Research

17 pages, 5796 KiB

Open AccessArticle

Natural Gas Reservoir Characteristics and Non-Darcy Flow in Low-Permeability Sandstone Reservoir of Sulige Gas Field, Ordos Basin

by Xiaoying Lin, Jianhui Zeng, Jian Wang and Meixin Huang

Energies 2020, 13(7), 1774; https://doi.org/10.3390/en13071774 - 07 Apr 2020

Cited by 7 | Viewed by 2715

Abstract

In order to reveal the gas–water distribution and formation mechanism of the low-permeability sandstone gas reservoir, the gas reservoir distribution and the formation mechanism in a low-permeability sandstone gas reservoir are investigated using data obtained from a physical simulation experiment of gas percolation. [...] Read more.

In order to reveal the gas–water distribution and formation mechanism of the low-permeability sandstone gas reservoir, the gas reservoir distribution and the formation mechanism in a low-permeability sandstone gas reservoir are investigated using data obtained from a physical simulation experiment of gas percolation. The exploration and experimenting for petroleum in the upper Paleozoic gas pool of the Sulige gas field in the Ordos basin in this paper. Results showed that the gas reservoir is characterized by low gas saturation, a complex distribution relationship of gas–water, and weak gas–water gravity differentiation. The characteristics of gas distribution are closely related to permeability, gas flow, and migration force. The capillary pressure difference is the main driving force of gas accumulation. There exists a threshold pressure gradient as gas flows in low-permeability sandstone. The lower that permeability, the greater the threshold pressure gradient. When the driving force cannot overcome the threshold pressure (minimal resistance), the main means of gas migration is diffusion; when the driving force is between minimal and maximal resistance, gas migrates with non-Darcy flow; when the driving force is greater than maximal resistance, gas migrates with Darcy flow. The complex gas migration way leads to complicated gas- water distribution relationship. With the same driving force, gas saturation increases with the improvement of permeability, thus when permeability is greater than 0.15 × 10⁻³ µ m², gas saturation could be greater than 50%. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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10 pages, 1200 KiB

Open AccessArticle

Relative Pressure Drop Model for Hydrate Formation and Transportability in Flowlines in High Water Cut Systems

by Trung-Kien Pham, Ana Cameirao, Aline Melchuna, Jean-Michel Herri and Philippe Glénat

Energies 2020, 13(3), 686; https://doi.org/10.3390/en13030686 - 05 Feb 2020

Cited by 6 | Viewed by 2478

Abstract

Today, oil and gas fields gradually become mature with a high amount of water being produced (water cut (WC)), favoring conditions for gas hydrate formation up to the blockage of pipelines. The pressure drop is an important parameter which is closely related to [...] Read more.

Today, oil and gas fields gradually become mature with a high amount of water being produced (water cut (WC)), favoring conditions for gas hydrate formation up to the blockage of pipelines. The pressure drop is an important parameter which is closely related to the multiphase flow characteristics, risk of plugging and security of flowlines. This study developed a model based on flowloop experiments to predict the relative pressure drop in pipelines once hydrate is formed in high water cutsystems in the absence and presence of AA-LDHI and/or salt. In this model, the relative pressure drop during flow is a function of hydrate volume and hydrate agglomerate structure, represented by the volume fraction factor (K_v). This parameter is adjusted for each experiment between 1.00 and 2.74. The structure of the hydrate agglomerates can be predicted from the measured relative pressure drop as well as their impact on the flow, especially in case of a homogeneous suspension of hydrates in the flow. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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29 pages, 2132 KiB

Open AccessArticle

An All-At-Once Newton Strategy for Marine Methane Hydrate Reservoir Models

by Shubhangi Gupta, Barbara Wohlmuth and Matthias Haeckel

Energies 2020, 13(2), 503; https://doi.org/10.3390/en13020503 - 20 Jan 2020

Cited by 9 | Viewed by 2976

Abstract

The migration of methane through the gas hydrate stability zone (GHSZ) in the marine subsurface is characterized by highly dynamic reactive transport processes coupled to thermodynamic phase transitions between solid gas hydrates, free methane gas, and dissolved methane in the aqueous phase. The [...] Read more.

The migration of methane through the gas hydrate stability zone (GHSZ) in the marine subsurface is characterized by highly dynamic reactive transport processes coupled to thermodynamic phase transitions between solid gas hydrates, free methane gas, and dissolved methane in the aqueous phase. The marine subsurface is essentially a water-saturated porous medium where the thermodynamic instability of the hydrate phase can cause free gas pockets to appear and disappear locally, causing the model to degenerate. This poses serious convergence issues for the general-purpose nonlinear solvers (e.g., standard Newton), and often leads to extremely small time-step sizes. The convergence problem is particularly severe when the rate of hydrate phase change is much lower than the rate of gas dissolution. In order to overcome this numerical challenge, we have developed an all-at-once Newton scheme tailored to our gas hydrate model, which can handle rate-based hydrate phase change coupled with equilibrium gas dissolution in a mathematically consistent and robust manner. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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14 pages, 8811 KiB

Open AccessArticle

Experimental Investigation of Spontaneous Imbibition of Water into Hydrate Sediments Using Nuclear Magnetic Resonance Method

by Liu Yang, Chuanqing Zhang, Jianchao Cai and Hongfeng Lu

Energies 2020, 13(2), 445; https://doi.org/10.3390/en13020445 - 16 Jan 2020

Cited by 10 | Viewed by 1996

Abstract

Field observations show that less than one percent of dissociation water can be produced during gas hydrate production, resulting from spontaneous water imbibition into matrix pores. What’s more, the hydrate sediments are easily dispersed in water, and it is difficult to carry out [...] Read more.

Field observations show that less than one percent of dissociation water can be produced during gas hydrate production, resulting from spontaneous water imbibition into matrix pores. What’s more, the hydrate sediments are easily dispersed in water, and it is difficult to carry out spontaneous imbibition experiments. At present, there is little research work on the imbibition capacity of hydrate sediments. In this paper, a new method of water imbibition is proposed for hydrate sediments, and nuclear magnetic resonance (NMR) technique is used to monitor water migration. The results show that as the imbibition time increases, the water is gradually imbibed into matrix pores. Water imbibition can cause dramatic changes in pore structure, such as microfracture initiation, fracture network generation and skeleton dispersion. When the imbibition time exceeds a critical value, many secondary pores (new large pores and micro-fractures) start to appear. When imbibition time exceeds the dispersion time, fracture networks are generated, eventually leading to dispersion of the sediment skeleton. The imbibition curves of hydrate sediments can be divided into two linear stages, which corresponds, respectively, to water imbibition of primary pores and secondary pores. The imbibition rate of secondary pores is significantly larger than that of primary pores, indicating that the generation of new fractures can greatly accelerate the imbibition rate. Research on the characteristics of water imbibition in hydrate sediments is important for optimizing hydrate production regime and increasing natural gas production. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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11 pages, 1388 KiB

Open AccessArticle

Sensitivity Analysis of Rock Electrical Influencing Factors of Natural Gas Hydrate Reservoir in Permafrost Region of Qilian Mountain, China

by Zhenzhou Lin, Huaimin Dong, Hui Fang, Jianmeng Sun and Xiaojiang Wang

Energies 2019, 12(23), 4592; https://doi.org/10.3390/en12234592 - 03 Dec 2019

Cited by 3 | Viewed by 2631

Abstract

It has been found that the relatively low abundance of gas hydrate in the Muli area of the Qilian Mountain causes gas hydrate reservoirs to have low-resistivity characteristics similar to those of low-resistivity oil and gas reservoirs. Therefore, it has great significance to [...] Read more.

It has been found that the relatively low abundance of gas hydrate in the Muli area of the Qilian Mountain causes gas hydrate reservoirs to have low-resistivity characteristics similar to those of low-resistivity oil and gas reservoirs. Therefore, it has great significance to research the main controlling factors affecting the electrical properties, and then come up a new logging identification and evaluation model for low-resistivity gas hydrate reservoirs. In this investigation, the rock samples of sandstone from gas hydrate reservoirs were scanned by CT and combined with gas hydrate distribution characteristics. The three-dimensional digital rocks with different hydrate saturation were constructed using the diffusion limited aggregation (DLA) model, and the resistivity was simulated via the finite element method. After sorting out the influencing factors of electrical characteristics, the sensitivity of the factors affecting electrical properties was evaluated using orthogonal analysis, using variance analysis and trend analysis to quantitatively evaluate the influencing factors of rock electrical sensitivity, so as to distinguish the main and secondary factors affecting rock electrical sensitivity. The results show that the sensitivity of rock electrical properties to the six influencing factors from strong to weak are: formation water salinity, water film thickness, shale content, conductive mineral content, micropores, and average coordination number. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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24 pages, 3674 KiB

Open AccessArticle

Thermal State of the Blake Ridge Gas Hydrate Stability Zone (GHSZ)—Insights on Gas Hydrate Dynamics from a New Multi-Phase Numerical Model

by Ewa Burwicz and Lars Rüpke

Energies 2019, 12(17), 3403; https://doi.org/10.3390/en12173403 - 03 Sep 2019

Cited by 14 | Viewed by 3580

Abstract

Marine sediments of the Blake Ridge province exhibit clearly defined geophysical indications for the presence of gas hydrates and a free gas phase. Despite being one of the world’s best-studied gas hydrate provinces and having been drilled during Ocean Drilling Program (ODP) Leg [...] Read more.

Marine sediments of the Blake Ridge province exhibit clearly defined geophysical indications for the presence of gas hydrates and a free gas phase. Despite being one of the world’s best-studied gas hydrate provinces and having been drilled during Ocean Drilling Program (ODP) Leg 164, discrepancies between previous model predictions and reported chemical profiles as well as hydrate concentrations result in uncertainty regarding methane sources and a possible co-existence between hydrates and free gas near the base of the gas hydrate stability zone (GHSZ). Here, by using a new multi-phase finite element (FE) numerical model, we investigate different scenarios of gas hydrate formation from both single and mixed methane sources (in-situ biogenic formation and a deep methane flux). Moreover, we explore the evolution of the GHSZ base for the past 10 Myr using reconstructed sedimentation rates and non-steady-state P-T solutions. We conclude that (1) the present-day base of the GHSZ predicted by our model is located at the depth of ~450 mbsf, thereby resolving a previously reported inconsistency between the location of the BSR at ODP Site 997 and the theoretical base of the GHSZ in the Blake Ridge region, (2) a single in-situ methane source results in a good fit between the simulated and measured geochemical profiles including the anaerobic oxidation of methane (AOM) zone, and (3) previously suggested 4 vol.%–7 vol.% gas hydrate concentrations would require a deep methane flux of ~170 mM (corresponds to the mass of methane flux of 1.6 × 10⁻¹¹ kg s⁻¹ m⁻²) in addition to methane generated in-situ by organic carbon (POC) degradation at the cost of deteriorating the fit between observed and modelled geochemical profiles. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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14 pages, 7066 KiB

Open AccessArticle

Magnetic Resonance Imaging of Methane Hydrate Formation and Dissociation in Sandstone with Dual Water Saturation

by Stian Almenningen, Per Fotland and Geir Ersland

Energies 2019, 12(17), 3231; https://doi.org/10.3390/en12173231 - 22 Aug 2019

Cited by 6 | Viewed by 2478

Abstract

This paper reports formation and dissociation patterns of methane hydrate in sandstone. Magnetic resonance imaging spatially resolved hydrate growth patterns and liberation of water during dissociation. A stacked core set-up using Bentheim sandstone with dual water saturation was designed to investigate the effect [...] Read more.

This paper reports formation and dissociation patterns of methane hydrate in sandstone. Magnetic resonance imaging spatially resolved hydrate growth patterns and liberation of water during dissociation. A stacked core set-up using Bentheim sandstone with dual water saturation was designed to investigate the effect of initial water saturation on hydrate phase transitions. The growth of methane hydrate (P = 8.3 MPa, T = 1–3 °C) was more prominent in high water saturation regions and resulted in a heterogeneous hydrate saturation controlled by the initial water distribution. The change in transverse relaxation time constant, T₂, was spatially mapped during growth and showed different response depending on the initial water saturation. T₂ decreased significantly during growth in high water saturation regions and remained unchanged during growth in low water saturation regions. Pressure depletion from one end of the core induced a hydrate dissociation front starting at the depletion side and moving through the core as production continued. The final saturation of water after hydrate dissociation was more uniform than the initial water saturation, demonstrating the significant redistribution of water that will take place during methane gas production from a hydrate reservoir. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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14 pages, 4184 KiB

Open AccessArticle

High-Pressure and Automatized System for Study of Natural Gas Hydrates

by Luiz F. Rodrigues, Alessandro Ramos, Gabriel de Araujo, Edson Silveira, Marcelo Ketzer and Rogerio Lourega

Energies 2019, 12(16), 3064; https://doi.org/10.3390/en12163064 - 09 Aug 2019

Cited by 6 | Viewed by 3471

Abstract

Due to the declining of oil reserves in the world in the coming decades, gas hydrate (GH) is seen as the great promise to supply the planet’s energy demand. With this, the importance of studying the behavior of GH, several researchers have been [...] Read more.

Due to the declining of oil reserves in the world in the coming decades, gas hydrate (GH) is seen as the great promise to supply the planet’s energy demand. With this, the importance of studying the behavior of GH, several researchers have been developing different systems that allow greater truthfulness in relation to the conditions where GH is found in nature. This work describes a new system to simulate formation (precipitation) and dissociation of GH primarily at natural conditions at deep-sea, lakes, and permafrost, but also applied for artificial gas hydrates studies (pipelines, and transport of hydrocarbons, CO₂, and hydrogen). This system is fully automated and unique, allowing the simultaneous work in two independent reactors, built in Hastelloy C-22, with a capacity of 1 L and 10 L, facilitating rapid analyses when compared to higher-volume systems. The system can operate using different mixtures of gases (methane, ethane, propane, carbon dioxide, nitrogen, ammonia), high pressure (up to 200 bar) with high operating safety, temperature (−30 to 200 °C), pH controllers, stirring system, water and gas samplers, and hyphenated system with gas chromatograph (GC) to analyze the composition of the gases formed in the GH and was projected to possibility the visualizations of experiments (quartz windows). Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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14 pages, 3025 KiB

Open AccessArticle

Dilation Behavior of Gas-Saturated Methane-Hydrate Bearing Sand

by Shmulik Pinkert

Energies 2019, 12(15), 2937; https://doi.org/10.3390/en12152937 - 31 Jul 2019

Cited by 9 | Viewed by 2554

Abstract

The geotechnical properties of methane-hydrate-bearing sediments (MHBS) are commonly investigated in the laboratory by using artificial hydrate formations in sandy specimens. Analyses of MHBS saturated with gas or water (in addition to methane-hydrate) showed significant mechanical differences between the two pore-filling states. This [...] Read more.

The geotechnical properties of methane-hydrate-bearing sediments (MHBS) are commonly investigated in the laboratory by using artificial hydrate formations in sandy specimens. Analyses of MHBS saturated with gas or water (in addition to methane-hydrate) showed significant mechanical differences between the two pore-filling states. This paper discusses the unique dilatancy behavior of gas-saturated MHBS, with comparison to water-saturated test results of previously-published works. It is shown that the significant compaction of gas-saturated samples is related to internal tensile forces, which are absent in water-saturated samples. The conceptual link between the internal tensile forces and the compaction characteristics is demonstrated through mechanical differences between pure sand and cemented sand. The paper establishes the link between internal adhesion in gas-saturated MHBS and the unique dilation response by using a stress–dilatancy analysis. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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17 pages, 4022 KiB

Open AccessArticle

A 3-In-1 Approach to Evaluate Gas Hydrate Inhibitors

by Narendra Kumar, Niaz Bahar Chowdhury and Juan G. Beltran

Energies 2019, 12(15), 2921; https://doi.org/10.3390/en12152921 - 29 Jul 2019

Cited by 3 | Viewed by 3581

Abstract

With a single apparatus and very short experimentation times, we have assessed phase equilibria, apparent kinetics and morphology of methane gas hydrates in the presence of thermodynamic inhibitors ethane-1,2-diol (MEG) and sodium chloride (NaCl); and kinetic hydrate inhibitor polyvinyl-pyrrolidone (PVP). Tight, local temperature [...] Read more.

With a single apparatus and very short experimentation times, we have assessed phase equilibria, apparent kinetics and morphology of methane gas hydrates in the presence of thermodynamic inhibitors ethane-1,2-diol (MEG) and sodium chloride (NaCl); and kinetic hydrate inhibitor polyvinyl-pyrrolidone (PVP). Tight, local temperature control produced highly repeatable crystal morphologies in constant temperature systems and in systems subject to fixed temperature gradients. Hydrate-Liquid-Vapor (HLV) equilibrium points were obtained with minimal temperature and pressure uncertainties (

u_{T_{avg}} = 0.13

K and

u_{p} = 0.005

MPa). By applying a temperature gradient during hydrate formation, it was possible to study multiple subcoolings with a single experiment. Hydrate growth velocities were determined both under temperature gradients and under constant temperature growth. It was found that both NaCl and MEG act as kinetic inhibitors at the studied concentrations. Finally, insights on the mechanism of action of classical inhibitors are presented. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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20 pages, 4144 KiB

Open AccessEditor’s ChoiceArticle

Hydrate Stability and Methane Recovery from Gas Hydrate through CH₄–CO₂ Replacement in Different Mass Transfer Scenarios

by Jyoti Shanker Pandey and Nicolas von Solms

Energies 2019, 12(12), 2309; https://doi.org/10.3390/en12122309 - 17 Jun 2019

Cited by 44 | Viewed by 4325

Abstract

CH₄–CO₂ replacement is a carbon-negative, safer gas production technique to produce methane gas from natural gas hydrate reservoirs by injecting pure CO₂ or other gas mixtures containing CO₂. Laboratory-scale experiments show that this technique produces low methane [...] Read more.

CH₄–CO₂ replacement is a carbon-negative, safer gas production technique to produce methane gas from natural gas hydrate reservoirs by injecting pure CO₂ or other gas mixtures containing CO₂. Laboratory-scale experiments show that this technique produces low methane volume and has a slow replacement rate due to the mass transfer barrier created due to impermeable CO₂ hydrate layer formation, thus making the process commercially unattractive. This mass-transfer barrier can be reduced through pressure reduction techniques and chemical techniques; however, very few studies have focused on depressurization-assisted and chemical-assisted CH₄–CO₂ replacement to lower mass-transfer barriers and there are many unknowns. In this work, we qualitatively and quantitatively investigated the effect of the pressure reduction and presence of a hydrate promoter on mixed hydrate stability, CH₄ recovery, and risk of water production during CH₄–CO₂ exchange. Exchange experiments were carried out using the 500 ppm sodium dodecyl sulfate (SDS) solution inside a high-pressure stirred reactor. Our results indicated that mixed hydrate stability and methane recovery depends on the degree of pressure reduction, type, and composition of injected gas. Final selection between CO₂ and CO₂ + N₂ gas depends on the tradeoff between mixed hydrate stability pressure and methane recovery. Hydrate morphology studies suggest that production of water during the CH₄–CO₂ exchange is a stochastic phenomenon that is dependent on many parameters. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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23 pages, 9939 KiB

Open AccessEditor’s ChoiceArticle

Thermo-Hydro-Mechanical Coupled Modeling of Methane Hydrate-Bearing Sediments: Formulation and Application

by Maria De La Fuente, Jean Vaunat and Héctor Marín-Moreno

Energies 2019, 12(11), 2178; https://doi.org/10.3390/en12112178 - 07 Jun 2019

Cited by 39 | Viewed by 5218

Abstract

We present a fully coupled thermo-hydro-mechanical formulation for the simulation of sediment deformation, fluid and heat transport and fluid/solid phase transformations occurring in methane hydrate geological systems. We reformulate the governing equations of energy and mass balance of the Code_Bright simulator to incorporate [...] Read more.

We present a fully coupled thermo-hydro-mechanical formulation for the simulation of sediment deformation, fluid and heat transport and fluid/solid phase transformations occurring in methane hydrate geological systems. We reformulate the governing equations of energy and mass balance of the Code_Bright simulator to incorporate hydrate as a new pore phase. The formulation also integrates the constitutive model Hydrate-CASM to capture the effect of hydrate saturation in the mechanical response of the sediment. The thermo-hydraulic capabilities of the formulation are validated against the results from a series of state-of-the-art simulators involved in the first international gas hydrate code comparison study developed by the NETL-USGS. The coupling with the mechanical formulation is investigated by modeling synthetic dissociation tests and validated by reproducing published experimental data from triaxial tests performed in hydrate-bearing sands dissociated via depressurization. Our results show that the formulation captures the dominant mass and heat transfer phenomena occurring during hydrate dissociation and reproduces the stress release and volumetric deformation associated with this process. They also show that the hydrate production method has a strong influence on sediment deformation. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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16 pages, 10132 KiB

Open AccessArticle

Micromechanical Investigation of Stress Relaxation in Gas Hydrate-Bearing Sediments Due to Sand Production

by Eitan Cohen, Assaf Klar and Koji Yamamoto

Energies 2019, 12(11), 2131; https://doi.org/10.3390/en12112131 - 04 Jun 2019

Cited by 19 | Viewed by 3284

Abstract

Past experience of gas production from methane-hydrate-bearing sediments indicates that sand migration is a major factor restricting the production of gas from methane-hydrate reservoirs. One important geotechnical aspect of sand migration is the influence of grain detachment on the existing stresses. This paper [...] Read more.

Past experience of gas production from methane-hydrate-bearing sediments indicates that sand migration is a major factor restricting the production of gas from methane-hydrate reservoirs. One important geotechnical aspect of sand migration is the influence of grain detachment on the existing stresses. This paper focuses on understanding and quantifying the nature of this aspect using different approaches, with a focus on discrete element method (DEM) simulations of sand detachment from hydrate-bearing sand samples. The investigation in the paper reveals that sand migration affects isotropic and deviatoric stresses differently. In addition, the existence of hydrate moderates the magnitude of stress relaxation. Both of these features are currently missing from continuum-based models, and therefore, a new constitutive model for stress relaxation is suggested, incorporating the research findings. Model parameters are suggested based on the DEM simulations. The model is suitable for continuum mechanics-based simulations of gas production from hydrate reservoirs. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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17 pages, 3620 KiB

Open AccessArticle

The Study of Flow Characteristics During the Decomposition Process in Hydrate-Bearing Porous Media Using Magnetic Resonance Imaging

by Kaihua Xue, Lei Yang, Jiafei Zhao, Yanghui Li, Yongchen Song and Shan Yao

Energies 2019, 12(9), 1736; https://doi.org/10.3390/en12091736 - 08 May 2019

Cited by 5 | Viewed by 2523

Abstract

The flow characteristics during decomposition of hydrate-bearing sediments are the most critical parameters for the gas recovery potential from natural gas hydrate reservoirs. The absolute and relative permeability and the flow field distribution during the decomposition process of hydrate-bearing porous media synthetically created [...] Read more.

The flow characteristics during decomposition of hydrate-bearing sediments are the most critical parameters for the gas recovery potential from natural gas hydrate reservoirs. The absolute and relative permeability and the flow field distribution during the decomposition process of hydrate-bearing porous media synthetically created by glass beads are in-situ measured by using magnetic resonance imaging. The absolute permeability value increased slowly, then became stable after the decomposition amount was 50%. The relative permeability change curve is a typical X-shaped cross curve. As the hydrate decomposed, the relative permeability values of the two phases increased, the range of the two-phase co-infiltration zone increased with the increase of relative permeability at the endpoint, and the coexistence water saturation decreased. At the beginning of the decomposition, (hydrate content 100% to 70%), the relative permeability of methane and water rose rapidly from 22% to 51% and from 58% to 70%, respectively. When the amount of the remaining hydrate was less than 50%, the relative permeability curve of the hydrate-bearing glass beads almost kept unchanged. During the hydrate decomposition process, the velocity distribution was very uneven and coincided with the porous media structure. Full article

(This article belongs to the Special Issue Advances in Natural Gas Hydrates)

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