Pore Hydration Research Articles

Selective ion transport through hydrated micropores in polymer membranes.

Ion-conducting polymer membranes are essential in manyseparation processes and electrochemical devices, including electrodialysis1, redox flow batteries2, fuel cells3 and electrolysers4,5. Controlling ion transport and selectivity in these membranes largely hinges on the manipulation of pore size. Although membrane pore structures can be designed in the dry state6, they are redefined upon hydration owing to swelling in electrolyte solutions. Strategies to control pore hydration and a deeper understanding of pore structure evolution are vital for accurate pore size tuning. Here we report polymer membranes containing pendant groups of varying hydrophobicity, strategically positioned near charged groups to regulate theirhydration capacity and pore swelling. Modulation of thehydrated micropore size (less thantwo nanometres) enables direct control over water and ion transport across broad length scales, as quantified by spectroscopic and computational methods. Ion selectivity improves in hydration-restrained pores created by more hydrophobic pendant groups. These highly interconnected ion transport channels, with tuned pore gate sizes, show higher ionic conductivity and orders-of-magnitude lower permeation rates of redox-active species compared with conventional membranes, enabling stable cycling of energy-dense aqueous organic redox flow batteries. This pore size tailoringapproach provides a promising avenue to membranes with precisely controlled ionic and molecular transportfunctions.

Small Molecule NS11021 Promotes BK Channel Activation by Increasing Inner Pore Hydration.

The Ca2+ and voltage-gated big potassium (BK) channels are implicated in various diseases, including heart disease, asthma, epilepsy, and cancer, but remain an elusive drug target. A class of negatively charged activators (NCAs) have been demonstrated to promote the activation of several potassium channels including BK channels by binding to the hydrophobic inner pore, yet the underlying molecular mechanism of action remains poorly understood. In this work, we analyze the binding mode and potential activation mechanism of a specific NCA named NS11021 using atomistic simulations. The results show that NS11021 binding to the pore in deactivated BK channels is nonspecific and dynamic. The binding free energy of -8.3 ± 0.7 kcal/mol (KD = 0.3-3.1 μM) calculated using umbrella sampling agrees quantitatively with the experimental EC50 range of 0.4-2.1 μM. The bound NS11021 remains dynamic and is distal from the filter to significantly impact its conformation. Instead, NS11021 binding significantly enhances the pore hydration due to the charged tetrazol-phenyl group, thereby promoting the opening of the hydrophobic gate. We further show that the free energy barrier to K+ permeation is reduced by ∼3 kcal/mol regardless of the binding pose, which could explain the ∼62-fold increase in the intrinsic opening of BK channels measured experimentally. Taken together, these results support the idea that the molecular mechanism of NS11021 derives from increasing the hydration level of the conformationally closed pore, which does not depend on specific binding and likely explains the ability of NCAs to activate multiple K+ channels.

Gas flow in frozen hydrate-bearing sediments exposed to compression and high-pressure gradients: Experimental modeling

Changes in temperature and pressure patterns in gas- and hydrate-saturated permafrost caused by natural geodynamic processes or human impacts can lead to the active flow of gas through unfrozen zones, and its explosive emission is often accompanied by crater formation. Gas flow and accumulation in the shallow permafrost can be explained by the conditions of gas pressure equal to or exceeding the overburden pressure and high-pressure gradients. For the first time, filtration tests were conducted on ice- and hydrate-saturated rocks under uniaxial compression at various negative temperatures using a developed methodology. The modeling of gas flow in a mixture of ice-saturated sand and 25 % montmorillonite at gas pressure gradients within 2 MPa, shows that gas flow can start at warm negative temperatures near the thaw point. Pore hydrate formation in frozen sand heated to positive temperatures and frozen back led to a linear decrease in gas permeability by up to eight times. However, the behavior of gas permeability during hydrate dissociation is nonlinear as it increased within a few hours after the onset of dissociation, but then decreased exponentially in the following 24 h.

P-wave velocity evolution and interpretation of seepage mechanisms during CO2 hydrate formation in quartz sands: Perspective of hydrate pore habits

The hydrate-based CO2 storage (HBCS) is a promising technology for controlling CO2 emissions. A comprehensive understanding of the hydrate pore habits and seepage mechanism of hydrate-bearing sediments (HBSs) could provide a theoretical basis for HBCS. In the study, the hydrate occurrence characteristics, water migration and P-wave velocity response during hydrate formation in quartz sands are investigated. In addition, a new theoretical equation that relates P-wave velocity to permeability is presented. The digital core of porous media containing hydrate is also established, and the seepage characteristics during hydrate formation are revealed by numerical simulation. The results show that hydrates are preferentially generated in large pores and initially appear in a non-cementing pore-filling pattern, while an annular flow path for water is formed in quartz sands during hydrate formation. The hydrate morphology is changed from a pore-filling pattern to a patchy pattern at a critical hydrate saturation of around 3–7% for quartz sands with various particle diameters. The formation sites and spatial heterogeneity of hydrates can be depicted by the evolution pattern of streamlines. The results of the experiments indicate that the new semiempirical model is effective for estimating the permeability from the P-wave velocity of HBSs. These findings offer significant theoretical and practical insights for HBCS in porous media.

Effect of gravel pack permeability on horizontal well productivity loss under secondary methane hydrate formation: Experimental optimization of 3D randomly distributed mixed sand pack

Horizontal well productivity is limited by secondary hydrate formation (temperature drop results from endothermic of hydrate dissociation) during production. Seepage capacity as one of the key indexes for evaluating production efficiency, and efficiency is declined by sand production. Sand control is achieved by using gravel pack technology (selected sands for hindering the sediments particles migration), which extends the production time. However, forecasting the productivity decline trend from quantifying the permeability of the gravel pack after secondary formation remain challenges. To address these issues, a randomly distributed 3D normalized permeability (Kr) model was developed to describe the seepage capacity of gravel pack composed by various particle sizes of mixed glass beads. The theoretical modelling was established by observing micro spatial structure of glass beads with hydrate formation. The new model considered three consolidation modes of hydrate in pores (cementing + bearing, pore filling, and grain coating) and linked them with the productivity ratio equation of a horizontal gas well. To confirm the viability of the model, a series of permeability measurement experiments with various size ratios (α) from 1 to 10 were conducted. Finally, errors comparison and all parameters of the model were analyzed. The results showed that the productivity ratio declined clearly after saturation is >0.79, when α = 4. For long-term production, α = 10 would be better. The new model can help hydrate horizontal wells increase production from laboratory to industrial exploitation. KeyPoints•Secondary hydrate formation permeability model in gravel pack was established.•After secondary saturation's effect on horizontal well production was developed.•Gravel pack was simulated by random non-coincident particles with varies size ratios.•When the size ratio is 4, productivity ratio of horizontal well was extended.

Intrinsic correlation between the generalized phase equilibrium condition and mechanical behaviors in hydrate-bearing sediments

The phase equilibrium and mechanical behaviors of natural gas hydrate-bearing sediment are essential for gas recovery from hydrate reservoirs. In heating closed systems, the temperature-pressure path of hydrate-bearing sediment deviates from that of pure bulk hydrate, reflecting the porous media effect in phase equilibrium. A generalized phase equilibrium equation was established for hydrate-bearing sediments, which indicates that both capillary and osmotic pressures cause the phase equilibrium curve to shift leftward on the temperature-pressure plane. In contrast to bulk hydrate, hydrate-bearing sediment always contains a certain amount of unhydrated water, which keeps phase equilibrium with the hydrate within the hydrate stability field. With changes in temperature and pressure, a portion of pore hydrate and unhydrated water may transform into each other, affecting the shear strength of hydrate-bearing sediment. A shear strength model is proposed to consider not only hydrate saturation but also the change in temperature and pressure of hydrate-bearing sediment. The model is validated by experimental data with various hydrate saturation, temperature and pressure conditions. The deformation induced by partial dissociation was studied through depressurization tests under constant effective stress. The reduction in gas pressure within the hydrate stability field indeed caused sediment deformation. The dissociation-induced deformation can be reasonably estimated as the difference in volume between hydrate-bearing and hydrate-free sediments from the compression curves.

Three-dimensional pore-scale study of methane hydrate dissociation mechanisms based on micro-CT images

<p>Methane hydrate is a promising source of alternative energy. An in-depth understanding of the hydrate dissociation mechanism is crucial for the efficient extraction. In the present work, a comprehensive set of pore-scale numerical studies of hydrate dissociation mechanisms is presented. Pore-scale lattice Boltzmann (LB) models are proposed to simulate the multiphysics process during methane hydrate dissociation. The numerical simulations employ the actual hydrate sediment pore structure obtained by the micro-CT imaging. Experimental results of xenon hydrate dissociation are compared with the numerical simulations, indicating that the observed hydrate pore habits evolution is accurately captured by the proposed LB models. Furthermore, simulations of methane hydrate dissociation under different sediment water saturations, fluid flow rates and thermal conditions are conducted. Heat and mass transfer limitations both have significant effects on the methane hydrate dissociation rate. The bubble movement can further influence the dissociation process. Dissociation patterns can be divided into three categories, uniform, non-uniform and wormholing. The fluid flow impacts hydrate dissociation rates differently in three-dimensional real structures compared to two-dimensional idealized ones, influenced by variations in hydrate pore habits and flow properties. Finally, upscaling investigations are conducted to provide the permeability and kinetic models for the representative elementary volume (REV)-scale production forecast. Due to the difference in the hydrate pore habits and dissociation mechanisms, the three-dimensional upscaling results contrast with prior findings from two-dimensional studies. The present work provides a paradigm for pore-scale numerical simulation studies on the hydrate dissociation, which can offer theoretical guidance on efficient hydrate extraction.</p>

Mechanical behaviour and microstructure of methane hydrate-bearing sandy sediment observed at various spatial scales

Methane hydrates (MHs) are considered an alternative energy resource but also a potential source of geo-hazards and climate change. The physical/mechanical properties of gas hydrate-bearing sandy sediments are strongly dependent on the distribution of hydrates within the pore space. The purpose of this study is to investigate morphologies and pore-habits of MHs formed in sandy sediments by means of experiments that probe a wide range of scales, from the pore scale – using Synchrotron X-Ray Computed Tomography (SXRCT) and optical microscopy – to the core scale, through mechanical property measurements. The same synthetic sands are used, in which MHs are generated successively under excess gas and excess water conditions. At the macroscopic (core) scale, MH pore habits are inferred by comparing the measured sonic wave velocities to velocities calculated from rock physics models and further assessed via triaxial compression tests. Furthermore, Magnetic Resonance Imaging is used to investigate the kinetics of MH formation and distribution along the core height. The pore habits and MH morphologies are directly visualized at the pore (grain) scale by SXRCT and, with still better spatial and temporal resolution, by transmission optical microscopy, revealing some more complex morphologies than in the hydrate pore habits commonly admitted.

Shear strength degradation of gas hydrate-bearing sediment due to partial hydrate dissociation

Extraction of methane hydrate from subseafloor reservoir may potentially trigger seabed slides and induce subsidence. To address the problems, it is crucial to properly characterize the phase equilibrium condition of pore hydrate and the shear strength of the soil. As one of the key constitutive components, the phase equilibrium condition enforces a constraint over pore gas pressure, temperature and unhydrated water content. Such a constraint, however, has been traditionally ignored in analyzing the mechanical behavior of hydrate-bearing soil. In this paper, a series of stepwise hydrate dissociation tests was performed, and the phase equilibrium condition of pore hydrate was determined, providing an effective way to evaluate the unhydrated water content during hydrate dissociation. Meanwhile, a series of direct shear tests was also conducted to explore the shear strength characteristics of the soil. It is shown that the shear strength of the hydrate-bearing soil can be significantly influenced by pore gas pressure, unhydrated water content, hydrate saturation and several other factors. In particular, the measured shear strength depends upon the initial water content of the sample, pointing to a potential problem that the shear strength could be wrongly determined if not properly interpreted. A shear strength criterion, which enforces the equilibrium condition of pore hydrate, is developed for hydrate-bearing soil, establishing a link between the equilibrium condition and the shear strength. The proposed equation describes well the shear strength characteristics of hydrate-bearing soils, remarkably unifying the effects of pore pressure, temperature, water content and hydrate saturation.

Theoretical analysis of shape factor of gas hydrate sediments under stress dependence

The Kozeny-Carman (KC) equation is used extensively to characterize the effective permeability of gas hydrate sediments. However, most existing modeling approaches ignore the changes in the effective stress, hydrate saturation, and pore structures of porous media, which significantly affect the extraction and exploration of gas hydrates. In addition, theoretical models that can accurately describe shape factors during the imbibition process and predict the effective permeability of gas hydrate sediments are rarely reported. This paper proposes a theoretical stress-dependent shape factor model to study the physical relations between the shape factor and relevant parameters (e.g., effective stress, hydrate saturation, effective porosity, and pore fractal dimension). Then, the derived model is extended to study the shape factor during the imbibition process. The two main novel features of the proposed model are: (1) it takes the effective stress, hydrate saturation, and pore structures into account; and (2) it can be used to study the evolution of shape factors during the imbibition process in gas hydrate sediments. The predictions from the developed model provide a good agreement with experimental results, which validates the model. In addition, based on the derived model, the effects of relevant parameters on shape factors are studied theoretically. From a practical standpoint, the model can not only estimate the effective permeability of gas hydrate sediments under stress dependence but also provide insight into the evolution of shape factor, pore structures (e.g., capillary total number, pore fractal dimension, tortuosity fractal dimension, and effective porosity) and hydrate pore habits during the extraction of hydrates.

Multiple-Point Geostatistics Simulation of the Natural Gas Hydrate Distribution at the Pore Scale

Heat and mass transfer in a natural gas hydrate reservoir is strongly affected by the hydrate pore habit. Some present simplified models used in numerical simulation of a hydrate-bearing sediment are difficult to catch features of the hydrate distribution in sediments precisely. Using an improved multiple-point geostatistics simulation method, this study generates a series of images of porous media that reproduce the hydrate distribution information on a training image. The improved algorithm completely solves the problem that the hydrate blocks the boundary and makes the variogram and visual properties similar to the training image. Some typical phenomena of hydrate formation appear in the results, such as Ostwald ripening and the shift of hydrate pore habit from grain coating toward pore filling. The feasibility of predicting the pore habit of a hydrate with time using this novel method is proven by the verification case. This study offers a new approach to predict the distribution behavior of a hydrate, and this algorithm may be applied widely by scanning training images from different reservoirs.

A novel permeability model for hydrate-bearing sediments integrating pore morphology evolution based on modified Kozeny-Carman equation

Permeability of hydrate-bearing sediments is the key parameter to determine the gas production performance, which is mainly affected by the pore morphology and hydrate saturation. Existing models of permeability could not well capture the dynamic characteristic of permeability in sediments with changing hydrate saturation and pore morphology. In this paper, a novel normalized permeability model using logistic function linked different hydrate pore morphology evolution was established by modifying tortuosity, surface area and pore shape factor simultaneously in Kozeny-Carman equation. It was verified by different published data and compared with other models. The introduced critical hydrate saturation and transitional intensity of hydrate pore morphology were optimized by genetic algorithm. Results indicated that this model was more powerful than existed models and better captured the permeability evolution in hydrate-bearing sediments at various conditions. The critical hydrate saturation and transitional intensity of hydrate pore morphology dominated the characteristics of permeability evolution. In addition, the effect of porosity would not be ignored especially below the critical hydrate saturation when hydrate pore morphology changed from pore filling to grain coating. The proposed model brings reliable predictions and mechanistic understandings of the permeability evolution in hydrate-bearing sediments, and builds fundamental theory for development of natural gas hydrate in safety and efficiency.

Discrete Element Modeling of the Effect of Hydrate Distribution Heterogeneity on the Mechanical Behavior of Cemented Hydrate-Bearing Sediments

Hydrate distribution heterogeneity is often observed in natural and artificial hydrate-bearing sediments (HBSs). To capture hydrate distribution heterogeneity, a pore-scale method is proposed to model cemented HBSs using the discrete element method (DEM). This method takes into account the quantitative effect of hydrate saturation in a sediment pore on the contact bond parameters surrounding the pore. A series of DEM specimens with different macroscopically and microscopically heterogeneous hydrate distributions are prepared. The mechanical behavior of heterogeneous HBSs is investigated by performing biaxial compression tests with flexible boundaries. The simulation results show that both macroscopic and microscopic hydrate distribution heterogeneity can influence the mechanical properties of HBSs. The shear strength is promoted in both macroscopically and microscopically heterogeneous HBSs. Longitudinally heterogeneous HBSs have a higher secant modulus, while transversely heterogeneous HBSs have a lower secant modulus than homogeneous HBSs. The secant modulus of microscopically heterogeneous HBSs first increases and then decreases with increasing pore hydrate saturation. It is found that the deformation behavior and bond breakage evolution of HBSs depend on hydrate distribution heterogeneity. These findings can provide insights into understanding the mechanical behavior of natural HBSs with heterogeneous hydrate distributions.

Upscaling methane hydrate dissociation kinetic model during depressurisation

In the present work, a pore-scale numerical simulation of methane hydrate dissociation by depressurisation is conducted to analyze the effect of heat and mass transfer on the dissociation rate for scaling up the kinetic model at the representative element volume (REV) scale. The mass transport limitation shows that the hydrate dissociation preferred to occur near the gas phase. The effective reaction surface area is introduced to measure the exposed hydrate surface to the gas phase during gas and water migration and is modelled as a function of local hydrate and water saturation and hydrate pore habits. Heat transport limitation is computed with the one-temperature model due to the local thermal equilibrium. Compared to the pore-scale simulation, the proposed REV-scale kinetic model predicts dissociation rates with a relative error of less than 10%, which is expected to increase the precision of the hydrate recovery forecast.

Inner pore hydration free energy controls the activation of big potassium channels

Hydrophobic gating is an emerging mechanism in regulation of protein ion channels where the pore remains physically open but becomes dewetted to block ion permeation. Atomistic molecular dynamics simulations have played a crucial role in understanding hydrophobic gating by providing the molecular details to complement mutagenesis and structural studies. However, existing studies rely on direct simulations and do not quantitatively describe how the sequence and structural changes may control the delicate liquid-vapor equilibrium of confined water in the pore of the channel protein. To address this limitation, we explore two enhanced sampling methods, namely metadynamics and umbrella sampling, to derive free-energy profiles of pore hydration in both the closed and open states of big potassium (BK) channels, which are important in cardiovascular and neural systems. It was found that metadynamics required substantially longer sampling times and struggled to generate stably converged free-energy profiles due to the slow dynamics of cooperative pore water diffusion even in the barrierless limit. Using umbrella sampling, well-converged free-energy profiles can be readily generated for the wild-type BK channels as well as three mutants with pore-lining mutations experimentally known to dramatically perturb the channel gating voltage. The results show that the free energy of pore hydration faithfully reports the gating voltage of the channel, providing further support for hydrophobic gating in BK channels. Free-energy analysis of pore hydration should provide a powerful approach for quantitative studies of how protein sequence, structure, solution conditions, and/or drug binding may modulate hydrophobic gating in ion channels.

Methane Gas Bubbles Affecting the Formation and Distribution of Hydrates in Kaolinite Slit Pores: A Molecular Dynamics Study

Molecular dynamics simulations are applied to study the formation and distribution of hydrates in kaolinite slit pores with methane gas bubbles adsorbed on one of the pore surfaces. The results show that hydrates nucleate in the bulk of solution in pores and then grow into hydrate shells around methane gas bubbles. These hydrate shells can hinder the diffusion of methane molecules. As the result, the formed hydrates cement and distribute near the kaolinite surfaces, on which methane gas bubbles have been adsorbed before hydrate formation. Because of the adsorption of dissolved methane molecules on siloxane surfaces, methane gas bubbles are highly dynamic, with more methane molecules exchanging between bubbles and solution. Therefore, the dissolution of methane molecules is promoted, which is beneficial for hydrate formation. However, in siloxane–siloxane pores, the strong adsorption effect of siloxane surface leads to the generation of layer-like bubbles, inhibiting hydrate formation by providing a relatively low methane concentration in solution. Methane gas bubbles can be directly adsorbed on siloxane surfaces, while water molecules exist between methane gas bubbles and gibbsite surfaces. Six-water rings can be induced by methane gas bubbles on gibbsite surfaces, which may promote hydrate formation by providing partial structures of hydrate cages. The formation behaviors and distribution characteristics of hydrates in kaolinite pores with methane gas bubbles are different from those in kaolinite pores with homogeneous methane solution. The results obtained can help to understand the different formation behaviors and distribution characteristics of hydrates in sediments.

Hydrophobic gating in bundle-crossing ion channels: A case study of TRPV4.

Many transmembrane (TM) ion channels regulate ion permeation by forming bundle crossing of the pore-lining TM helices when deactivated. The resulting physical constriction is generally believed to serve as the “gate” and impose the major free energy barrier to ion permeation. On the other hand, many ion channels have been observed contain inner pores that are highly hydrophobic and can undergo spontaneous dewetting transitions. The resulting “vapor” region can block ion flow even in the absence of physical constriction. However, it is not clear whether such hydrophobic gating mechanism could be involved in channels with bundle-crossing in the deactivated state. Using atomistic simulations, we show that the human TRPV4 (hTRPV4) channel in the bundle-crossing closed state can readily undergoes hydrophobic dewetting transition and forms a vapor region in the lower pore region. Importantly, free energy analysis reveals that the major barrier for ion permeation is not located at the most constricted site, but within the vapor region. Furthermore, a single hydrophilic mutation I715N in the lower pore region significantly increases pore hydration without affecting the physical opening near bundle crossing; yet it largely removes the free energy barrier of ion permeation in hTRPV4, consistent with a previous experimental study showing that I715N leads to a constitutively conductive channel. Therefore, hTRPV4 is a hydrophobic gating channel despite the presence of bundle-crossing in the deactivated state. We anticipate that hydrophobic gating may play a key role in other bundle-crossing ion channels with hydrophobic inner pores.

Phase Equilibrium of Methane Hydrate in Sediments: Experimental and Theoretical Characterization

A series of phase equilibrium tests were performed to explore the influence of various experimental conditions, including initial water content, dry density, and salt content, on the phase equilibrium behavior of methane hydrate in fine- and coarse-grained sediments. The results indicate that the phase equilibrium condition of pore hydrate is significantly influenced by the adopted experimental conditions and the sediment types. It is shown that in equilibrium, a unique relationship (the soil hydration characteristic curve (SHCC)) exists among the temperature shift, the unhydrated water, and the amount of dissolved salt. Under salt-free conditions, the SHCC is independent of dry density for coarse-grained specimens, whereas it is slightly influenced by the dry density for fine-grained specimens. A recently developed phase equilibrium model of pore hydrate, which can account for osmotic, capillary, and adsorptive effects, is introduced to interpret the experimental results. It is shown that the SHCC of the coarse-grained specimens can be very well described by the model; for fine-grained specimens, however, the effect of salt content on matric suction has to be taken into account in the model prediction.

Influencing Factors of Hydration Number of Synthesized Methane Hydrates in Sediment

The low-field NMR method is introduced to explore the effect of various experimental conditions on hydration number during hydrate dissociation in methane hydrate-bearing sediments. It is shown that the NMR signal peak value of water is independent of the dry density of sediment, gas pressure, and salt concentration and significantly influenced by temperature. A relationship among NMR signal peak value, substance content, pressure, and temperature is developed to estimate the hydration number of pore hydrates during hydrate dissociation. It is revealed that the hydration number (Nh) of synthesized methane hydrates remains practically unchanged during hydrate dissociation in fine-grained sediments and is trivially influenced by experimental conditions, including initial pressure, density, initial water saturation, and salt content. Our experimental results indicated that the hydration number of methane hydrates is about 6.5, which is slightly higher than that of natural hydrates.

Pore-scale modeling of seepage behaviors and permeability evolution in heterogeneous hydrate-bearing sediments and its implications for the permeability model

Permeability is one of the key factors determining the recovery of gas resources from natural gas hydrate (NGH) reservoirs. The heterogeneous distribution of hydrates induced by random nucleation and growth in the pore space of hydrate-bearing sediments (HBS) inevitably results in pore space structure change, thereby significantly affecting fluid flow and permeability. In this paper, the seepage behaviors in a series of two-dimensional (2D) idealized HBS models were simulated based on the pore-scale computational fluid dynamics (CFD) modeling to obtain permeability and pore-scale seepage field. The 2D hydrate heterogeneity degree coefficient (DH) was proposed to quantitatively characterize the hydrate distribution heterogeneity. The pore-throat evolution characteristics were quantified by average pore-throat size and pore-throat size distribution. The results show that the occurrence and growth of hydrates within pores lead to the reconstruction and evolution of pore space structure and the formation of new fluid migration channels. The main reason for the reduction of HBS permeability is that with the increase of hydrate saturation, pores and throats with small sizes gradually become dominant, pore space connectivity is weakened, and the tortuosity for fluid flow increases. Additionally, the evolution of flow path and flow channel morphology caused by the growth of hydrates with different pore habits leads to the difference in pore-scale seepage behaviors and permeability variations in the homogeneous model. However, the effect of hydrate pore habits on permeability is no longer obvious due to the spatial heterogeneity of sediment grains and gas hydrates in the heterogeneous model. The effective flow path for pore fluid controlled by overall hydrate distribution and pore-throat characteristics would be critical. The comparison of calculated permeability results reveals that the accuracy of reported permeability reduction models is limited due to the ignorance of the HBS heterogeneity, the actual hydrate pore habits and morphology, and the pore structure geometry. It is hoped that the findings of this study can provide some insights into the pore-scale seepage characteristics of HBS, providing important implications for the development of the permeability model that can be easily implemented in the numerical simulators for field-scale gas production optimization of hydrate reservoir.