Pore-scale analysis of coal cleat network evolution through liquid nitrogen treatment: A Micro-Computed Tomography investigation

Abstract A pore-scale numerical simulation was carried out in this study to predict the natural convection in a cubic cavity filled with reconstructed porous medium using lattice Boltzmann Method (LBM). The computational porous domain was established with the micro-computed tomography technique. The natural convection phenomena were predicted with the pore-scale simulation for different thermal boundary conditions and fluid thermal properties. The results show that the natural convection in the present porous domain is more obvious as the side wall is heated compared to that as the bottom wall is heated. The existence of porous structure suppresses the natural convection in the cubic cavity. As Rayleigh number increases, the natural convection in the porous domain is enhanced accordingly. The heat flux distribution on the porous structure surface varies intensively due to the complex flow characteristic in the small pore spaces. The numerical approach presented in this study is to provide a promising solution that can simulate pore-scale natural convection in porous medium and can be further extended for the development of field-scale model for transport processes in porous medium.

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Fast micro-computed tomography data of solute transport in porous media with different heterogeneity levels

Scientific Data ◽

10.1038/s41597-021-00803-3 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Stefanie Van Offenwert ◽

Veerle Cnudde ◽

Marijn Boone ◽

Tom Bultreys

Keyword(s):

Computed Tomography ◽

Solute Transport ◽

Temporal Resolution ◽

Solute Concentration ◽

Transport Processes ◽

Pore Scale ◽

Micro Computed Tomography ◽

Tracer Injection ◽

Voxel Size ◽

Scale Heterogeneity

AbstractSolute transport processes are influenced by pore-scale heterogeneity. To study this, transient micron-scale solute concentration fields were imaged by fast laboratory-based X-ray micro-computed tomography. We performed tracer injection experiments in three types of porous material with increasing levels of heterogeneity (sintered glass, Bentheimer sandstone and Savonnières limestone). Different Peclet numbers were used during the experiments. For each sample and Peclet number, datasets of 40 to 74 3D images were acquired by continuous scanning with a voxel size of 13.4 to 14.6 µm and a temporal resolution of 15 to 12 seconds. To determine the measurement uncertainty on the obtained concentration fields, we performed calibration experiments under similar circumstances (temporal resolution of 12 seconds and voxel size of 13.0 µm). Here, we provide a systematic description of the data acquisition and processing and make all data, a total of 464 tomograms, publicly available. The combined dataset offers new opportunities to study the influence of pore-scale heterogeneity on solute transport, and to validate pore-scale simulations of this process in increasingly complex samples.

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Coal fracturing through liquid nitrogen treatment: a micro-computed tomography study

The APPEA Journal ◽

10.1071/aj19105 ◽

2020 ◽

Vol 60 (1) ◽

pp. 67

Author(s):

Hamed Akhondzadeh ◽

Alireza Keshavarz ◽

Faisal Ur Rahman Awan ◽

Ahmed Z. Al-Yaseri ◽

Stefan Iglauer ◽

...

Keyword(s):

Computed Tomography ◽

Liquid Nitrogen ◽

Coalbed Methane ◽

Network Connectivity ◽

Cylindrical Sample ◽

Morphological Alteration ◽

3D Analysis ◽

Micro Computed Tomography ◽

Rock Compressibility ◽

Coalbed Methane Production

Low permeability of coal has been a constant obstacle to economic production from coalbed methane reservoirs, and liquid nitrogen (LN2) treatment has been investigated as one approach to address this issue. This study examined LN2 fracturing of a bituminous coal at pore-scale through 3D X-ray micro-computed tomography. For this purpose, a cylindrical sample was immersed into LN2 for 60 min. The micro-CT results clearly showed that the rapid freezing of the coal with LN2 generated fracture planes with large apertures originating from the pre-existing cleats in the rock. This treatment also connected original cleats with originally isolated pores and micro-cleats, thereby increasing pore network connectivity. Moreover, scanning electron microscopy highlighted the appearance of continuous wide conductive fractures with a maximum opening size of 9 µm. Furthermore, a nano-indentation technique was used to test the effect of LN2 on coal mechanical properties. The indentation moduli decreased by up to 14%, which was attributed to the increase in the cracked rock compressibility, showing considerable fracturing efficiency of the LN2 treatment. Through in-situ microscopic visualisation and surface investigation, this study quantified the pore structure and connectivity evolution of the rock based on the morphological alteration, and demonstrated the promising effect of LN2 freezing on fracturing of bituminous coals, thus aiding coalbed methane production. The significance of this study was investigating the mechanisms associated with and the efficiency of LN2 treatment of a coal rock in a 3D analysis inside the rock.

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Micro-computed tomography pore-scale study of flow in porous media: Effect of voxel resolution

Advances in Water Resources ◽

10.1016/j.advwatres.2015.07.012 ◽

2016 ◽

Vol 95 ◽

pp. 276-287 ◽

Cited By ~ 64

Author(s):

S.M. Shah ◽

F. Gray ◽

J.P. Crawshaw ◽

E.S. Boek

Keyword(s):

Computed Tomography ◽

Porous Media ◽

Flow In Porous Media ◽

Pore Scale ◽

Media Effect ◽

Micro Computed Tomography

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Visualized Experiments on Residual Oil Classification and Its Influencing Factors in Waterflooding Using Micro-Computed Tomography

Journal of Energy Resources Technology ◽

10.1115/1.4045926 ◽

2020 ◽

Vol 142 (8) ◽

Cited By ~ 4

Author(s):

Rui Song ◽

Jiajun Peng ◽

Shuyu Sun ◽

Yao Wang ◽

Mengmeng Cui ◽

...

Keyword(s):

Computed Tomography ◽

Shape Factor ◽

Euler Number ◽

Contact Angles ◽

Pore Geometry ◽

Pore Scale ◽

Residual Oil ◽

Micro Computed Tomography ◽

Two Samples ◽

Oil Water

Abstract Pore-scale mechanism of the waterflooding process contributes to enhanced oil recovery, which has been widely emphasized in the petroleum industry. In this paper, pore-scale waterflooding experiments are carried out on mixed-wetted natural sandstone and 3D printed sandstone using micro-computed tomography (μ-CT). The high-resolution images of oil/water distribution in different stages of waterflooding cycles are acquired. The classification of residual oil after waterflooding is conducted using the shape factor and Euler number, which represents the shape and spatial connectivity, respectively. The in situ contact angles are measured on the segmented images and the pore-scale wettability of these two samples is analyzed. Then, the effects of pore structure, micro-fracture and wettability on the distribution of the patterns of residual oil are analyzed. The results indicate that the types of isolated, cluster, network, and film (only for natural sample) are the main forms of residual oil patterns after the waterflooding process. The negative correlation between the shape factor and the Euler number of the typical oil blocks are presented. The effect of wettability and pore geometry on the morphology of the oil/water interface is quantitatively studied. The capillary pressure is the key factor for the formation of the residual oil blocks, the morphology of which is controlled by both wettability and pore geometry.

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