Pore‐Scale Visualization of Methane Hydrate‐Bearing Sediments With Micro‐CT

Lei, Liang; Seol, Yongkoo; Jarvis, Karl

doi:10.1029/2018gl078507

Cited by 95 publications

(71 citation statements)

References 35 publications

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“…This leads to the grayscale level of methane hydrate in Figure c lying in the middle position between grayscale levels of methane gas and NaCl solution. This kind of grayscale level distribution for methane gas, methane hydrate, and solution is quite consistent with those reported by Lei et al () and Li et al ().…”

Section: Theory and Experimental Methodssupporting

confidence: 92%

“…The bulk porosity of A‐graded and B‐graded host sands is controlled between 37% and 38%, and the initial water saturation is about 0.5. For reference, various kinds of solutions used as alternatives to pure water can keep enhancing the phase contrast between hydrate and solution in X‐ray CT images during hydrate formation due to the increasing solute concentration (Chen et al, ; Kerkar et al, ; Lei et al, ; Li et al, ; Ta et al, ).…”

Section: Theory and Experimental Methodsmentioning

confidence: 99%

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Pore Fractal Characteristics of Hydrate‐Bearing Sands and Implications to the Saturated Water Permeability

Zhang

Ning

et al. 2020

JGR Solid Earth

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Permeability mainly governs fluid flow through hydrate‐bearing sediments, and its theoretical models play a primary role in the efficiency prediction of gas recovery from hydrate reservoirs by using numerical simulators. Most of these numerical simulators rely on empirical or semiempirical permeability models largely due to the lack of suitable parameters that well quantify the evolution of pore structures. In this study, X‐ray computed tomography scans are conducted on methane hydrate‐bearing sands, followed by extractions of the maximal diameter and fractal dimensions for the pore space occupied by fluids. These extracted parameters, including area and volume pore‐size fractal dimensions, tortuosity fractal dimension, and the area maximal pore diameter, are further extended to develop fractal theory‐based models for predictions of the hydraulic tortuosity and the saturated water permeability in hydrate‐bearing sands. Results show that the pore space occupied by fluids within hydrate‐bearing sands is inherently fractal. The area pore‐size fractal dimension decreases but the tortuosity fractal dimension changes little with increasing hydrate saturation, and the sum of these two fractal dimensions can be used to predict the volume pore‐size fractal dimension. In addition, the area maximal pore diameter decreases with increasing hydrate saturation, and a semiempirical model is proposed. The fractal theory‐based permeability reduction model agrees well with available experimental data, and it can capture the essential physics of saturated water permeability reduction in hydrate‐bearing sediments during hydrate formation.

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Section: Theory and Experimental Methodssupporting

confidence: 92%

Section: Theory and Experimental Methodsmentioning

confidence: 99%

Pore Fractal Characteristics of Hydrate‐Bearing Sands and Implications to the Saturated Water Permeability

Zhang

Ning

et al. 2020

JGR Solid Earth

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“…They concluded that all the resultant images showed a water film between hydrate and sand. However, Lei et al () got an opposite conclusion by using phase‐contrast CT in their study. They developed a new imaging method for distinguishing methane hydrate from water and found that a low density thin layer on the surface of sand particles is more likely to be caused by diffraction rather than a real water layer.…”

Section: Introductionmentioning

confidence: 83%

“…They developed a new imaging method for distinguishing methane hydrate from water and found that a low density thin layer on the surface of sand particles is more likely to be caused by diffraction rather than a real water layer. Whether there is a water layer between hydrate and sand particles is still controversial (Lei et al, ; Sell et al, ). In view of the water film, gray value curves of CT image were helpful to identify the boundaries between hydrates and quartz sands (Hu et al, ).…”

Section: Introductionmentioning

confidence: 99%

Investigation on the Multiparameter of Hydrate‐Bearing Sands Using Nano‐Focus X‐Ray Computed Tomography

Liu

et al. 2019

JGR Solid Earth

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In this study, a nano‐focus X‐ray computed tomography (X‐CT) is used to observe the formation of methane hydrate in sands on pore scale and to quantify hydrate saturation, pore structure parameters, and permeability of hydrate‐bearing sands. A new analytical technique is developed to improve the identification of water‐hydrate boundary. Three hydrate accumulation habits (i.e., floating, contacting, and cementing) in pore spaces are observed. When there is no methane bubble, hydrate distribution evolves from floating to contacting and then to cementing as hydrate saturation increases. In contrast, only contacting and cementing distribution patterns appear in the pores with methane bubbles. Based on the surface extraction and defect detection from 3‐D images, both the gas/water/hydrate distributions and the pore structure characteristics are investigated. The results show that the porosity, the maximal pore volume, and maximal diameter decrease as hydrates accumulate in the pores. However, the maximal pore surface, the total pore number, and the large pores (>100 voxels) number increase gradually until the hydrate saturation reaches 35%, when they turn to decrease rapidly. The pore structure parameters show detailed changes of hydrate and water on pore scale. The incompressible Navier‐Stokes equations are used to calculate absolute permeability of hydrate‐bearing sands based on X‐ray computed tomography digital images. It indicates that the microdistribution of the hydrate has a significant effect on the permeability calculation. The fluid streamlines obtained through simulation are used to track the water transport paths.

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“…Similarly, Phillips et al (2019) and Santamarina et al (2015) suggest that local freshening at the pore scale has a first-order control on dissociation. Recent micro-CT work by Lei et al (2018) has directly observed hydrate formation in pores and associated changes in salinity. Microfluidics (e.g., Kang et al, 2016;Martinez de Baños et al, 2015) and micro-Raman (e.g., Davies et al, 2010;Prasad et al, 2009) experiments have visually investigated and analyzed the dynamic processes of hydrate formation and dissociation.…”

Section: Future Studies To Illuminate How Hydrate Systems Formmentioning

confidence: 99%

Mechanisms of Methane Hydrate Formation in Geological Systems

You

Flemings

Malinverno

et al. 2019

Reviews of Geophysics

147

110

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Natural gas hydrate is ice‐like mixture of gas (mostly methane) and water that is widely found in sediments along the world's continental margins and within and beneath permafrost and glaciers in a near‐surface depth interval where the pressure is sufficiently high and temperature sufficiently low for gas hydrate to be stable. We categorize the myriad of geological gas hydrate deposits into five characteristic types. We then review the multiple quantitative models that have proposed to describe the genesis of these deposits and describe how each may have formed. We emphasize the importance of coupling multiphase flow (free gas and liquid water) and multicomponent reactive transport with geological history to describe the dynamical processes of gas hydrate formation and evolution in geological systems. A better insight into the kinetics of methane formation from microbial biogenesis and the processes of multiphase flow at the pore scale will advance our knowledge of how these systems form. By understanding the generation and evolution of gas hydrate through time, we will better decipher the role of gas hydrate in the carbon cycle, its potential to contribute to climate change and geohazards, and how to design optimal strategies for gas production from hydrate reservoirs.

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Pore‐Scale Visualization of Methane Hydrate‐Bearing Sediments With Micro‐CT

Cited by 95 publications

References 35 publications

Pore Fractal Characteristics of Hydrate‐Bearing Sands and Implications to the Saturated Water Permeability

Pore Fractal Characteristics of Hydrate‐Bearing Sands and Implications to the Saturated Water Permeability

Investigation on the Multiparameter of Hydrate‐Bearing Sands Using Nano‐Focus X‐Ray Computed Tomography

Mechanisms of Methane Hydrate Formation in Geological Systems

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