large droplet in the underwater wet flux-cored wire arc welding (FCAW) process. The results show that in addition to the action of gravity, surface tension and self-induced electromagnetic force, the droplet is also affected by the gas flow generated by the wire, the gas flow resistance in the bubble and the force caused by metal evaporation. The rotation of the droplet around the wire axis is mainly affected by the gas flow generated by the flux core. But the angle of the droplet deviation from the wire axis is determined by all external forces. The path of current line is changed by the droplet movement, thereby constraining the behavior of the arc. In order to verify the validity of the numerical model, images of the metal transfer are collected by a high-speed camera, and the simulated values are in good agreement with the experimental ones.

Influence of the shape on the hydraulic resistance of bypass channels inside a smart pig for low pressure gas pipeline inspection

The in-line smart pig for gas pipeline diagnostics is driven by the pumped gas and performs quality diagnostics only if its speed is constant, when the information reading is uniform along the length of the pipeline. In a low-pressure gas pipeline, if there are inhomogeneities on its walls, the condition of the pig speed constancy is easily broken, as the force of resistance to the pig movement on the stoppers is comparable with the difference of pressure forces acting on its ends. A central bypass channel of constant cross-section is usually used to control the pig velocity. The paper shows insufficiency of such method of regulation, leading to noticeable flow pulsations at the outlet of the channel. The use of variable cross-section of the bypass channel along its length in the form of a Laval nozzle to reduce flow pulsations is proposed. The numerical simulation of gas flow in Laval nozzles of different configuration is performed; it is shown that for all considered nozzles, the pressure pulsation at the channel outlet is 20-30 times less than that in the cylindrical channel, which simplifies the velocity control of such pig. However, it is not possible to completely avoid detachment of the flow from the walls of the expanding part of the nozzle, so in order to reduce the area of the detachment zone and reduce the flow resistance force, additional peripheral bypass channels connecting the inlet end of the pig with the diffuser section of the central bypass are added. Thus, a 40% reduction of gas flow resistance force through the bypass compared to the cylindrical bypass is obtained.

Effects of the Layered Distribution Pattern on the Gas Flow Resistance through the Bed with the Multisize Irregular Particle for the Waste Heat Recovery

The application of the sinter vertical cooling technology in the iron and steel industry is conducive to the realization of the double carbon in China. To reduce the energy consumption and improve the economy of the new process, the gas flow resistance in the sinter bed under the layered distribution pattern was experimentally studied. The gas flow resistance of most of the layered distribution modes is lower than that of the random distribution mode. Among all layered arrangement modes, the layered mode with the particle size increasing from the bottom-up has the lowest resistance, followed by the layered mode with the particle size decreasing from the bottom-up. These two modes ensure the feasibility of the application of the layered distribution pattern in the continuous production of the moving bed. Besides, increasing the number of layers benefits the reduction of the gas flow resistance, which has a more significant effect on the layered mode with the particle size increasing from the bottom-up. For the sinter mixture with the equivalent particle diameter of 11.45 mm, the gas resistance of the modes with the particle size increasing and decreasing from the bottom-up decreases by 11.71% and 8.26% with the layer number increasing from three to five, respectively. Also, the effect of the layered distribution pattern on the gas flow resistance progressively weakens with increasing the equivalent particle diameter. For the five-layer distribution mode with the particle size increasing from the bottom-up, the gas resistance decreases by 2.72% with the equivalent particle diameter increasing from 11.45 mm to 15.45 mm, while that decreases by 4.61% with the equivalent particle diameter increasing from 15.45 mm to 19.45 mm. What's more, the change of the equivalent particle diameter has a more significant influence on the layered mode with the particle size decreasing from the bottom-up. With the equivalent particle diameter increasing from 15.45 mm to 19.45 mm under the five-layer distribution pattern, the gas resistance of the layered mode with the particle size increasing from the bottom-up reduces by 4.61%, while that of the mode with the particle size decreasing from the bottom-up reduces by 7.38%.

Mechanistic modeling and measurement of foamed gas flow resistance in fractures

Geologic heterogeneity is one of the important factors controlling migration and distribution of nonaqueous phase liquids in the subsurface. Heterogeneity, such as fractures, complicates the effectiveness of environmental remediation, and uncharacterized aquifer heterogeneity causes significant uncertainties in the removal of nonaqueous phase liquids. Foaming an injection gas is an effective method to alleviate the challenges in accessing heterogeneous media during remediation processes because foam is nonNewtonian and redirects gas and liquid flow. Foamed gas may also assist in increasing the storage of carbon dioxide in saline formations. This paper investigates foam flow behavior in microscale fractures and develops a mechanistic transient foam flow model using the population balance method. Microscale experiments in fractures with apertures of 25 and 88 μm are used to validate the model for pressure drop, gas saturation, and bubble texture. Key differences related to modeling foam in fractures are the potential for continuously varying gas–liquid curvature in fractures and the relationship of this curvature to apparent foam viscosity. Incorporation of a local foam flow resistance factor is important to representing flow physics accurately. Hence, the results of this study provide foundational understanding for upscaling foam rheology in different sized fractures to ensure successful operations in soil/aquifer remediation and CO2 storage in saline formations.

Gas Permeability Model for Porous Materials from Underground Coal Gasification Technology

Underground coal gasification (UCG) technology converts deep coal resources into synthesis gas for use in the production of electricity, fuels and chemicals. This study provides an overview of the systematic methods of the in situ coal gasification process. Furthermore, the model of the porous structure of coal has been presented and the gas movement taking place in the carbon matrix—which is part of the bed—has been described. The experimental tests were carried out with the use of air forced through the nozzle in the form of a gas stream spreading in many directions in a porous bed under bubbling conditions. The gas flow resistance coefficient was determined as a function of the Reynolds number in relation to the diameter of the gas flow nozzle. The proprietary calculation model was compared to the models of many researchers, indicating a characteristic trend of a decrease in the gas flow resistance coefficient with an increase in Reynolds number. The novelty of the study is the determination of the permeability characteristics of char (carbonizate) in situ in relation to melted waste rock in situ, taking into account the tortuosity and gas permeability factors for an irregularly shaped solid.

Experimental study on the permeability and resistance characteristics in the packed bed with the multi-size irregular particle applied in the sinter vertical waste heat recovery technology

The gas flow resistance in the packed bed of multi-size irregular particles applied in the sinter vertical cooling process is measured experimentally to analyze the effect of the equivalent particle diameter (dp,m) and the particle size distribution on the permeability and resistance characteristics. Results show that the flow resistance per unit bed height (ΔP/L) decreases with the reduction of dp,m. However, the decrement of ΔP/L ascends first and then descends due to the comprehensive influence of the bed voidage and the particle size distribution, which is quite different from that in the mono-size sinter bed. Compared to the mono-size sinter packed bed, the bed permeability of the multi-size sinter mixture is lower under the same equivalent particle diameter. The particle size distribution of the multi-size sinter mixture has a great impact on the gas flow regime, especially at the low gas velocity. This makes the gas flow resistance in the packed bed of the multi-size sinter bigger. Since the mean error of the previous resistance correlations is greater than 44.79%, the resistance correlation applicable for the multi-size sinter is obtained by modifying the Ergun equation with the mean error less than 10%.

Permeability and thermal conductivity models of shale matrix with a bundle of tortuous fractal tree-like branching micropore networks

The complex pore structures are of great significance to gas transport and heat transfer in shale gas reservoirs, but an accurate prediction of permeability and thermal conductivity is a challenge to a porous medium with the complex geometry and distribution of pore networks. This study investigates the permeability and thermal conductivity of shale matrix with a bundle of tortuous fractal tree-like micropore networks. First, a new permeability model and a new dimensionless effective thermal conductivity model of shale matrix are developed to include the branching and tortuous characteristics of the fractal tree-like network. Then, the permeability model is validated by experimental data, and the dimensionless effective thermal conductivity model is compared with simulation results in literature. Last, sensitivity analysis is conducted to identify key parameters in these two new models. It is found that the two new models can well describe the gas transport and heat transfer in shale matrix with a bundle of tortuous fractal tree-like pore networks. The permeability model has much higher accuracy than traditional models. Tortuosity fractal dimension and radius fractal dimension of shale matrix with the bundle of tortuous fractal tree-like networks have negative influences on both permeability and thermal conductivity. Length ratio and radius ratio significantly alter the gas flow resistance and thermal resistance, and thus lead to the change of permeability and thermal conductivity. Branching angle has insignificant effect on the permeability and thermal conductivity and thus is ignorable.

Effects of Seepage on Gas Loss through Shale Desorption during Shale Core Removal

Summary In the process of shale coring, the gas adsorption will increase the flow resistance of gas inside the core, which will inevitably affect the accuracy of shale gas loss. To clarify the underlying effects of seepage flow and related factors during shale desorption, we conducted an experimental study on the influence of methane on seepage resistance of fractured shale and matrix shale under different adsorption pressures. Changes in reservoir fluid and deformation resulting from CH4 saturation adsorption resulted in changes in shale permeability. This study investigated six adsorption durations (2, 4, 6, 12, 18, and 24 hours) under adsorption pressures of 5, 9, and 13 MPa in shale samples. During each cycle, different injection pressures (2 to 6 MPa) were applied, and seepage resistance of shale samples was measured by the transient method. The results showed that the permeation resistance of the sample decreased significantly after adsorption of CH4 reached saturation and decreased with increasing CH4 adsorption duration. Compared with matrix shale samples, fractured shale samples were shown to have more suitable pore microcracks and higher CH4 affinity. Therefore, fractured samples were found to have higher permeability resistance and higher adsorption capacity compared to matrix shale. The permeability flow of a sample had a negative exponential relationship with confining pressure, and stress sensitivity increased with increasing CH4 adsorption time. The model representing gas loss indicated a positive correlation between change in impermeability and the flow of escaped gas on the core surface. A significant reduction in the impermeability of the core will result in a significant reduction in shale gas loss.

Simulation of the Extraction Efficiency of Coalbed Methane under Water Injection: A Gas-Liquid-Solid Coupling Model

Coalbed methane is always a major hidden danger that affects mining safety in coal mines. In the study of coal seam water injection to control gas disaster, the increase of free water content is helpful to destroy the integrity of coal seam and to promote the flow of gas in fractures. However, when the free water fills the fracture space, it will increase the flow resistance of gas, and then will reduce the gas extraction efficiency. At present, there is currently no mathematical model describing the effects of coal seam water injection that combines these two aspects on gas drainage. In this study, a series of experiments were conducted to study the differences in mechanical property changes under wetting conditions with different coal samples. The experimental results show that the elastic modulus and compressive strength decrease as an exponential function with increasing water pressure. Based on the experimental results, a gas-liquid-solid coupling model including effective stress change and gas desorption is established and used to predict a field gas extraction application. According to the results of the numerical model, In the plastic failure zone of coal seam, the permeability increases, the elastic modulus drops and gas migrates faster. In the water wetting zone, the free water occupies the fracture space, which blocks the gas migration channel. The overall effect of water injection on gas extraction depends on which impact plays a dominant role. The established gas drainage model is validated by field data and can reflect the pattern of borehole damage and gas drainage under water injection.