The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Jun Yao - One of the best experts on this subject based on the ideXlab platform.
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Characterization of gas transport behaviors in shale gas and tight gas reservoirs by digital rock analysis
International Journal of Heat and Mass Transfer, 2016Co-Authors: Hai Sun, Jun Yao, Ying-chang Cao, Dongyan Fan, Lei ZhangAbstract:Abstract Due to the extremely tiny pore size of tight gas and shale gas reservoir, the modified Darcy’s law in which the intrinsic permeability is replaced by the apparent permeability that can be obtained by a function of three transport parameters (intrinsic permeability, porosity and tortuosity), is used to describe the combined mechanisms of viscous flow, Knudsen Diffusion, the effect of the adsorbed layer thickness and surface Diffusion through the adsorbed layer. A new apparent permeability estimation method based on digital rock was proposed in this paper. The digital rock with nanopores could be constructed by 3D pore structure images obtained from micro/nano CT and FIB-SEM images directly or reconstructed with Markov Chain Monte Carlo (MCMC) method from the 2D SEM images of pore structure; then Lattice Boltzmann method can be applied to calculate the intrinsic permeability, porosity and tortuosity of 3D digital rock. These parameters are used to calculate the apparent permeability under consideration of different combined gas transport mechanisms. This method is applied to samples from the shale gas reservoir in Silurian Longmaxi Formation of Sichuan Basin and from the tight gas reservoir in the Wenchang Formation of Huizhou Sag. The results show that all considered transport mechanisms greatly impact the shale apparent permeability and cannot be ignored in shale samples. In tight gas reservoirs, Knudsen Diffusion is an important mechanism at low pressures of less than 1 MPa. However, Knudsen Diffusion could be ignored when pressure is greater than 1 MPa due to its smaller impact.
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Apparent gas permeability in an organic-rich shale reservoir
Fuel, 2016Co-Authors: Wenhui Song, Jianlin Zhao, Hai Sun, Yang Li, Jun Yao, Yongfei Yang, Lei Zhang, Hongguang SuiAbstract:Accurate models of gas transport in shale gas reservoirs must consider complex gas transport mechanisms and phase behavior in nanopores, as well as different pore types. The gas transport mechanisms in shale gas reservoirs include viscous flow, Knudsen Diffusion, surface Diffusion, adsorption and desorption. In this study, a unified model of nanopore gas transport in shale gas reservoirs is presented. Gas storage patterns are different in organic pores and inorganic pores. Therefore, we develop two fully coupled apparent permeability models to describe gas transport in organic pores and inorganic pores separately. The apparent permeability model of organic pores considers the gas transport mechanisms of viscous flow, Knudsen Diffusion, surface Diffusion, adsorption and desorption. The apparent permeability model of inorganic pores considers the gas transport mechanisms of viscous flow and Knudsen Diffusion. In both models, stress dependence, real gas effects and phase behavior are taken into account. Then, the influences of pore pressure, effective stress, real gas effects, pore radius, phase behaviors and transport properties on apparent gas permeabilities in organic pores and inorganic pores are analyzed based on the proposed models.
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Influence of gas transport mechanisms on the productivity of multi-stage fractured horizontal wells in shale gas reservoirs
Petroleum Science, 2015Co-Authors: Wei Wang, Hai Sun, Jun Yao, Wenhui SongAbstract:In order to investigate the influence on shale gas well productivity caused by gas transport in nanometer-size pores, a mathematical model of multi-stage fractured horizontal wells in shale gas reservoirs is built, which considers the influence of viscous flow, Knudsen Diffusion, surface Diffusion, and adsorption layer thickness. A discrete-fracture model is used to simplify the fracture modeling, and a finite element method is applied to solve the model. The numerical simulation results indicate that with a decrease in the intrinsic matrix permeability, Knudsen Diffusion and surface Diffusion contributions to production become large and cannot be ignored. The existence of an adsorption layer on the nanopore surfaces reduces the effective pore radius and the effective porosity, resulting in low production from fractured horizontal wells. With a decrease in the pore radius, considering the adsorption layer, the production reduction rate increases. When the pore radius is less than 10 nm, because of the combined impacts of Knudsen Diffusion, surface Diffusion, and adsorption layers, the production of multi-stage fractured horizontal wells increases with a decrease in the pore pressure. When the pore pressure is lower than 30 MPa, the rate of production increase becomes larger with a decrease in pore pressure.
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Nanoscale simulation of shale transport properties using the lattice Boltzmann method: permeability and diffusivity
Scientific reports, 2015Co-Authors: Li Chen, Jun Yao, Lei Zhang, Qinjun Kang, Wen-quan TaoAbstract:Porous structures of shales are reconstructed based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analyzes of the nanoscale reconstructed shales are performed, including porosity, pore size distribution, specific surface area and pore connectivity. The multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) fluid flow model and single-relaxation-time (SRT) LBM Diffusion model are adopted to simulate the fluid flow and Knudsen Diffusion process within the reconstructed shales, respectively. Tortuosity, intrinsic permeability and effective Knudsen diffusivity are numerically predicted. The tortuosity is much higher than that commonly employed in Bruggeman equation. Correction of the intrinsic permeability by taking into consideration the contribution of Knudsen Diffusion, which leads to the apparent permeability, is performed. The correction factor under different Knudsen number and pressure are estimated and compared with existing corrections reported in the literature. For the wide pressure range under investigation, the correction factor is always greater than 1, indicating the Knudsen Diffusion always plays a role on the transport mechanisms of shale gas in shales studied in the present study. Most of the values of correction factor are located in the transition regime, with no Darcy flow regime observed.
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Numerical simulation of gas transport mechanisms in tight shale gas reservoirs
Petroleum Science, 2013Co-Authors: Jun Yao, Hai Sun, Dongyan Fan, Chenchen Wang, Zhixue SunAbstract:Due to the nanometer scale pore size and extremely low permeability of a shale matrix, traditional Darcy’s law can not exactly describe the combined gas transport mechanisms of viscous flow and Knudsen Diffusion. Three transport models modified by the Darcy equation with apparent permeability are used to describe the combined gas transport mechanisms in ultra-tight porous media, the result shows that Knudsen Diffusion has a great impact on the gas transport and Darcy’s law cannot be used in a shale matrix with a pore diameter less than 1 μm. A single porosity model and a double porosity model with consideration of the combined gas transport mechanisms are developed to evaluate the influence of gas transport mechanisms and fracture parameters respectively on shale gas production. The numerical results show that the gas production predicted by Darcy’s law is lower than that predicted with consideration of Knudsen Diffusion and the tighter the shale matrix, the greater difference of the gas production estimates. In addition, the numerical simulation results indicate that shale fractures have a great impact on shale gas production. Shale gas cannot be produced economically without fractures.
Youichi Negishi - One of the best experts on this subject based on the ideXlab platform.
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Analysis of a two-stage membrane reactor integrated with porous membrane having Knudsen Diffusion characteristics for the thermal decomposition of hydrogen sulfide
Journal of Membrane Science, 2000Co-Authors: Hirofumi Ohashi, Youichi Negishi, Haruhiko Ohya, Masahiko Aihara, Takashi Takeuchi, Jun Fan, Svetlana I. SemenovaAbstract:Abstract Using basic equation for material balance, the thermal decomposition of hydrogen sulfide to produce hydrogen was investigated in a two-stage membrane reactor integrated with porous membrane having Knudsen Diffusion characteristics. It was evaluated the effect of membrane area ratio S m,P / S m,R and the pressure in the 1st permeate chamber p P 1 on H 2 concentration in the 2nd permeate chamber y H 2 ,P 2 and the flow rate of H 2 in the 2nd U H 2 . With the decrease of S m,P / S m,R , y H 2 ,P 2 increases and takes constant value which is larger than the H 2 concentration in the permeate chamber for the single-stage membrane reactor by about 1.7 times. There is ( S m,P / S m,R ) limit corresponding to the condition that no flow in the 1st permeate chamber. With the increase of S m,P / S m,R , U H 2 increases and takes maximum value U H 2 ,max at ( S m,P / S m,R ) limit . There is an optimum p P 1 for higher U H 2 ,max , but the difference between the highest value of U H 2 ,max and the lowest one is small. The maximum value of U H 2 ,max is larger than the amount of H 2 obtained in the single-stage by about 1.1 times.
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effect of membrane on yield of equilibrium reaction â case i h2sâh2 1 xsx with membrane of Knudsen Diffusion characteristics
Journal of Membrane Science, 1999Co-Authors: Jun Fan, Youichi Negishi, Haruhiko Ohya, Masahiko Aihara, Hirofumi Ohashi, Takashi Takeuchi, Svetlana I. SemenovaAbstract:Abstract Using mathematical model and experimental method, the thermal and non-catalytic decomposition of hydrogen sulfide in membrane reactor with porous membrane of Knudsen Diffusion characteristics was investigated. It was found that in terms of the yield, the membrane reactor can have its merit over the reactor without membrane in the case where inverse of space velocity 1/ S v is larger than some critical value, and there is a maximum value of specific yield SY defined as the ratio of yield for the membrane reactor to that for the reactor without membrane, SY max when almost all the reactant permeates through the membrane. Lower a product of permeance P H 2 and the ratio of membrane area to reactor volume 1/ h , P H 2 / h and higher pressure in the main chamber p R is favorable to obtain higher SY max and the average concentration of H 2 in the permeate. But the reactor length needed to permeate almost all the reactant increases. There might exist optimum P H 2 / h from the viewpoint of cost. Using membrane reactor integrated with ZrO 2 –SiO 2 composite membrane, the reaction was carried out under the following conditions: T =973 and 1023 K, p R =0.11 and 0.20 MPa, pressure in the permeate chamber of 5 kPa and 1/ S v =21–77 s. With the experimental condition, T =1023 K, p R =0.11 MPa and 1/ S v =77 s, SY was 0.35 in maximum. The experimental results were compared with the results of the mathematical analysis. The agreement between both the results is found rather good at a lower reacting temperature, but not so good at a higher reacting temperature.
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Effect of membrane on yield of equilibrium reaction â case I: H2SâH2+1/xSx with membrane of Knudsen Diffusion characteristics
Journal of Membrane Science, 1999Co-Authors: Jun Fan, Youichi Negishi, Haruhiko Ohya, Masahiko Aihara, Hirofumi Ohashi, Takashi Takeuchi, Svetlana I. SemenovaAbstract:Abstract Using mathematical model and experimental method, the thermal and non-catalytic decomposition of hydrogen sulfide in membrane reactor with porous membrane of Knudsen Diffusion characteristics was investigated. It was found that in terms of the yield, the membrane reactor can have its merit over the reactor without membrane in the case where inverse of space velocity 1/ S v is larger than some critical value, and there is a maximum value of specific yield SY defined as the ratio of yield for the membrane reactor to that for the reactor without membrane, SY max when almost all the reactant permeates through the membrane. Lower a product of permeance P H 2 and the ratio of membrane area to reactor volume 1/ h , P H 2 / h and higher pressure in the main chamber p R is favorable to obtain higher SY max and the average concentration of H 2 in the permeate. But the reactor length needed to permeate almost all the reactant increases. There might exist optimum P H 2 / h from the viewpoint of cost. Using membrane reactor integrated with ZrO 2 –SiO 2 composite membrane, the reaction was carried out under the following conditions: T =973 and 1023 K, p R =0.11 and 0.20 MPa, pressure in the permeate chamber of 5 kPa and 1/ S v =21–77 s. With the experimental condition, T =1023 K, p R =0.11 MPa and 1/ S v =77 s, SY was 0.35 in maximum. The experimental results were compared with the results of the mathematical analysis. The agreement between both the results is found rather good at a lower reacting temperature, but not so good at a higher reacting temperature.
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Characteristics of a zirconia composite membrane fabricated by a laser firing method
Journal of Membrane Science, 1996Co-Authors: Haruhiko Ohya, Masahiko Aihara, Takeshi Onodera, Youichi NegishiAbstract:Abstract By a method of laser firing, a high zirconia containing (70%) composite membrane on porous ceramic tubing was successfully fabricated. The laser sintered composite membrane was characterized by gas separation/permeation experiments. In the separation experiment of a CO 2 CH 4 gaseous mixture, it was found that the separation factor of CH 4 over CO 2 was 1.15. In the pure gases permeation experiment, it was found that Knudsen Diffusion is considered to be predominant in the permeation mechanism for pure gases H 2 , He, CH 4 , N 2 , O 2 , and CO 2 , and the permeation mechanism of H 2 O at lower temperature depends mainly on surface Diffusion and on Knudsen Diffusion at higher temperature.
Lei Zhang - One of the best experts on this subject based on the ideXlab platform.
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Characterization of gas transport behaviors in shale gas and tight gas reservoirs by digital rock analysis
International Journal of Heat and Mass Transfer, 2016Co-Authors: Hai Sun, Jun Yao, Ying-chang Cao, Dongyan Fan, Lei ZhangAbstract:Abstract Due to the extremely tiny pore size of tight gas and shale gas reservoir, the modified Darcy’s law in which the intrinsic permeability is replaced by the apparent permeability that can be obtained by a function of three transport parameters (intrinsic permeability, porosity and tortuosity), is used to describe the combined mechanisms of viscous flow, Knudsen Diffusion, the effect of the adsorbed layer thickness and surface Diffusion through the adsorbed layer. A new apparent permeability estimation method based on digital rock was proposed in this paper. The digital rock with nanopores could be constructed by 3D pore structure images obtained from micro/nano CT and FIB-SEM images directly or reconstructed with Markov Chain Monte Carlo (MCMC) method from the 2D SEM images of pore structure; then Lattice Boltzmann method can be applied to calculate the intrinsic permeability, porosity and tortuosity of 3D digital rock. These parameters are used to calculate the apparent permeability under consideration of different combined gas transport mechanisms. This method is applied to samples from the shale gas reservoir in Silurian Longmaxi Formation of Sichuan Basin and from the tight gas reservoir in the Wenchang Formation of Huizhou Sag. The results show that all considered transport mechanisms greatly impact the shale apparent permeability and cannot be ignored in shale samples. In tight gas reservoirs, Knudsen Diffusion is an important mechanism at low pressures of less than 1 MPa. However, Knudsen Diffusion could be ignored when pressure is greater than 1 MPa due to its smaller impact.
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Apparent gas permeability in an organic-rich shale reservoir
Fuel, 2016Co-Authors: Wenhui Song, Jianlin Zhao, Hai Sun, Yang Li, Jun Yao, Yongfei Yang, Lei Zhang, Hongguang SuiAbstract:Accurate models of gas transport in shale gas reservoirs must consider complex gas transport mechanisms and phase behavior in nanopores, as well as different pore types. The gas transport mechanisms in shale gas reservoirs include viscous flow, Knudsen Diffusion, surface Diffusion, adsorption and desorption. In this study, a unified model of nanopore gas transport in shale gas reservoirs is presented. Gas storage patterns are different in organic pores and inorganic pores. Therefore, we develop two fully coupled apparent permeability models to describe gas transport in organic pores and inorganic pores separately. The apparent permeability model of organic pores considers the gas transport mechanisms of viscous flow, Knudsen Diffusion, surface Diffusion, adsorption and desorption. The apparent permeability model of inorganic pores considers the gas transport mechanisms of viscous flow and Knudsen Diffusion. In both models, stress dependence, real gas effects and phase behavior are taken into account. Then, the influences of pore pressure, effective stress, real gas effects, pore radius, phase behaviors and transport properties on apparent gas permeabilities in organic pores and inorganic pores are analyzed based on the proposed models.
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Nanoscale simulation of shale transport properties using the lattice Boltzmann method: permeability and diffusivity
Scientific reports, 2015Co-Authors: Li Chen, Jun Yao, Lei Zhang, Qinjun Kang, Wen-quan TaoAbstract:Porous structures of shales are reconstructed based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analyzes of the nanoscale reconstructed shales are performed, including porosity, pore size distribution, specific surface area and pore connectivity. The multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) fluid flow model and single-relaxation-time (SRT) LBM Diffusion model are adopted to simulate the fluid flow and Knudsen Diffusion process within the reconstructed shales, respectively. Tortuosity, intrinsic permeability and effective Knudsen diffusivity are numerically predicted. The tortuosity is much higher than that commonly employed in Bruggeman equation. Correction of the intrinsic permeability by taking into consideration the contribution of Knudsen Diffusion, which leads to the apparent permeability, is performed. The correction factor under different Knudsen number and pressure are estimated and compared with existing corrections reported in the literature. For the wide pressure range under investigation, the correction factor is always greater than 1, indicating the Knudsen Diffusion always plays a role on the transport mechanisms of shale gas in shales studied in the present study. Most of the values of correction factor are located in the transition regime, with no Darcy flow regime observed.
Svetlana I. Semenova - One of the best experts on this subject based on the ideXlab platform.
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Analysis of a two-stage membrane reactor integrated with porous membrane having Knudsen Diffusion characteristics for the thermal decomposition of hydrogen sulfide
Journal of Membrane Science, 2000Co-Authors: Hirofumi Ohashi, Youichi Negishi, Haruhiko Ohya, Masahiko Aihara, Takashi Takeuchi, Jun Fan, Svetlana I. SemenovaAbstract:Abstract Using basic equation for material balance, the thermal decomposition of hydrogen sulfide to produce hydrogen was investigated in a two-stage membrane reactor integrated with porous membrane having Knudsen Diffusion characteristics. It was evaluated the effect of membrane area ratio S m,P / S m,R and the pressure in the 1st permeate chamber p P 1 on H 2 concentration in the 2nd permeate chamber y H 2 ,P 2 and the flow rate of H 2 in the 2nd U H 2 . With the decrease of S m,P / S m,R , y H 2 ,P 2 increases and takes constant value which is larger than the H 2 concentration in the permeate chamber for the single-stage membrane reactor by about 1.7 times. There is ( S m,P / S m,R ) limit corresponding to the condition that no flow in the 1st permeate chamber. With the increase of S m,P / S m,R , U H 2 increases and takes maximum value U H 2 ,max at ( S m,P / S m,R ) limit . There is an optimum p P 1 for higher U H 2 ,max , but the difference between the highest value of U H 2 ,max and the lowest one is small. The maximum value of U H 2 ,max is larger than the amount of H 2 obtained in the single-stage by about 1.1 times.
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effect of membrane on yield of equilibrium reaction â case i h2sâh2 1 xsx with membrane of Knudsen Diffusion characteristics
Journal of Membrane Science, 1999Co-Authors: Jun Fan, Youichi Negishi, Haruhiko Ohya, Masahiko Aihara, Hirofumi Ohashi, Takashi Takeuchi, Svetlana I. SemenovaAbstract:Abstract Using mathematical model and experimental method, the thermal and non-catalytic decomposition of hydrogen sulfide in membrane reactor with porous membrane of Knudsen Diffusion characteristics was investigated. It was found that in terms of the yield, the membrane reactor can have its merit over the reactor without membrane in the case where inverse of space velocity 1/ S v is larger than some critical value, and there is a maximum value of specific yield SY defined as the ratio of yield for the membrane reactor to that for the reactor without membrane, SY max when almost all the reactant permeates through the membrane. Lower a product of permeance P H 2 and the ratio of membrane area to reactor volume 1/ h , P H 2 / h and higher pressure in the main chamber p R is favorable to obtain higher SY max and the average concentration of H 2 in the permeate. But the reactor length needed to permeate almost all the reactant increases. There might exist optimum P H 2 / h from the viewpoint of cost. Using membrane reactor integrated with ZrO 2 –SiO 2 composite membrane, the reaction was carried out under the following conditions: T =973 and 1023 K, p R =0.11 and 0.20 MPa, pressure in the permeate chamber of 5 kPa and 1/ S v =21–77 s. With the experimental condition, T =1023 K, p R =0.11 MPa and 1/ S v =77 s, SY was 0.35 in maximum. The experimental results were compared with the results of the mathematical analysis. The agreement between both the results is found rather good at a lower reacting temperature, but not so good at a higher reacting temperature.
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Effect of membrane on yield of equilibrium reaction â case I: H2SâH2+1/xSx with membrane of Knudsen Diffusion characteristics
Journal of Membrane Science, 1999Co-Authors: Jun Fan, Youichi Negishi, Haruhiko Ohya, Masahiko Aihara, Hirofumi Ohashi, Takashi Takeuchi, Svetlana I. SemenovaAbstract:Abstract Using mathematical model and experimental method, the thermal and non-catalytic decomposition of hydrogen sulfide in membrane reactor with porous membrane of Knudsen Diffusion characteristics was investigated. It was found that in terms of the yield, the membrane reactor can have its merit over the reactor without membrane in the case where inverse of space velocity 1/ S v is larger than some critical value, and there is a maximum value of specific yield SY defined as the ratio of yield for the membrane reactor to that for the reactor without membrane, SY max when almost all the reactant permeates through the membrane. Lower a product of permeance P H 2 and the ratio of membrane area to reactor volume 1/ h , P H 2 / h and higher pressure in the main chamber p R is favorable to obtain higher SY max and the average concentration of H 2 in the permeate. But the reactor length needed to permeate almost all the reactant increases. There might exist optimum P H 2 / h from the viewpoint of cost. Using membrane reactor integrated with ZrO 2 –SiO 2 composite membrane, the reaction was carried out under the following conditions: T =973 and 1023 K, p R =0.11 and 0.20 MPa, pressure in the permeate chamber of 5 kPa and 1/ S v =21–77 s. With the experimental condition, T =1023 K, p R =0.11 MPa and 1/ S v =77 s, SY was 0.35 in maximum. The experimental results were compared with the results of the mathematical analysis. The agreement between both the results is found rather good at a lower reacting temperature, but not so good at a higher reacting temperature.
Chenchen Wang - One of the best experts on this subject based on the ideXlab platform.
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A Unified Model for Gas Transfer in Nanopores of Shale-Gas Reservoirs: Coupling Pore Diffusion and Surface Diffusion
SPE Journal, 2016Co-Authors: Chaohua Guo, Chenchen Wang, Zhangxin ChenAbstract:Summary A model for gas transfer in nanopores is the basis for accurate numerical simulation, which has important implications for economic development of shale-gas reservoirs (SGRs). The gas-transfer mechanism in SGRs is significantly different from that of conventional gas reservoirs, which is mainly caused by the nanoscale phenomena and organic matter as a medium of gas sourcing and storage. The gas-transfer mechanism includes bulk-gas transfer and adsorption-gas surface Diffusion in nanopores of SGRs, where the bulk-gas-transfer mechanism includes continuous flow, slip flow, and Knudsen Diffusion. First, a model for bulk-gas transfer in nanopores was established, which was dependent on slip flow and Knudsen Diffusion. The total gas flux in the bulk phase is not a simple sum of slip-flow flux and Knudsen-Diffusion flux but a weighted sum on the basis of corresponding contributions. The weighted factors are primarily controlled by the mutual interaction between slip flow and Knudsen Diffusion, which is determined by probabilities between gas molecules colliding with each other and colliding with nanopore surface in this newly proposed model. Second, a model for adsorbed-gas surface Diffusion in nanopores was established, which was modeled after the Hwang and Kammermeyer (1966) model and considered the effect of gas coverage under a high-pressure condition. Finally, with the combination of these two models, a unified model for gas transport in nanopores of SGRs was established, and this model was validated through molecular simulation and experimental data. Results show that: Slip flow makes a great contribution to gas transfer under the condition of meso/macropores (pore radius greater than 2 nm) and high pressure. Knudsen Diffusion makes an important contribution to gas transfer under the condition of macropores (pore radius greater than 50 nm) and less than 1 MPa in pressure, whereas it can be ignored in other cases. A surface-Diffusion coefficient is comparable with a pore-Diffusion coefficient, and gas transfer is always dominated by surface Diffusion over all the ranges of pressure in micropores (pore radius ≤ 2 nm). Surface-Diffusion contribution decreases with an increase in pore size, isosteric sorption heat, pressure, and temperature in SGRs.
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A Model for Gas Transport in Micro Fractures of Shale and Tight Gas Reservoirs
Day 1 Tue October 20 2015, 2015Co-Authors: Chenchen Wang, Zhangxin ChenAbstract:Abstract A model for gas transport in micro fractures of shale and tight gas reservoirs is established. Slip flow and Knudsen Diffusion are coupled together to describe general gas transport mechanisms, which include continuous flow, slip flow, transitional flow and Knudsen Diffusion. The ratios of the intermolecular collision frequency and the molecule-wall collision frequency to the total collision frequency are defined as the weight coefficients of slip flow and Knudsen Diffusion, respectively. The model is validated by molecular simulation results. The results show that: (1) the model can reasonably describe the process of the mass transform of different gas transport mechanisms; (2) fracture geometry significantly impacts gas transport. Under the same fracture aperture, the higher the aspect ratio is, the stronger the gas transport capacity, and this phenomenon is more pronounced in the cases with higher gas pressure and larger fracture aperture.
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a model for gas transport in microfractures of shale and tight gas reservoirs
Aiche Journal, 2015Co-Authors: Keliu Wu, Xiangfang Li, Chenchen Wang, Zhangxin Chen, Wei YuAbstract:A model for gas transport in microfractures of shale and tight gas reservoirs is established. Slip flow and Knudsen Diffusion are coupled together to describe general gas transport mechanisms, which include continuous flow, slip flow, transitional flow, and Knudsen Diffusion. The ratios of the intermolecular collision frequency and the molecule-wall collision frequency to the total collision frequency are defined as the weight coefficients of slip flow and Knudsen Diffusion, respectively. The model is validated by molecular simulation results. The results show that: (1) the model can reasonably describe the process of the mass transform of different gas transport mechanisms; (2) fracture geometry significantly impacts gas transport. Under the same fracture aperture, the higher the aspect ratio is, the stronger the gas transport capacity, and this phenomenon is more pronounced in the cases with higher gas pressure and larger fracture aperture. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2079–2088, 2015
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Apparent Permeability for Gas Flow in Shale Reservoirs Coupling Effects of Gas Diffusion and Desorption
Proceedings of the 2nd Unconventional Resources Technology Conference, 2014Co-Authors: Chenchen Wang, Zhangxing ChenAbstract:Gas transport mechanism and apparent permeability in shale reservoirs are significantly different from those in conventional gas reservoirs, which are mainly caused by the nanoscale phenomena and organic matter as being the media of gas storing and sourcing. However, gas flow behavior plays a significant role in well performance in shale reservoirs. Hence, development of a new apparent permeability model considering gas transport mechanism is critically desirable. In this work, we propose a new apparent permeability model describing gas flow in nanopores of shale gas reservoirs by integrating bulk gas flow in nanopores and gas desorption from nanopores wall. Although the mean free path of gas molecule is similar to the order of nanopore diameter, gas flow in nanopores should combine viscous flow and Knudsen Diffusion together. The total gas flux should not be a simple summation of viscous flow flux and Knudsen Diffusion flux, but a weighted summation based on their different contributions. The weighted factor is primarily controlled by the interaction between viscous flow and Knudsen Diffusion, which can be quantified by probabilities between gas molecules colliding with each other and colliding with nanopores wall in the new model. The apparent permeability considering gas desorption is established based on Langmuir isotherm equation and mass balance equation. The new model can accurately calculate the apparent permeability from viscous flow, Knudsen Diffusion, and desorption, respectively. Furthermore, it can provide critical insights into understanding the mechanisms of bulk gas flow and gas desorption from nanopores wall. Also, it can be used to develop the new generation reservoir simulator in shale reservoirs.
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Numerical simulation of gas transport mechanisms in tight shale gas reservoirs
Petroleum Science, 2013Co-Authors: Jun Yao, Hai Sun, Dongyan Fan, Chenchen Wang, Zhixue SunAbstract:Due to the nanometer scale pore size and extremely low permeability of a shale matrix, traditional Darcy’s law can not exactly describe the combined gas transport mechanisms of viscous flow and Knudsen Diffusion. Three transport models modified by the Darcy equation with apparent permeability are used to describe the combined gas transport mechanisms in ultra-tight porous media, the result shows that Knudsen Diffusion has a great impact on the gas transport and Darcy’s law cannot be used in a shale matrix with a pore diameter less than 1 μm. A single porosity model and a double porosity model with consideration of the combined gas transport mechanisms are developed to evaluate the influence of gas transport mechanisms and fracture parameters respectively on shale gas production. The numerical results show that the gas production predicted by Darcy’s law is lower than that predicted with consideration of Knudsen Diffusion and the tighter the shale matrix, the greater difference of the gas production estimates. In addition, the numerical simulation results indicate that shale fractures have a great impact on shale gas production. Shale gas cannot be produced economically without fractures.
