• Tunnel and Underground Space
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• v.31 no.1
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• pp.41-51
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• 2021

The hydraulic fracturing developed to improve permeability of tight reservoir is one of key stimulation technologies for developing unconventional resources such as shale gas and deep geothermal energy. The experimental study was conducted to improve disadvantage of hydraulic fracturing which has simple fracture pattern and poor fracturing efficiency. The fracturing experiments was conducted for tight rock using various fracturing fluids, water, N2, and CO2 and the created fracture pattern and fracturing efficiency was analyzed depending on fracturing fluids. The borehole pressure increased rapidly and then made fractures for hydraulic fracturing with constant injection rate, however, gas fracturing shows slowly increased pressure and less fracture pressure. The 3D tomography technic was used to generate images of induced fracture using hydraulic and gas fracturing. The stimulated reservoir volume (SRV) was estimated increment of 5.71% (water), 12.72% (N2), and 43.82% (CO2) respectively compared to initial pore volume. In addition, permeability measurement was carried out before and after fracturing experiments and the enhanced permeability by gas fracturing showed higher than hydraulic fracturing. The fracture conductivity was measured by increasing confining stress to consider newly creating fracture and closing induced fracture right after fracturing. When the confining stress was increased from 2MPa to 10MPa, the initial permeability was decreased by 89% (N2) and 50% (CO2) respectively. This study shows that the gas fracturing makes more permeability enhancement and less reduction of induced fracture conductivity than hydraulic fracturing.

• Composites Research
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• v.18 no.1
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• pp.10-15
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• 2005

It is useful to detect defects of a preform for resin transfer molding before and after placement into the mold. To conduct this test, the gas flow method has been developed. This method not only measures permeability but also detects defects utilizing the pressure readings obtained from the gas flow test. This paper introduces the methodology and examine the applicability to actual processes.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1396-1399
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• 2005

Gas permeability of the solidified sewage sludge needs to be characterized in order to use as a large-scale landfill cover material. Four different types of the samples were prepared for gas permeability experiments: (1) granite soil, (2) dried sewage sludge, (3) solidified sewage mixed with slag and (4) solidified sewage mixed with granite soils. The experimental instrumentation and measurement devices were newly designed and created to effectively evaluate gas permeability of the samples.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1162-1165
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• 2004

In oil-filled enuipment such as transformers, partial discharge or local overheating will precede a final shutdown. Accompanied with such problems is a decomposition of insulating material into gases, which are dissolved into the transformer oil. The gases dissolved in oil can be separated with some membranes based on the differences in permeability of membranes to different gases. This paper discuss the permeability characteristics of several membranes for separation hydrogen gas in oil. With result of this paper, it may become possible to detect fault-related gases from transformer oil and predict incipient failures in the future.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.546-552
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• 2010

The achievement of high gas permeability is a key factor in the development of porous SiC ceramics for applications of hot gas filter, vacuum chuck, and air spindle. However, few reports on the gas permeability of porous SiC ceramics can be found in the literature. In this paper, porous SiC ceramics were fabricated at temperatures ranging from $1600^{\circ}C$ to $1800^{\circ}C$ using the mixing powders of SiC, silicon, carbon and boron as starting materials. In some samples, expanded hollow microspheres as a pore former were used to make a cellular pore structure. It was possible to produce Si bonded SiC ceramics with porosities ranging from 42% to 55%. The maximum bending strength was 58MPa for the carbon content of 0.2 wt% and sintering temperature of $1700^{\circ}C$. The increase of air permeability was accelerated by addition of hollow microsphere as a pore former.

• Polymer(Korea)
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• v.26 no.3
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• pp.381-388
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• 2002

The properties of polyurethane (PU) nanocomposites with organoclay have been compared in terms of their thermo-mechanical properties, morphology, and gas permeability. Hexadecylamine-montmorillonite ($C_{16}$-MMT) was used as an organoclay to make PU hybrid films. The properties were investigated as a function of organoclay content (1-4 wt%) in the PU matrix. Transmission electron microscopy (TEM) photographs showed that most clay layers were dispersed homogeneously into the matrix polymer in nano-scale, although some particles of clay were agglomerated. We also found that the addition of only a small amount of organoclay was enough to improve the thermal stabilities and mechanical properties of PU hybrid films while gas permeability was reduced. Even at low organoclay content (<5 wt%), the PU nanocomposite showed much better thermo-mechanical properties, and lower gas permeability than pure PU.

• Geomechanics and Engineering
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• v.24 no.6
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• pp.519-529
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• 2021

In coal mining activities, the abutment stress of the coal has to undergo cyclic loading and unloading, affecting the strength and seepage characteristics of coal; additionally, it can cause dynamic disasters, posing a major challenge for the safety of coal mine production. To improve the understanding of the dynamic disaster mechanism of gas outburst and rock burst coupling, triaxial devices are applied to axial pressure cyclic loading-unloading tests under different axial stress peaks and different pore pressures. The existing empirical formula is use to perform a non-linear regression fitting on the relationship between stress and permeability, and the damage rate of permeability is introduced to analyze the change in permeability. The results show that the permeability curve obtained had "memory", and the peak stress was lower than the conventional loading path. The permeability curve and the volume strain curve show a clear symmetrical relationship, being the former in the form of a negative power function. Owing to the influence of irreversible deformation, the permeability difference and the damage of permeability mainly occur in the initial stage of loading-unloading, and both decrease as the number of cycles of loading-unloading increase. At the end of the first cycle and the second cycle, the permeability decreased in the range of 5.777 - 8.421 % and 4.311-8.713 %, respectively. The permeability decreases with an increase in the axial stress peak, and the damage rate shows the opposite trend. Under the same conditions, the permeability of methane is always lower than that of helium, and it shows a V-shape change trend with increasing methane pressures, and the permeability of the specimen was 3 MPa > 1 MPa > 2 MPa.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.192-195
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• 2008

Conventional gas deposits consist of pressurized gas held in porous and permeable reservoir rocks and its recovery takes place where the natural pressure of the gas reservoir forces gas to the surface. But gas hydrate is a crystalline solid, its prospects require reservoir rock properties approprate porosity, permeability with mapping of temperature and pressure conditions to define the hydrate stability zone. In this study, we have carried out to investigate the dissociation characteristics of methane hydrates and the productivities of dissociated gas and water with depressurization scheme. Also, it has been conducted the flowing behavior of the dissociated gas and water in porous rock and the efficiency of the production.

• Polymer(Korea)
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• v.28 no.5
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• pp.374-381
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• 2004

Gas permeability of low density polyethylene (LDPE) film containing zeolite powder for $CO_2,\;O_2$ and $N_2$ were investigated. Zeolite powders modified by cations or surfactant were compounded with LDPE to produce $20 wt\%$ masterbatch. After blending the masterbatch with LDPE, zeolite filled films were prepared by the blown film process. Finally, the composite films containing zeolite loadings of 0, 3,5, and $10 wt\%$ were produced. A gas permeability apparatus based on the variable volume principle was designed to analyze the characteristics of films. Experiments showed a general trend that gas permeabilities first decreased and then increased as the zeolite content was increased. Surfactant modified zeolite showed a better interfacial adhesion with the matrix, but the film did not show a discernible difference in gas permeability compared with the other modified films. The difference of temperature dependences in the gas permeabilities of composite films was slightly smaller than that of LDPE film.

• Membrane Journal
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• v.24 no.4
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• pp.325-331
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• 2014

We synthesized novel polyimides with high gas permeability and selectivity for application of on board inert gas generation system (OBIGGS). 2,2-bis(3,4-carboxylphenyl) hexafluoropropane dianhydride (6FDA) and two kinds of amines with high permeability and solubility were used to prepare the novel polymide. 2,3,5,6-Tetramethyl-1,4-phenylenediamine (TMPD) was used to improve gas permeability and various kinds of diamines were used to improve the gas selectivity respectively. The polyimide copolymers were synthesized by commercial chemical imidization method and their average molecular weights were over 100,000g/mol. The glass temperature ($T_g$) and the thermal degradation temperature were characterized using differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The synthesized copolymers showed high $T_g$ over $300^{\circ}C$ and high thermal degradation temperature over $500^{\circ}C$. The gas permeation properties were measured by time-lag equipment. Although general polyimides showed very low gas permeability, synthesized polyimide copolymer showed high $O_2$ permeability of 36.21 barrer with high $O_2/N_2$ selectivity around 4.1. From this result, we confirm that these membranes have possibility to apply to OBIGGS.