Gas Permeability Coefficients Research Articles

Cryogenic mechanical performance and gas-barrier property of epoxy resins modified with multi-walled carbon nanotubes

Type V linerless hydrogen storage vessels made of all-composite face the challenges of cryogenic mechanical failure and hydrogen leakage of composites. The cryogenic mechanical performance and gas-barrier property of the carbon fiber reinforced polymer for Type V vessels are largely determined by the epoxy matrix. Carbon nanotubes are widely used as polymer reinforcement material to enhance the cryogenic mechanical performance and gas-barrier property of epoxy resins. In this work, multi-walled carbon nanotubes (MWCNTs) were dispersed into epoxy resins to prepare MWCNTs-modified epoxy resins. The cryogenic mechanical performance, gas-barrier and thermal properties of the modified resin were then investigated. The experimental findings revealed a 34.34% reduction in the gas permeability coefficient for the nanocomposites containing 0.9 wt% MWCNTs compared with the epoxy matrix. The tensile strength and failure strain at cryogenic temperature (77 K) experienced enhancements of 26.99% and 41.53%, respectively. In addition, the thermal stability and glass transition temperature of the modified resin were improved. As a result, the MWCNTs-modified epoxy resin exhibits improved gas-barrier property in addition to excellent cryogenic mechanical performance, making it ideal for manufacturing Type V linerless hydrogen storage vessels.

Preparation of modified atmosphere and moisture packaging membranes by blending quaternized polyether ether ketone with polyvinylidene fluoride and its application in grape packaging

The modified atmosphere and moisture packaging membranes for preserving Vitis vinifera L. (V. vinifera) were developed by blending triethylamine-grafted quaternized polyether ether ketone (QPEEK) and polyvinylidene fluoride (PVDF) using thermally induced phase separation. With the addition of QPEEK, the blend membranes exhibited increased hydrophilicity, gas transmission rate, and gas permeability coefficient. For the 5 % QPEEK/PVDF membrane, the water vapor transmission rate is 48.4 g/(m²·24 h), the water contact angle is 82.2°, and the CO2/O2 separation coefficient is 2.06. Compared to other groups, this membrane exhibits better tensile, swelling, and relaxation properties. These properties facilitate achieving dynamic air equilibrium within 3 days, maintaining a suitable atmosphere inside the package (3.4–4.1 % CO2 and 16.1–18.1 % O2), and timely removing moisture to prevent water vapor condensation, thus extending the shelf life of grapes to more than 25 days. Grapes packaged in 5 % QPEEK/PVDF membrane box maintained 99.3 % mass, 85.1 % firmness, and 72.2 % total phenol content, and exhibited minimal changes in soluble solids, relative electrical conductivity, and water state and distribution compared to fresh grapes. These experimental results suggest significant potential for the use of QPEEK/PVDF membranes in fruit and vegetable packaging.

Study on gas transport characteristics of manufactured sand concrete and modeling of random hierarchical bundle based on pore structure

Overexploitation of natural sand has caused severe damage to the environment, and manufactured sand to replace natural sand has become an inevitable trend in construction projects. Anti-gas permeability performance is an important index characterizing the durability of concrete, and its performance directly affects the service life and quality of concrete structures. This study evaluates the feasibility of applying manufactured sand to concrete based on its mechanical properties. In addition, we systematically investigated the influence of the properties of manufactured sand on the pore structure and gas permeability resistance of concrete with different strength grades. Furthermore, we established a random hierarchical bundle model based on the nuclear magnetic resonance(NMR) and predicted the gas permeability coefficient by simulating the pore structure distribution of concrete. The following test results were derived: First, at the same strength grade, the late compressive strength of limestone (LMS) and granite manufactured sand (GMS) concrete is higher than that of natural river sand (NRS) concrete. Therefore, choosing manufactured sand as a fine aggregate to formulate concrete in practical engineering applications is feasible. Secondly, by comparing the gas permeability resistance of concrete with different fine aggregate mechanism sands, it was found that small aggregate particles can significantly improve the gas permeability resistance of concrete. Finally, the pore structure significantly affects the anti-gas permeability property of manufactured sand concrete, in which the pore content in the range of 10–100 nm is the main factor affecting the gas permeability coefficient. Moreover, the NMR-based stochastic layered beam model predicts the gas permeability resistance of concrete with a maximum deviation of up to 30.89 %.

Poly(4-methyl-1-pentene)/ polypropylene alloy hollow fiber membrane with high rigidity for blood oxygenation

The oxygenator with hollow fiber membranes (HFMs) is the key component of the extracorporeal membrane oxygenation which allows the blood to be oxygenated and the carbon dioxide to be removed. The poly(4-methyl-1-pentene) (PMP) is recognized as the optimal oxygenated membrane material with high gas permeability coefficient, and the oxygenated membrane fabricated from it has an asymmetric structure that can resist plasma leakage for a long period of time. However, the relatively low rigidity of PMP oxygenated membrane makes it difficult to be processed in subsequent weaving and applications, during which deformation and fracture of HFMs often happen. In this work, the polymer alloy oxygenated membranes are fabricated by blending polypropylene (PP) as a high rigidity reinforcement agent with PMP via thermally induced phase separation (TIPS). Firstly, the effect of the PP content on phase separation structure and crystallization of alloy flat sheet membrane are investigated. When the PP content is 15 wt%, the rigidity of the alloy membrane reinforces dramatically. The elastic modulus and tensile strength of the PMP-PP-15 alloy membrane is 288.5 ± 12.4 MPa and 8.3 ± 0.4 MPa, respectively, which is 275.7 % and 96.7 % higher than that of the PMP membrane. Furthermore, PMP-PP-15 alloy HFM are fabricated under the optimum polymer composition. The elastic modulus of the PMP-PP-15 alloy HFM is 312.6 ± 16.0 MPa, which is 679.6 % higher than that of the PMP HFM and 40.1 % higher than that of the commercial PMP HFM. Meanwhile, the tensile strength and fracture stress are 15.4 ± 0.7 MPa and 186 ± 12.2 cN, respectively, which are both higher than those of the PMP and commercial PMP HFM. In addition, the PMP-PP-15 alloy HFM shows high gas permeability and oxygenation performance. This study might provide a convenient method to achieve rigidity reinforcement of PMP-based oxygenated membranes with great potential for application.

Transport Behavior of Pure and Mixed Gas through Thermoplastic-Lined Pipes Materials

Abstract To determine the permeability properties of lining materials for the design of nonmetallic pipes in oil and gas fields, we conducted a study on the transport behavior of pure and mixed gases (carbon dioxide [CO2] / methane [CH4]) through commonly used thermoplastic-lined pipe materials. The material tested were high-density polyethylene (HDPE), polyamide (PA), and polyvinylidene fluoride (PVDF). It was observed that the permeability coefficient of the pure gas through HDPE, PA12, and PVDF increased with increasing temperature. The permeation of mixed gas with different volume fractions was also tested at different temperatures, in which the deviation between the test and the ideal state was founded. For HDPE and PVDF, the permeability coefficient of the mixed gas is higher than that of pure gas because of the plasticization effect of CO2. However, for PA12, the permeability coefficient of mixed gas is lower than that of the pure gas. This is because of the tight interaction between the chains and the competition between CO2 and CH4 for a limited number of active sites.

Theoretical analysis and engineering application of controllable shock wave technology for enhancing coalbed methane in soft and low-permeability coal seams

Coalbed methane (CBM) is a significant factor in triggering coal and gas outburst disaster, while also serving as a clean fuel. With the increasing depth of mining operations, coal seams that exhibit high levels of gas content and low permeability have become increasingly prevalent. While controllable shockwave (CSW) technology has proven effective in enhancing CBM in laboratory settings, there is a lack of reports on its field applications in soft and low-permeability coal seams. This study establishes the governing equations for stress waves induced by CSW. Laplace numerical inversion was employed to analyse the dynamic response of the coal seam during CSW antireflection. Additionally, quantitative calculations were performed for the crushed zone, fracture zone, and effective CSW influence range, which guided the selection of field test parameters. The results of the field test unveiled a substantial improvement in the gas permeability coefficient, the average rate of pure methane flowrate, and the mean gas flowrate within a 10 m radius of the antireflection borehole. These enhancements were notable, showing increases of 3 times, 13.72 times, and 11.48 times, respectively. Furthermore, the field test performed on the CSW antireflection gas extraction hole cluster demonstrated a noticeable improvement in CBM extraction. After antireflection, the maximum peak gas concentration and maximum peak pure methane flow reached 71.2% and 2.59 m3/min, respectively. These findings will offer valuable guidance for the application of CSW antireflection technology in soft and low-permeability coal seams.

The synergistic mechanism of hydration regulation and carbonation curing on the carbon sequestration and impermeability enhancement of cementitious materials

Carbonation curing, as a novel curing method, gradually plays an important role in the reduction of carbon emissions and the improvement of durability for cementitious materials. This study considers the intervention of carbonation at different ages of hydration and investigates the synergistic effect of nano-titanium dioxide (NT) regulating cement hydration and 20% CO2 carbonation curing on the enhancement of carbon sequestration and durability performance of cement mortar. The results show that early-age carbonation curing and the addition of NT increase the unit area carbon sequestration of cement mortar at the age of 28 days by 242.75% (0.41 kg/m2); meanwhile, some micro-nano-sized calcite crystals and NT jointly play a nucleation and filling role during hydration, optimizing the pore structure. As a result, the unit area capillary water absorption coefficient and gas permeability coefficient decrease by 70.55% and 91.89%, respectively, inhibiting the continuous diffusion of CO2 and achieving controlled surface carbonation. Based on the pore characteristics of the carbonated surface, this study also proposes a “Sieve filter” structure hypothesis model, which suggests a negative correlation between pore structure and surface depth under the synergistic mechanism. This can provide innovative ideas for the cement industry to enhance the durability performance of reinforced concrete prefabricated components using carbon sequestration technology.

A semi-rigid co-poly(imide) derived from an isomeric mixture of monomers. Assessing gas transport properties in self-standing polymer membrane

Chemical structure and morphology of polymers are directly related with the membrane separation performance. Poly(imide)s (PIs) are the most widely used polymers in the preparation of membranes for gas separation applications; thus, research on the structural design of polymers is of great interest to develop new membranes. In the present work, we reported the synthesis, characterization, and measurement of the gas transport properties of a new co-poly(imide)s (PI-D2a-D2b-6FDA) prepared from a mixture of isomeric diamines. The co-poly(imide) synthetic route involved several steps, starting by a bromination reaction, followed by a double nucleophilic aromatic substitution giving an isomeric mixture of precursors, which suffered a Suzuki-Miyaura C–C cross-coupling reaction followed by the reduction of nitro groups to give two new isomeric diamines. Finally, diamines simultaneously reacted with the dianhydride 6FDA to obtain PI-D2a-D2b-6FDA. The co-poly(imide) had a Mn of 47.7 kDa and a Mw of 74.0 kDa with a PDI of 1.6. The sample exhibited a 10% weight loss at 540 °C, Tg of 280 °C, BET surface area of 110 m2 g−1, and wide-angle X-ray diffraction (WAXD) interchain d-spacing at 9.5 Å and 6.3 Å. Tensile strength, elongation at break and Young's modulus were 109.6 MPa, 6.66% and 2.18 GPa, respectively. co-Poly(imide) was soluble in various polar aprotic organic solvents such as DMSO, NMP, DMF, DMAc, THF, and chloroform, forming a self-standing dense film whose gas transport properties were measured. Pure gas permeability coefficients for H2, CO2, O2, N2, and CH4, were 47.28, 24.04, 4.35, 1.02, and 0.76 (Barrer), respectively, which follows a decreasing order by the increasing kinetic diameters of the respective gases. Ideal gas selectivities H2/N2, O2/N2, CO2/CH4, and CO2/N2 were 46.4, 4.3, 31.6, and 23.6, respectively. These gas transport properties were compared with the commercial polymer Matrimid®, showing higher gas permeability coefficients than Matrimid®.

Synthesis and gas transport properties of polynaphthoylenebenzimidazoles with keto- and sulfonic bridging groups

Polynaphthoylenebenzimidazoles (PNBI) with keto-(PNBI-CO) and sulfonic (PNBI-SO2) bridge groups were obtained by solid-state polycyclization of polyaminoimides (PANI) synthesized by polycondensation of 1,4,5,8-naphthalenetetracarboxylic acid dianhydride with 3,3`,4,4`-tetraaminobenzophenone and 3,3`,4,4`-tetraaminodiphenylsulfone in N-methylpyrrolidone, respectively. The polycondensation process and resulting chemical structure of PANI and PNBI were controlled by 1H NMR, 13C NMR and IR spectroscopy. It is shown that the temperature of solid-state polycyclization change makes it possible to obtain polymers of several of cyclization degrees. The experimental values of the gas permeability and diffusion coefficients for He, H2, N2, O2, CO2, CH4 were obtained. The gas solubility coefficients and the ideal selectivity for various gas pairs were calculated. It has been established that, in terms of the permeability-selectivity ratio, completely cyclized PNBIs occupy a more favorable position compared to incompletely cyclized ones. This result is important for polymer and a method selection to develop a selective layer of new composite membranes. The gas transport characteristics achieved for competely cyclized PNBI-SO2, as well as the film-forming properties, along with the very high thermal stability of polymers of this polymer class, are interest of further expanding the range of PNBI obtained, as well as the prospects for such new polymers using of in various gas separation processes.

Study on the permeability behaviour of hydrogen doped natural gas in polyethylene pipeline

The use of non-metallic PE pipes to transport hydrogen energy can avoid the problem of hydrogen embrittlement in metal pipes, but due to material characteristics, PE pipes exhibit gas leakage behavior. Therefore, this article conducted a study on the permeability of polyethylene (PE100) as a gas pipeline material for hydrogen-doped gas, mainly analyzing the effects of hydrogen content and gas pressure on the permeability of PE100 gas. We ensure that the raw materials are uniform and free from pore defects through microstructure observation and industrial CT characterization. The experimental results show that with the increase of hydrogen content in the hydrogen-doped gas, the gas permeability coefficient of the sample significantly increases. When the hydrogen content is 60%, the gas permeability coefficient increases by 83% compared to when no hydrogen is added. Further increase in hydrogen content results in no significant change in the gas permeability coefficient; As the gas pressure increases, the gas permeability coefficient of the s ample gradually decreases. This study will provide data support for the safe transportation of hydrogen energy and promote the development of the hydrogen energy industry.

Effect of Amino-Functionalized Polyhedral Oligomeric Silsesquioxanes on Structure-Property Relationships of Thermostable Hybrid Cyanate Ester Resin Based Nanocomposites.

Nanocomposites of cyanate ester resin (CER) filled with three different reactive amino-functionalized polyhedral oligomeric silsesquioxane (POSS) were synthesized and characterized. The addition of a small quantity (0.1 wt.%) of amino-POSS chemically grafted to the CER network led to the increasing thermal stability of the CER matrix by 12-15 °C, depending on the type of amino-POSS. A significant increase of the glass transition temperature, Tg (DSC data), and the temperature of α relaxation, Tα (DMTA data), by 45-55 °C of the CER matrix with loading of nanofillers was evidenced. CER/POSS films exhibited a higher storage modulus than that of neat CER in the temperature range investigated. It was evidenced that CER/aminopropylisobutyl (APIB)-POSS, CER/N-phenylaminopropyl (NPAP)-POSS, and CER/aminoethyl aminopropylisobutyl (AEAPIB)-POSS nanocomposites induced a more homogenous α relaxation phenomenon with higher Tα values and an enhanced nanocomposite elastic behavior. The value of the storage modulus, E', at 25 °C increased from 2.72 GPa for the pure CER matrix to 2.99-3.24 GPa for the nanocomposites with amino-functionalized POSS nanoparticles. Furthermore, CER/amino-POSS nanocomposites possessed a higher specific surface area, gas permeability (CO2, He), and diffusion coefficients (CO2) values than those for neat CER, due to an increasing free volume of the nanocomposites studied that is very important for their gas transport properties. Permeability grew by about 2 (He) and 3.5-4 times (CO2), respectively, and the diffusion coefficient of CO2 increased approximately twice for CER/amino-POSS nanocomposites in comparison with the neat CER network. The efficiency of amino-functionalized POSS in improving the thermal and transport properties of the CER/amino-POSS nanocomposites increased in a raw of reactive POSS containing one primary (APIB-POSS) < eight secondary (NPAP-POSS) < one secondary and one primary (AEAPIB-POSS) amino groups. APIB-POSS had the least strongly pronounced effect, since it could form covalent bonds with the CER network only by a reaction of one -NH2 group, while AEAPIB-POSS displayed the most highly marked effect, since it could easily be incorporated into the CER network via a reaction of -NH2 and -NH- groups with -O-C≡N groups from CER.

Effects of calcium sulfate whiskers and basalt fiber on gas permeability and microstructure of concrete

This paper aims to investigate the influence of introducing calcium sulfate whiskers (CSW) and basalt fiber (BF) on the gas permeability coefficients of concrete. Employing the Cembureau method, the research quantifies gas permeability while utilizing Nuclear Magnetic Resonance (NMR) to precisely measure pore structure parameters. The results highlight that the incorporation of CSW leads to a substantial reduction in gas permeability, exhibiting a remarkable 57.6% decrease when utilized at a dosage of 3.0 kg/m³ compared to the standard concrete. In contrast, the introduction of BF at the same dosage does not yield a commensurate reduction in permeability. Notably, the combined application of CSW and BF at 3.0 kg/m³ each yields the most effective mitigation of gas permeability. Furthermore, the judicious addition of either CSW or BF demonstrates the capacity to diminish the overall porosity of concrete, alongside a reduction in the proportion of harmful pores (R100, featuring diameters larger than 100 nm). Optimal outcomes manifest when both CSW and BF are introduced at the 3.0 kg/m³ dosage, effectively minimizing R100 and the gas permeability coefficient. It is interesting to find that in comparison to the correlation observed between the total porosity and gas permeability of concrete, the relationship between the proportion of R100 and gas permeability emerges as more statistically significant (R2 approximately 0.800), especially for CSW concrete. This can reveal the interconnection between the concrete's pore structure and its gas permeability characteristics more appropriately.

Study and application of a continuous inversion model of coal seam gas pressure in front area of heading face

The gas pressure in front area of heading face is essential to dynamically evaluate coal and gas outburst during coal mining. In this work, a novel inversion model of gas pressure in front area of the heading face was established on premise of the hypothesis that a time-dependent zone of steady flow exists within newly exposed face. The key parameters in the inversion model were obtained based on the gas emission models and field data of gas emission rate in different times, which were used to calculate the volumes of gas emission from different sources. The results show that the percentage of gas emission from the heading face, coal wall and collapsed coal ranges from 7% to 47%, 47% to 82% and 2% to 11%, respectively. Based on the calculated volumes of gas emission and gas pressure inversion model, the gas pressure was obtained and transformed to the gas content. The absolute errors between the gas content tested and transformed in every hour is 0.4%–33%, which proved the rationality of gas pressure inversion model. Furthermore, the daily drifting footage, the radius of gas pressure boundary and the gas permeability coefficient of coal seam were confirmed to have a great effect on the result of gas pressure inversion. The inversion results verify that the speedy excavation can increase the risk of coal and gas outburst. This work produces a useful method for gas disaster prevention and control that converts the gas emission rate to an index of gas pressure within coal seam.

An improved Klinkenberg permeability model for tight reservoir cores: Effects of non-linear gas slippage to real gases

Absolute permeability is one of the most fundamental reservoir-rock properties required for reservoir simulation models. Most research studies are focused on the Klinkenberg gas slippage, considering the ideal behavior of the flowing gas under first- and second-order slippage conditions. This paper assesses the non-linear slippage of real gas through the low permeability reservoir rock samples. The cubic equation of state (van der Waals/Soave-Redlich-Kwong/Peng-Robinson), coupled with Taylor series-based non-linear slippage, predicts the apparent permeability for the non-Darcy gas flow in tight reservoir rock. The novelty of the present contribution is to develop a comprehensive mathematical model to describe the temperature- and pressure-dependent non-linear slippage effect accounting for the real gas behavior, which is based on the fundamental principle of momentum balance. The thirty-nine sets of experimental results of different authors using different core samples (e.g., coal seams, tight sandstones, tight carbonates, gas-shale reservoirs) and gases (Air, H2, He, N2, CH4, C2H6, and CO2) are used to authenticate the proposed non-linear slip model for real gases. Results show that (a) the proposed model correctly predicts infinite permeability and non-linear slippage coefficients of eight-tests non-ideal gases with an average absolute deviation of ≤9.69%, (b) non-linear slippage dominates for the core samples having permeability <1.5 mD, and (c) the first- and second-order slippage coefficients vary from 0.76 to 6.22 atm and 0.15–9.30 atm2, respectively. The proposed model is simple and may readily be applied for the reservoir simulation of coal seams, tight sandstones, tight carbonates, gas-shale reservoirs, etc., for reservoir characterization, forecasting future natural gas production, decision-making, and efficient reservoir management practices for enhanced production efficiency and sustainability.

Influence of pore structure characteristics on the gas permeability of concrete

The permeability of concrete is a key factor in determining its durability. Permeability of porous materials in general is determined by pore characteristics (e.g., porosity, pore size distribution, tortuosity, etc.). In this investigation, we attempted to observe the relationship between the pore characteristics and the permeability of concrete. Nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), nitrogen adsorption, and X-ray computed tomography (X-CT) were used to examine the microstructures of three concrete materials labeled C30, C45, and C50. The results show that the combined aperture size distribution curve generated by N2GA and MIP can more accurately depict the distribution of micro to macro pores in the sample than any single method alone. The three-dimensional visualization model reconstructed by X-CT can provide a more intuitive reflection of the distribution of large pores in concrete. The pore ratios measured by NMR and MIP both have satisfactory correlations with gas permeability, but the pore ratio measured by NMR has a stronger correlation with gas permeability. There is a good correlation between gas permeability and the pore ratios contributed by different segments measured by NMR. In addition, the inherent gas permeability coefficient has a slightly stronger correlation with the median pore size than with the critical pore size.

Influences of titanium dioxide nanoparticles on regulation of crystalline growth and early carbonation of cementitious composites

As the major source of carbon emission in the construction industry, Cement has presented an urgent challenge that demands the resolution of its high carbon emission issue. Utilizing in-situ CO2 capture from plant sites for the carbonation curing of cementitious materials can be regarded as an effective carbon sequestration method. This study employs low-concentration CO2 curing to modify nano titanium dioxide (NT)-enhanced cementitious materials. By investigating the influence of highly homogeneous NT on the crystalline growth and microstructural evolution of hydration product Ca(OH)2, this research further explores the impact of low-concentration CO2 curing on the early-stage carbonation behavior of the surface layer of cementitious materials. The results of this study indicate incorporation of 2 wt% NT promotes the degree of cement hydration, particularly during the first three days, leading to a 31.11% increase in the generation of the hydration product Ca(OH)2 at 1 day and 20.82% increase at 3 days compared to the blank sample, and a significant reducing of the crystalline size and directional growth index of Ca(OH)2 to increase the specific surface area of Ca(OH)2, thereby promote early carbonation of the cementitious mortar surface. The carbon uptake of the specimens at 28 days reaches 0.94 kg/m2 after exposure to 3% CO2 concentrations, forming a dense protective layer of calcium carbonate on the surface. The gas permeability coefficient of the surface decreases by 79.57%, enhancing the resistance of long-term continuous carbonation. This study provides innovative ideas for the cement industry in terms of utilizing surface carbonation of the substrate to promote carbon sequestration technology.

Absolute Gas Permeability Coefficient of Samples with Embedded Glass Capillaries: Comparison of Measurement Results and Theoretical Calculations

Absolute Gas Permeability Coefficient of Samples with Embedded Glass Capillaries: Comparison of Measurement Results and Theoretical Calculations

Roots of Cynodon dactylon increase gas permeability and gas diffusion coefficient of highly compacted soils

Roots of Cynodon dactylon increase gas permeability and gas diffusion coefficient of highly compacted soils

Stress and permeability evolution of high-gassy coal seams for repeated mining

Coal bed methane reservoirs in China are generally characterized by high stress and low gas permeability coefficient. Protected layer mining has the effect of unloading pressure and increasing gas permeability coefficient. There are few studies in the case of repeated mining with an orthogonal arrangement of the protected layer. Based on the engineering practice of the high gas coal seams group in Xinjing coal mine, a combination of numerical simulation and field test was used. The distribution law of plastic zone, stress-strain and gas permeability coefficient of the protected layer under the two states of single mining and repeated mining were obtained. The stress and gas permeability coefficient distribution of the protected layer was divided into 5 and 6 zones in plane for single and repeated mining cases. The field test tested the distribution law of stress, gas pressure, deformation, and gas permeability coefficient, and verified the reliability of the numerical simulation results. According to the characteristics of gas permeability coefficient distribution under the condition of repeated mining, a method for accurate gas extraction is proposed. The results of the study have important implications for the design of gas extraction schemes in orthogonal repeated mining situations.

A new coal seam seepage parameter prediction method based on gas pressure recovery curve for adjacent aquifer environment

Gas extraction is the primary approach for safe and efficient coal mining, its final effect depending on the coal seam seepage parameters (coal seam gas pressure and permeability coefficient), which generally reflect the possibility and intensity of gas protrusion. However, this method is limited by the high requirement for measurement of conditions, long duration, and large errors under complicated conditions (e.g., adjacent aquifers). Therefore, this study proposed a new method to accurately obtain the coal seam gas pressure in an adjacent aquifer and introduced an advanced tool for the rapid measurement of coal seepage parameters, which were verified by engineering. Results of the mercury intrusion porosimetry demonstrated that the effective pore percentage of the coal samples was approximately 32.67%, inducing a locally high gas pressure prone zone in the test area. The multi-physical parameter test showed substantial differences in the coal sample properties, pressure distribution, and seepage parameters in the eastern and western regions of the test site. The field engineering verification results of the prediction of gas pressure, showed that the pressure recovery curve method differed from the conventional method by 4–9.6%, but the time required was only 10–50% of the latter. In the prediction of the permeability coefficient, the pressure recovery curve method had an error between 24.63 and 43.32%, and this difference was consistent with the current method when classifying the extraction difficulty. These findings are significant for the determination of gas seepage parameters at coal mines.