Hydrate Dissociation Process Research Articles

Kinetic study on the effect of ice nucleation and generation on methane hydrate dissociation below the quadruple point

Natural gas hydrates (NGHs) have captured worldwide attention because of its huge resources and high energy density. Deep depressurization by dropping the pressure below the quadruple point is recognized as a promising exploitation method. However, the impact of ice formation on NGHs dissociation within depressurization is still controversial. Thus, we examine the dissociative behavior of NGHs at low temperature below the quadruple point using a high-pressure reactor. It primarily focuses on how ice formation affects heat and mass transfer, as well as the kinetics of hydrate dissociation. The results indicate that during the hydrate dissociation process, liquid water initially transforms into metastable supercooled water, which then transitions to solid ice under external disturbance. Ice nucleation predominantly occurs in two locations: within the free water phase and on the surface of hydrate particles. A double-edged effect of ice on NGHs dissociation is observed: the latent heat released by ice nucleation and generation could accelerate the hydrate breakdown (positive effect), while the decrease in permeability along with the self-preservation effect from ice formation tends to inhibit the NGHs dissolution (negative effect). In addition, a higher pressure drawdown rate can accelerate both ice nucleation and formation, which in turn shortens the freezing induction time. The increase of water saturation (SA) and the decrease of hydrate saturation (SH) can significantly reduce the mining time and strengthen both the hydrate dissociation rate (QH) and gas production rate (QP). Therefore, hydrate sediments with higher SA or lower SH are more conductive to gas recovery of low-temperature NGHs deposits in permafrost regions.

An x-ray computed tomography gas hydrate in situ formation and seepage simulation device.

Nano-CT (computed tomography) technology enables high-resolution imaging and scanning of hydrate dissociation processes in porous media at submicron-scale resolution. However, due to the inability of nano-CT to withstand large torque, the traditional semiconductor cooling method cannot be used for in situ hydrate formation, resulting in the hindering of the effective operation of seepage simulators. Therefore, in this paper, a nano-CT-based in situ hydrate formation and seepage simulator are specially designed, and the torque and entanglement problems existing in traditional experimental devices can be solved by using a pipeline placed above the device and a built-in seepage line. The device is able to offer an improved depiction of hydrates in porous media and the effect of the seepage process on the three-dimensional distribution of hydrates. The future applications of this device are expected to provide novel insights into the effects of gas-water transport and hydrate storage patterns during gas hydrate exploitation.

A granular thermodynamic constitutive model considering THMC coupling effect for hydrate-bearing sediment

The interaction among mechanical, hydraulic, and temperature fields plays a crucial role in determining gas production efficiency and reservoir mechanical response. Considering particle rearrangement and cementation degradation effect, this study establishes a thermodynamic model that couples thermal, hydraulic, mechanical, and chemical fields (THMC) for hydrate-bearing sediments. For the proposed model, the mechanical field incorporates pore pressure and cementation terms, the hydraulic field considers the porosity, volumetric strain, and thermal driving effect, and the thermal field couples heat conduction, heat convection, and energy dissipation from hydrate dissociation. Furthermore, gas/liquid seepage rate and temperature conservation equation are not introduced as assumptions but are inferred from thermodynamic identities. Numerical simulations are conducted to investigate the physical significance of the three coupling elements and the mechanism of crucial parameters influencing gas production efficiency and reservoir mechanical response. The proposed model is simulated and validated at varying hydrate saturation levels and depressurization pressures. The modeling outcomes indicate that the theoretical model can accurately anticipate mechanical responses, gas production efficiency, and temperature variations during the hydrate consolidation and dissociation process.

Application of coupled hydrodynamic and thermal Lattice–Boltzmann simulation on permeability estimation of hydrate-bearing sediment during hydrate dissociation processes

Natural gas hydrates, which are plentifully distributed in ocean floor sediments and permafrost regions, are considered a promising unconventional energy resource. The current hydrate production approaches aim at breaking the thermodynamic equilibrium state to stimulate hydrate dissociation that releases methane and water molecules, which causes formation porosity and permeability alteration. Efficient estimation of permeability during hydrate dissociation is essential to evaluate the economic feasibility for gas production from hydrate-bearing sediment. In this paper, we developed a coupled hydrodynamic and thermal Lattice–Boltzmann (LB) method to rigorously model the coupled processes of mass transfer, conjugate heat transfer, and fluid flow during the hydrate dissociation. We then carried out numerical simulation on the dissociation processes of hydrate formation with the three most common hydrate distribution morphologies, pore-filling, grain-coating and dispersed, under two production approaches that are depressurization, and depressurization with thermal intervention. Our simulation results indicated that the coupling of gas transport and heat transfer has significant impact on pore geometry evolution, especially pore connectivity, during hydrate dissociation processes due to the endothermic nature of the dissociation processes. Therefore, it is vital to consider the coupling effects for estimation of hydrate formation permeability through numerical simulations.

SEM/Raman spectroscopy of clathrites as analogs of authigenic carbonates in ocean worlds

AbstractThere is evidence from the near‐infrared observations of space missions of the presence of carbonates on the surface of several ocean worlds. However, their genesis remains unresolved. We investigate the hypothesis that these carbonates may be in the form of clathrites assuming that clathrate hydrates are stable phases in the crust and ocean of these ocean worlds. In order to support this, we studied a sample of a potential clathrite from the Hydrate Ridge cold seep (Cascadia Subduction Zone), the carbonate rock fossil of clathrate hydrates, as a terrestrial analogue. We characterised the mineralogy and texture of the sample by using a coupled confocal Raman microscope and scanning electron microscopy instrument with the aim of identifying possible geo‐ and biosignatures, which could be relevant for future missions of exploration to ocean worlds and Mars. Our results show that aragonite is the dominant mineral phase in the clathrite sample, but Mg‐calcite and dolomite were also identified. These three carbonates constitute a pattern related to clathrate hydrate formation and dissociation processes. Dolomite was defined as a biosignature of gas hydrate microbiomes because it was integrated within Mg‐calcite grains precipitated after clathrate hydrate dissociation. Nevertheless, no spectral changes were observed in Raman bands of carbonate minerals that would indicate the influence of clathrate hydrates in their genesis. We also observed that Raman band positions of the associated framboidal pyrites are a characteristic signature of the associated framboid‐like texture because its potential as biosignature may only be attributed by biochemical analysis.

Permeability anisotropy analysis of two-phase flow during hydrate dissociation process

Natural gas hydrate (NGH) is a versatile and energy source. But in the actual extraction process, NGH in the reservoir will be out of phase equilibrium conditions and dissociate. This will induce alterations in permeability characteristics of reservoir and will exert a significant influence on the assessment of hydrate reservoir capacity. In the research, an innovative CT triaxial system was used to obtain the micro-structure of sediment specimen during hydrate dissociation. The anisotropy of absolute permeability (k), capillary pressure (Pc) and relative permeability (kr) were also analyzed using the pore network model (PNM). As demonstrated by the results, k increases gradually in all three directions during the dissociation. Pc gradually decreases. The degree of anisotropy of both Pc and gas-water relative permeability (krg and krw) gradually decreases. The impact of hydrate dissociation on the kr anisotropy during primary gas flooding surpasses that observed during secondary water flooding. As hydrate saturation decreases, the krw increases and the krg decreases in the horizontal directions. The krw does not change significantly and the krg increases in the vertical direction. Along the length of the sample, the distribution of hydrate and pore space exhibits heterogeneity across the sections. This inhomogeneous distribution will lead to anisotropy in permeability.

Assessment of Production Performance and Uncertainty in the UBGH2-6 Gas Hydrate Reservoir, Ulleung Basin

This study delineates the intricate dynamics of gas hydrate production in the UBGH2-6 reservoir, located in the Ulleung Basin, by deploying a comprehensive simulation model. By integrating a sensitivity analysis with Latin hypercube sampling-based Monte Carlo simulations, we evaluated the influences on gas and water production and explored the underlying uncertainties within this gas hydrate reservoir. The simulation model revealed significant findings, including the production of approximately 440 t of gas and 34,240 t of water, facilitated by a depressurization strategy at 9 MPa for a year. This highlights the pivotal roles of porosity, permeability, and thermal properties in enhancing production rates and influencing hydrate dissociation processes. Sensitivity analysis of 19 parameters provides insights into their impact on production, identifying the key drivers of increased production rates. Furthermore, uncertainty analysis examined 300 reservoir models, utilizing statistical percentiles to quantify uncertainties, projecting a median gas production of approximately 455 t. This study identifies critical factors affecting gas hydrate production and offers valuable insights for future exploration and exploitation strategies, making a significant contribution to the field of gas hydrate research.

Eco-friendly hydrogels serving as water carriers for improving methane hydrate formation and dissociation processes

Natural gas hydrate (NGH) technology has broad application prospects in natural gas storage & transportation. In this work, we used eco-friendly hydrogel-based carriers to retain water, which were biodegradable polyvinyl alcohol-co-acrylic acid (PVA-co-PAA) hydrogels, and to react with methane gas and form hydrates. Results indicated that hydrates could be formed in the presences of swollen hydrogel particles without stirring or promoter adding, which might be owed to the enlarged gas–liquid interface and bulk of hydrophilic groups. When mass ratio of PVA to AA (MR) was 1:4, hydrogels performed best in improving hydrate formation kinetics: the induction time was 20.3 ± 20 min, the hydrate growth rate was 0.0217 ± 0.0088 mmol mL−1 min−1, and the methane uptake was 75.84 ± 4.70 mmol mol−1 water. Morphological observations revealed the water retaining behaviors of hydrogels during hydrate formation-dissociation process: a part of absorbed water transferred out of hydrogels to participate in hydrate formation, and afterwards hydrogels could re-absorbed the water released by hydrate dissociation. Moreover, hydrogels kept excellent recycling performance in seven repeated hydrate formation-dissociation cycles. Collectively, PVA-co-PAA hydrogels used as water carriers could improve mass transfer and reaction efficiency during methane hydrate formation-dissociation process, and meanwhile exhibited good recyclability due to strong water absorbing and retaining capabilities, implying that PVA-co-PAA hydrogels might potentially have broad applications in NGH technology.

Heat and mass transfer analysis during the process of methane hydrate dissociation by thermal stimulation

Natural Gas Hydrate (NGH) is characterized by large reserves and cleanliness, which has attracted wide attention around the world. Thermal stimulation is considered to be one of the possible methods to facilitate hydrate dissociation. In this paper, the hydrate is dissociated through injecting hot water. In order to reveal the influence of the speed and the temperature of injected hot water on the temperature distribution, hydrate dissociation front, gas production rate, and cumulative gas production, a 2D cylindrical mathematical model of thermally-induced hydrate dissociation was established. The results show that the dissociation process can be regarded as a moving boundary ablation process. The dissociation front divides the whole reservoir into three sections: complete dissociation section, ongoing dissociation section, and undissociated section, and the range of ongoing dissociation section is a very narrow area characterized by a relatively intensive temperature contour, which indicates that the temperature drops rapidly during the hydrate dissociation. The temperature at the dissociation front is almost constant under different hot water injection speeds or temperatures. The injection speed and the temperature of hot water seem to have similar effects on hydrate dissociation. The enhanced hot water injection speed or hot water injection temperature will result in a faster gas production rate, a quicker movement of the dissociation front, and a shorter duration time of gas production, however, hot water injection speed and temperature have little impact on the final gas production. The results may provide a guidance for safely and efficiently exploiting NGH.

FORMATION AND DISSOCIATION OF CO2 HYDRATES WITHIN A NATURAL BASALTIC-BASED POROUS MEDIUM FROM ICELANDIC MARGINS

Carbon dioxide hydrates were formed and dissociated in a lab-scale apparatus, filled with demineralized water and porous sediments. Two different porous media were tested; the first consists of glass beads, commonly used to reproduce marine environments during lab-scale hydrate formation experiments. Natural basaltic sand, typical of the Icelandic margins, was chosen as second sediment. The role played by the two sediments was analyzed during both the hydrate formation and dissociation processes and the results were compared with each other. In particular, the pressure-temperature values measured during the dissociation phase were compared with the phase boundary equilibrium conditions for pure carbon dioxide hydrates, carried out in the absence of any porous sediment, collected from the scientific literature. The presence of porous sand favored the preservation of hydrates during the dissociation phase; in detail, hydrates melted at pressures 1.1 bar higher (on average) in the presence of glass beads, and 1.0 bar higher with the basaltic sand. The formation was more abundant in the presence of glass beads: 0.227-0.232 mol of hydrates were produced, against 0.141-0.21 mol achieved when the basaltic sediment was used.

Evaluating CO2 hydrate kinetics in multi-layered sediments using experimental and machine learning approach: Applicable to CO2 sequestration

The transition to a low-carbon economy requires the implementation of effective carbon capture and sequestration (CCS) strategies. One of the potential CCS strategies is to capture industrial CO2 emissions and inject them into the oceanic sediments to be stored as CO2 hydrates. However, the success of this technique depends on a few key factors such as the type of sediments where CO2 is injected, the kinetics of CO2 hydrate formation and dissociation, the accuracy of the models for prediction of formation kinetics, and the CO2 hydrates morphology. So, in this first-gen work, a highly complex set of experiments was carried out to examine the CO2 hydrate formation and dissociation processes by injecting CO2 via injection tube into different size wet sediments, i.e., coarse (diameter: 0.5–1.5 mm), granules (diameter:1.5–3.0 mm) and dual-layered sand (coarse + granules), embedded inside high-pressure reactor as the artificial seabed. The experiments were carried out at 3.5 MPa at T = 1.5–2.0 °C with 500 ppm of the eco-friendly hydrate promotor (l-tryptophan). The images of morphological changes during hydrate formation/dissociation, the Scanning Electron Microscope analysis of the sediments, and the estimated water-to-hydrate conversations have been reported in this work. A novel mathematical four-parameter-based CO2 hydrate kinetics model was also developed. A set of 32,843 experimental data points was used to train a supervised machine learning algorithm using two parameters with the other two taken from published literature. The water-to-hydrate conversion was estimated and follows the order of dual-layered sand [88.26 (±4.62) %] > coarse [77.77 (±5.72) %] > granules [65.36 (±2.3) %]. The proposed ML-based model predicted the water-to-hydrate conversion with an Average Absolute Relative Deviation [%AARD] of 4.23–13.29 %. This work serves as a step forward in developing a sustainable hydrate-based oceanic carbon storage technology.

Full implicit simulator of hydrate (FISH) and analysis on hydrate dissociation in porous media in the cubic hydrate simulator

Natural gas hydrate is a promising strategic energy resource in marine and permafrost sediments. To precisely characterize the coupled Thermal-Hydraulic-Chemical (THC) process in hydrate reservoirs, a bona fide mathematical model with improved key parameters is needed. We developed a Full Implicit Simulator of Hydrate (FISH), a three-phase, four-component mathematical model, to simulate gas recovery from hydrate reservoirs. The experiment of methane hydrate formation and dissociation under depressurization via a single vertical well was executed in the Cubic Hydrate Simulator (CHS). FISH was employed to reproduce the experiment of hydrate dissociation in quartz sands. This study successfully obtains unified parameters that are suitable for the entire hydrate dissociation process. Simulation results of gas and aqueous production profiles and the temperature distribution agreed well with that in the experiment. The Mean Absolute Percentage Error (MAPE) of the simulated volume of gas produced was 2.845%. The mass conservation in the pressure vessel was confirmed by both experimental data and numerical simulation results. This numerical simulator can be applied to predict the behavior of hydrate-bearing-sediments in the laboratory or to evaluate the gas production potential from the marine or permafrost hydrate reservoirs.

Deformation characteristics on anisotropic consolidated methane hydrate clayey-silty sediments of the South China Sea under heat injection

Natural gas hydrate is a new energy source with huge reserves, and the carbon content of hydrates is twice the carbon content of all proven fossil fuels combined, but the natural gas hydrate exploitation involves solid-liquid-gas phases change, which could induce a potential geological and environmental risk. Accurate description of the deformation behavior of sediments during hydrate dissociation is the key to predict the long-term stability of hydrate reservoirs. Nowadays, related studies mainly focus on the deformation behavior of hydrate-bearing sediment without dissociation. In this study, the deformation behaviors of remolded cores during thermal dissociation under anisotropy stress states were studied. The results show that 1) hydrate dissociation can lead to sediment deformation, the deformation rate of the sediments during the process of hydrate dissociation is 3 orders of magnitude larger than that before the dissociation. 2) the sediments under larger effective confining pressure (burial depth) present less deformation. 3) the sediments under isotropic stress conditions exhibit smaller deformation than that under anisotropic stress conditions. 4) dynamic permeability evolution during hydrate dissociation process can lead to effective confining pressure changes of the sediment, which can exacerbate the deformation.

CO2-TBAB semi-clathrate hydrate dissociation behaviour in individual capsules: A new two-stage numerical model and parametric study

Gas hydrates have a wide implementation in the capture, storage, transport and utilisation of a range of gases, in which the dissociation kinetics is of great importance to gas transport and recovery efficiency. Encapsulation has been proven an effective technique to enhance gas–liquid mass transfer and thus improve gas hydrate formation kinetics. However, the dissociation behaviour of gas hydrate in individual capsules remains unknown. In this work, the dissociation kinetics of encapsulated CO2-TBAB semi-clathrate hydrates in different shapes are experimentally investigated under various operating conditions, and, for the first time, a two-stage numerical model is developed which integrates mass transfer, heat transfer and the intrinsic gas hydrate reaction kinetics to simulate the gas hydrate dissociation process. The effects of temperature, pressure, capsule volume and capsule geometry on gas hydrate dissociation kinetics are investigated. The results reveal that the proposed model is capable of capturing two distinct experimentally-observed dissociation stages, a rapid and subsequently slow stage according to the measured dissociation rate. Surface-to-volume ratio of the capsule and the dissociation driving force are the two main factors influencing the dissociation kinetics. The ring-shaped capsule exhibits the most efficient dissociation process due to its high surface-to-volume ratio and long transition time to the slow dissociation stage. This work enhances the understanding of gas hydrate dissociation behaviour in individual capsules and guides the manipulation of dissociation for efficient hydrate-based gas transport and recovery.

Analysis of Methane Hydrate Dissociation Experiment in a Pilot-Scale Hydrate Simulator by a Full Implicit Simulator of Hydrate

Behaviors of gas and water production from a gas hydrate reservoir are based on fully coupled Thermal–Hydraulic–Chemical (THC) processes in porous media. Studies using experiments and mathematical models could be improved in hydrate-bearing sediments in the laboratory. The experiment of depressurization-induced methane hydrate dissociation via a single vertical well was carried out in quartz sands in a pilot-scale hydrate simulator (PHS). The multi-stage hydrate dissociation process, including the free liquid release, well shutdown, depressurization, and constant pressure, was achieved by complex manual operation of the production well in the experiment. A full implicit simulator of hydrate (FISH), a four-component, three-phase mathematical model, was developed and employed to reproduce the hydrate dissociation experiment. The kinetics of the hydrate reaction, heat/mass transfer in porous media, and mass conservation in the pressure vessel were validated by the experimental results. The key finding of this study is the acquisition of a group of unified parameters in a suitable mathematical model that could clearly elucidate the hydrate dissociation process in all stages. The mean absolute percentage error (MAPE) values of the gas and aqueous production are, respectively, as low as 2.338 and 9.630%. The strong confidence of the accuracy of the numerical simulator has been built up after the analysis of the experiment and the numerical simulation in this study, which could be used to evaluate gas recovery from marine hydrate reservoirs.

Fast Formation of Hydrate Induced by Micro-Nano Bubbles: A Review of Current Status

Hydrate-based technologies have excellent application potential in gas separation, gas storage, transportation, and seawater desalination, etc. However, the long induction time and the slow formation rate are critical factors affecting the application of hydrate-based technologies. Micro-nano bubbles (MNBs) can dramatically increase the formation rate of hydrates owing to their advantages of providing more nucleation sites, enhancing mass transfer, and increasing the gas–liquid interface and gas solubility. Initially, the review examines key performance MNBs on hydrate formation and dissociation processes. Specifically, a qualitative and quantitative assembly of the formation and residence characteristics of MNBs during hydrate dissociation is conducted. A review of the MNB characterization techniques to identify bubble size, rising velocity, and bubble stability is also included. Moreover, the advantages of MNBs in reinforcing hydrate formation and their internal relationship with the memory effect are summarized. Finally, combining with the current MNBs to reinforce hydrate formation technology, a new technology of gas hydrate formation by MNBs combined with ultrasound is proposed. It is anticipated that the use of MNBs could be a promising sustainable and low-cost hydrate-based technology.

A molecular dynamics study on nanobubble formation and dynamics via methane hydrate dissociation

The formation condition of nanobubbles and its effect on the methane hydrate dissociation were studied using molecular dynamics (MD) simulations. To investigate the effect of liquid water proportion on the methane hydrate dissociation path and nanobubble formation conditions, two different initial configurations were built. Considering low liquid water proportion simulation, four main dissociation stages were identified, and nanobubbles formed when the methane supersaturation condition was met. During this period, hydrate dissociation rate decreases and fluctuates around zero, indicating that mass transfer limitation forms and hydrate cages undergo a long-term disappearance and rebuilding process. Nanobubbles can form in two distinct regions: the liquid water region and the final hydrate slice region. Hydrate dissociation rate increased after the first nanobubble formed, which broke the mass transfer limitation. Small nanobubbles formed at the end of the hydrate dissociation process also contributed to the final hydrate slice collapsing by shortening the diffusion distance of methane molecules to the gas phase. At the end of the simulation, only one nanobubble survived in the system with a mole percent of methane in water for two systems remaining at 0.4 and 0.9, respectively.

Development of an explicit pressure explicit saturation (EPES) method for modelling dissociation processes of methane hydrate

ABSTRACT Methane gas is a fossil clean fuel since the products of the combustion are only carbon hydrate and water. Methane hydrate is a potential source of methane gas. This ice-like methane source can be found in deep seafloors and permafrost regions, characterized by high pressure and low-temperature conditions. In this work, we simulate the process of methane hydrate dissociation by depressurization in a cylindrical sandstone core by means of a two-dimensional axis-symmetric model, focusing on the transport phenomena involved in the process. Our simulations indicate a first rapid dissociation phase due to depressurization itself, and a longer subsequent one due to the thermal exchange with the external environment. Our numerical results match well with experimental data found in the literature, without showing any significant pressure or temperature delay among different sections compared to other numerical studies.

Comprehensive effects of heat and flow on the methane hydrate dissociation in porous media

The dissociation of methane hydrate in porous media is a heat flow coupling process. In this paper, we established a heat flow coupling algorithm for hydrate dissociation. A core-scale hydrate dissociation model was established and was verified against a laboratory dissociation experiment. The evolutions of the key characteristics, such as the temperature, the energy, and the hydrate/ice saturations, were analyzed. The effects of heat conductivity and permeability on dissociation characteristics and gas production rate were studied. It is found that there are three different modes under the coordinate system of heat conductivity and the permeability of porous media. In the flow-controlling mode, the rate of hydrate dissociation is mainly related to the flow resistance. In the heat-controlling mode, the rate of hydrate dissociation is mainly related to heat supply. In the heat flow-coupling mode, both the increase in the permeability and the heat supply have positive effects on the increase in the hydrate dissociation rate. In addition, there are different hydrate dissociation front expanding characteristics for the different modes. This analysis of the dissociation mode improves the understanding of events associated with the hydrate dissociation process.

Numerical simulation of methane hydrate dissociation characteristics in microporous media using lattice Boltzmann method: Effect of fluid flow

A multi-phase multi-component lattice Boltzmann model for modeling the gas hydrate dissociation process is proposed, which takes into account the dissociation kinetics, gas-water migration, and heat-mass transfer processes. This model is validated by simulating the xenon hydrate dissociation process. Subsequently, the dissociation mechanism of methane hydrate in microporous media, the gas-water migration, and the effect of fluid flow on the dissociation are investigated by using the present model. The simulation results indicate that methane hydrate dissociation facing the inlet is faster than that away from the direction of inlet flow. Meanwhile, fluid flow promotes methane hydrate dissociation. In addition, the rapid dissociation process within the pore space may lead to a large amount of water production accumulation. Another noteworthy phenomenon is the observation of bubbles formed by liquid curling flows. Liquid curling is one of the reasons for bubble formation near the gas-liquid interface.