Multi-scale Analysis of Gas Transport Mechanisms in Kerogen

Kou, Rui; Alafnan, Saad; Akkutlu, I. Yücel

doi:10.1007/s11242-016-0787-7

Cited by 62 publications

(33 citation statements)

References 31 publications

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“…In this study, the tortuosity is defined as the ratio of the length of the path and the distance between its ends along z-axis [52] (Figure 14). Specific surface area (the surface area per bulk unit volume) and tortuosity are important macroscopic pore structure parameters of porous material [48][49][50], which can reflect structural properties of the cracks in shale [51]. In this study, the tortuosity is defined as the ratio of the length of the path and the distance between its ends along z-axis [52] (Figure 14).…”

Section: Quantitative Characterization Of Cracksmentioning

confidence: 99%

Mechanical Property Measurements and Fracture Propagation Analysis of Longmaxi Shale by Micro-CT Uniaxial Compression

et al. 2018

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The mechanical properties and fracture propagation of Longmaxi shale loading under uniaxial compression were measured using eight cylindrical shale specimens (4 mm in diameter and 8 mm in height), with the bedding plane oriented at 0 • and 90 • to the axial loading direction, respectively, by micro computed tomography (micro-CT). Based on the reconstructed three-dimensional (3-D) CT images of cracks, different stages of the crack growth process in the 0 • and 90 • orientation specimen were revealed. The initial crack generally occurred at relatively smaller loading force in the 0 • bedding direction specimen, mainly in the form of tensile splitting along weak bedding planes. Shear sliding fractures were dominant in the specimens oriented at 90 • , with a small number of parallel cracks occurring on the bedding plane. The average thickness and volume of cracks in the 90 • specimen is higher than those for the specimen oriented at 0 • . The geometrical characterization of fractures segmented from CT scan binary images shows that a specific surface area correlates with tortuosity at the different load stages of each specimen. The 3-D box-counting dimension (BCD) calculations can accurately reflect crack evolution law in the shale. The results indicate that the cracks have a more complex pattern and rough surface at an orientation of 90 • , due to crossed secondary cracks and shear failure.Various experimental methods, e.g., electromagnetic radiation (EMR), acoustic emission (AE), micro-seismic (MS), infrared technique, high speed digital imaging, and computerized tomography (CT), have been used to analyze the mechanical behavior of rocks (including shale) during uniaxial or triaxial loading [15][16][17][18][19][20][21]. CT scanning has been widely applied in the investigation of damage propagation since 1997, due to the three-dimensional (3-D) visualization and high-resolution imaging [22][23][24][25][26][27][28]. Kawakata et al. used CT to study the initial mesoscopic damage characteristics of rock materials, and observed spatial fault development in granite undergoing compression [29,30]. In the experiment, only the damaged specimens, rather than the entire process from crack initiation to specimen destruction, were scanned, and then observed by 3-D reconstruction of X-ray CT images. To examine the entire process, Ge et al. investigated rock compression with a real-time CT test [23]. Through the use of the industrial CT images, the rock meso-damage propagation law was revealed. Rock failure started with micro-pore and micro-crack compression, growth, bifurcation, and development, followed by fracture. Sun et al. displayed real-time deformation in backfill body under loading using industrial CT in several slices, and provided insights into the process of faulting [31]. However, the relatively low spatial resolution and image quality of conventional industrial CT is not suitable for fine-grained rocks. Furthermore, the 3-D information was not fully captured or used, which limited the accuracy of further calculation ...

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Section: Quantitative Characterization Of Cracksmentioning

confidence: 99%

Mechanical Property Measurements and Fracture Propagation Analysis of Longmaxi Shale by Micro-CT Uniaxial Compression

et al. 2018

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“…Recently, mathematical models capturing the key features of gas flow in all four regimes have been developed in the case of gas flow through a single cylindrical tube [e.g., Beskok and Karniadakis , ; Javadpour , ; Kou et al , ]. In a pioneering study, Klinkenberg [] experimentally studied the transport of gas through rocks in the slip flow regime and showed that the apparent permeability to gas is a function of the inverse of the mean gas pressure, k app = k ∞ (1 + b /< p >), where k ∞ is seemingly equal to the liquid permeability, b is the gas slippage correction factor, and < p > is the mean gas pressure.…”

Section: Introductionmentioning

confidence: 99%

“…Surprisingly, (z-z c ) had a very weak effect on the ratio of the apparent gas permeability to the absolute liquid permeability, k app /k abs , suggesting that the Klinkenberg gas slippage correction factor is nearly independent of connectivity. We constructed models of k app and k app /k abs based on the observed power law and tested them by comparison with published experimental data on glass beads and other materials.Recently, mathematical models capturing the key features of gas flow in all four regimes have been developed in the case of gas flow through a single cylindrical tube [e.g., Beskok and Karniadakis, 1999;Javadpour, 2009;Kou et al, 2017]. In a pioneering study, Klinkenberg [1941] experimentally studied the LI ET AL.…”

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confidence: 99%

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Percolation connectivity, pore size, and gas apparent permeability: Network simulations and comparison to experimental data

Tang

Bernabé

et al. 2017

JGR Solid Earth

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We modeled single‐phase gas flow through porous media using percolation networks. Gas permeability is different from liquid permeability. The latter is only related to the geometry and topology of the pore space, while the former depends on the specific gas considered and varies with gas pressure. As gas pressure decreases, four flow regimes can be distinguished as viscous flow, slip flow, transition flow, and free molecular diffusion. Here we use a published conductance model presumably capable of predicting the flow rate of an arbitrary gas through a cylindrical pipe in the four regimes. We incorporated this model into pipe network simulations. We considered 3‐D simple cubic, body‐centered cubic, and face‐centered cubic lattices, in which we varied the pipe radius distribution and the bond coordination number. Gas flow was simulated at different gas pressures. The simulation results showed that the gas apparent permeability kapp obeys an identical scaling law in all three lattices, kapp ~ (z‐zc)β, where the exponent β depends on the width of the pipe radius distribution, z is the mean coordination number, and zc its critical value at the percolation threshold. Surprisingly, (z‐zc) had a very weak effect on the ratio of the apparent gas permeability to the absolute liquid permeability, kapp/kabs, suggesting that the Klinkenberg gas slippage correction factor is nearly independent of connectivity. We constructed models of kapp and kapp/kabs based on the observed power law and tested them by comparison with published experimental data on glass beads and other materials.

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“…Some researchers have attempted to introduce an apparent permeability coefficient to correct the HP equation (Islam and Patzek, 2014;. We noticed that shale gas flow in roughened nanopores exhibited a parabolic velocity profile, which is a distinct characteristic of viscous flow (Kou et al, 2016). According to previous studies, the flow model still belongs to the slip flow region Yao et al, 2013).…”

Section: Flow Characterizationmentioning

confidence: 99%

Molecular dynamics simulation of methane transport in confined organic nanopores with high relative roughness

Kulasinski

Zheng

et al. 2019

Journal of Natural Gas Science and Engineering

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Understanding and characterizing the transport of shale gas (methane) through the nanopores of kerogens are critical for the accurate prediction of shale gas recovery. However, the key factors that regulate shale gas transport through highly roughened nanopores of shale kerogens are not fully understood. In this work, methane transport in organic nanopores with a high relative roughness is characterized using equilibrium and nonequilibrium molecular dynamics methods. According to our results, the CH 4 mass flux has a linear relationship with the pressure gradient, consistent with previous studies, while the calculated slip lengths and gas fluxes varied with different roughness geometries in the order of sigmoidal ≥ triangular > rectangular. Surface slip flow can be a major contributor to the overall gas flux, but surprisingly, the relative contribution of surface slip flow is independent of the pressure gradient. In contrast, the contributions of both slip flow and the average gas fluxes vary strongly with pore diameters. Typical contributions of the adsorbed layer to the overall gas flux are in the range 20-40% but vary from as high as 74% in a 4-nm pore to as low as 6% in a 16-nm pore. Compared to smooth nanopores, we find that, in nanopores with realistically high degrees of relative roughness, methane confinement in cavities decouples slip flow from the flow in the pore interior, significantly reducing the overall flux.

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Multi-scale Analysis of Gas Transport Mechanisms in Kerogen

Cited by 62 publications

References 31 publications

Mechanical Property Measurements and Fracture Propagation Analysis of Longmaxi Shale by Micro-CT Uniaxial Compression

Mechanical Property Measurements and Fracture Propagation Analysis of Longmaxi Shale by Micro-CT Uniaxial Compression

Percolation connectivity, pore size, and gas apparent permeability: Network simulations and comparison to experimental data

Molecular dynamics simulation of methane transport in confined organic nanopores with high relative roughness

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