Fractal-based real gas flow model in shales: An interplay of nano-pore and nano-fracture networks

Li, Yudan; Kalantari-Dahaghi, Amirmasoud; Zolfaghari, Arsalan; Dong, Pingchuan; Negahban, Shahin; Zhou, Dawei

doi:10.1016/j.ijheatmasstransfer.2018.08.077

Cited by 36 publications

(19 citation statements)

References 61 publications

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“…Note that, in addition to the LBM and PNM, there are also other approaches to realize the pore-scale predictions, such as fractal theory − and the finite element method (FEM). − Generally, the fractal model describes the flow in porous media by taking account the key parameters of the porous structure into the analytical model (for instance, porosity, tortuosity, and connectivity). In this case, the fractal model is more similar to the theoretical method, rather than to conduct the pore-scale simulations in the porous media.…”

Section: Pore-scale Simulationsmentioning

confidence: 99%

Transport of Shale Gas in Microporous/Nanoporous Media: Molecular to Pore-Scale Simulations

Fan

et al. 2020

Energy Fuels

136

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As the typical unconventional reservoir, shale gas is believed to be the most promising alternative for the conventional resources in future energy patterns, attracting more and more attention throughout the world. Generally, the majority of shale gas is trapped within the tight shale rock with ultralow porosity (<10%) and ultrasmall pore size (as less as several nanometers). Thus, the accurate understanding of gas transport characteristic and its underlying mechanism through these microporous/nanoporous media is critical for the effective exploitation of shale reservoir. In this context, we present a comprehensive review on the current advances of multiscale transport simulations of shale gas in microporous/nanoporous media from molecular to pore-scale. For the gas transport in shale nanopores using molecular dynamics (MD) simulations, the structure and force parameters of various nanopore models, including organic models (graphene, carbon nanotubes, and kerogen) and inorganic models (clays, carbonate, and quartz), and flow simulation strategies (such as nonequilibrium molecular dynamics (NEMD) and Grand Canonical Monte Carlo simulations) are systematically introduced and clarified. The significant MD simulation results about gas transport characteristic in shale nanopores then are elaborated respectively for different factors, including pore size, ambient pressure, nanopore type, atomistic roughness, and pore structure, as well as multicomponent. Besides, the two-phase transport characteristic of gas and water is also discussed, considering the ubiquity of water in shale formation. For the lattice Boltzmann method (LBM) and pore network model (PNM) approaches to conduct pore-scale simulations, we briefly review its origins, modifications, and applications for gas transport simulations in a microporous/nanoporous shale matrix. Particularly, the upscaling methods to incorporate MD simulation into LBM and PNM frameworks are emphatically expounded in the light of recent attempts of MD-based pore-scale simulations. It is hoped that this Review would be helpful for the readers to build a systematical overview on the transport characteristic of shale gas in microporous/nanoporous media and subsequently accelerate the development of the shale industry.

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Section: Pore-scale Simulationsmentioning

confidence: 99%

Transport of Shale Gas in Microporous/Nanoporous Media: Molecular to Pore-Scale Simulations

Fan

et al. 2020

Energy Fuels

136

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“…Actually, despite a lot of influence factors or mechanisms (e.g., water film and surface diffusion) being considered and accumulated by these analytical models, − the core of these frameworks is still the slip model, which is the most essential feature of gas flow on the nanoscale. Table lists the basic slip models ,− employed in the recent theoretical studies − ,− of shale gas transport through nanopores. It can be found that these slip models are generally established in the fields of microelectro-mechanical system (MEMS) and rarefied gas flow, which are significantly different from the nanoscale gas flow of shale reservoirs.…”

Section: Introductionmentioning

confidence: 99%

“…On the basis of advanced experimental methods, 19,20 such as scanning transmission X-ray microscopy, transmission electron microcopy, and 13 C nuclear magnetic resonance (NMR), the physical and chemical structures of kerogen have been revealed, indicating that kerogen is constructed of numerous organic macromolecular skeletons containing various chemical elements: C (carbon), O (oxygen), N (nitrogen), S (sulfur), and H (hydrogen). Although the molecular formula of kerogen (C x H y O z N m S n ) varies for different types and maturities, carbon occupies an absolute majority (as much as 90%) of all elements.…”

Section: Introductionmentioning

confidence: 99%

“…The other strategy is presenting gas transport in the kerogen matrix constructed of abundant kerogen molecules (fragments). In this aspect, Obliger et al 37,38 simulated hydrocarbon permeation in the kerogen microstructure with a disordered pore network, considering the impact of nanoporosity and multiple component mixtures, and found that the permeation scales with the reciprocal of alkane length and decreases with the number of disordered particles; Wu and Firoozabadi 39 studied the effect of microstructural flexibility on methane flow in the kerogen matrix at different pressures via compressing a collection of 60 kerogen macromolecules, demonstrating the significant influence of flexibility of the kerogen structure on gas diffusion; Vasileiadis et al 40 investigated the role of porosity on the adsorption and transport behavior of CH 4 , N 2 , C 2 H 6 , and CO 2 in type II "smooth surface," "MEMS," "rarefied gas" Chai et al 10 B−K model 9 Sun et al 8 B−K model 9 Javadpour 5 Brown model 15 "copper pipes," "channel size of 10.1 cm," "ultralow pressure (0.001 bar)" Guo et al 11 Brown model 15 Su et al 12 Brown model 15 Song et al 7 second-order slip model 16 "helium and nitrogen," "200 mm wide," "silicon and glass walls" Li et al 13 second-order slip model 17 Yin et al 14 second-order slip model kerogen, indicating that the diffusion capacity of each component is similar, no matter in the mixture or pure conditions; Collell et al 41 simulated the transport process of the multicomponent hydrocarbon mixture in shale organic matter and proposed a simple scaling law to predict the diffusion coefficient of linear alkanes; He et al 42 presented a MD simulation on the gas diffusion phenomenon in the kerogen matrix to measure the tortuosity of the kerogen structure. Evidently, the second strategy is more appropriate to the realistic physical structure of organic shale.…”

Section: Introductionmentioning

confidence: 99%

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Roughness Factor-Dependent Transport Characteristic of Shale Gas through Amorphous Kerogen Nanopores

Fan

et al. 2020

J. Phys. Chem. C

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In the past decades, shale gas has been recognized as the promising unconventional resource for global energy storage, and a clear understanding of the gas-transport characteristic within nonporous shale organic matter (i.e., kerogen) is fundamental for the effective development of shale reservoirs. In this regard, previous studies were generally conducted based on the ideally smooth nanochannels (e.g., graphite slit or tube) without considering the atomistic-scale roughness of the walls. Herein, using molecular dynamics (MD) simulations, we perform a systematical investigation on the gas-transport characteristic through amorphous organic nanopores constructed by realistic kerogen molecules. The results show that the gas-transport velocity in amorphous organic nanopores drops dramatically (40, 70, and 90%) only with tiny roughness factors (0.3, 0.6, and 1.2%) when compared with ideally smooth nanochannels. Further analysis of the potential energy surface and the particle trajectory justifies the entirely different gas-transport mechanisms in ideally smooth (surface diffusion) and relative rough (viscosity diffusion) organic nanopores. Besides, based on the insights of numerous MD simulations (pore sizes: 3−9 nm and system pressures: 5−50 MPa), a new analytical model that is able to consider the key effect of roughness factor on gas transport in organic-rich shale is developed, which is well verified with the experimental results. It is particularly found that the gas-transport capacity in organic-rich shale (∼1 nm of slippage length) would be enormously overrated as much as 2 orders of magnitude by the traditional cognition based on ideally smooth nanopores (∼100 nm of slippage length).

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“…3. Based on the parallel capillary model, many permeability models (Li et al , 2018Cai et al 2018;Wu et al 2020) are successfully proposed to estimate the permeability of porous media. In the capillary model, the micropores are assumed as a bundle of tortuous paralleled capillaries and the microfractures are assumed as a bundle of tortuous paralleled rectangular channels.…”

Section: Fractal Theory Of Dual-porosity Media Of Cbm Reservoirsmentioning

confidence: 99%

A Fractal Permeability Model for Gas Transport in the Dual-Porosity Media of the Coalbed Methane Reservoir

et al. 2021

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In the process of coalbed methane (CBM) exploitation, permeability is a key controlling parameter for gas transport in the CBM reservoirs. The CBM reservoir contains a large number of micropores and microfractures with complex structures. In order to accurately predict the gas permeability of the micropores and microfractures in CBM reservoirs, a fractal permeability model was developed in this work. This model considers the comprehensive effects of real gas, stress dependence, multiple gas flow mechanisms (e.g., slip flow, Knudsen diffusion and surface diffusion) and fractal characteristics (e.g., pore size distribution and flow path tortuosity) of micropores and microfractures on the gas permeability. Then, this fractal permeability model was verified by the reliable experimental data and other theoretical models. Finally, the sensitivity analysis is conducted to identify key factors to the permeability of CBM reservoir. The results showed that the fractal characteristics of the micropores and microfractures have significant effects on the permeability of CBM reservoir. Higher fractal dimension of micropores diameter and microfractures aperture represents the larger number of micropores and microfractures, resulting in a higher permeability. Higher tortuosity fractal dimension of micropores and microfractures means higher gas flow resistance, leading to the lower permeability. The multiple gas transport mechanisms coexist in micropores and microfractures of CBM reservoir. The permeability of slip flow and Knudsen diffusion both increases with the decrease in pore pressure. Surface diffusion is an important gas transport mechanisms in micropores, but it can be ignored in the microfractures. Knudsen diffusion plays a more obvious role in the lower pore pressure, which controls the gas transport in microfractures. And microfractures are beneficial to improve gas transport capacity of coalbed methane reservoir.

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Fractal-based real gas flow model in shales: An interplay of nano-pore and nano-fracture networks

Cited by 36 publications

References 61 publications

Transport of Shale Gas in Microporous/Nanoporous Media: Molecular to Pore-Scale Simulations

Transport of Shale Gas in Microporous/Nanoporous Media: Molecular to Pore-Scale Simulations

Roughness Factor-Dependent Transport Characteristic of Shale Gas through Amorphous Kerogen Nanopores

A Fractal Permeability Model for Gas Transport in the Dual-Porosity Media of the Coalbed Methane Reservoir

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