Over the last decade, our research team at Ohio State University has analyzed geophysical well logs in over 1000 petroleum industry wells for natural gas hydrate. This is the largest well log assessment for gas hydrate and includes a number of basins: the northern Gulf of Mexico, offshore Western Australia, the Norwegian Sea, the Barents Sea and the UK Atlantic Margin.

We find evidence for gas hydrate in nearly half of industry wells, indicating that hydrate is widespread in sediments on Earth’s continental margins. Hydrate typically occurs in discrete, cm to m-scale intervals with depth and is at relatively low concentration (~35% saturation or less in a hydrate bearing layer). In addition, we observe that most of these hydrate bearing layers are not near the base of hydrate stability.  

At most locations in our assessment, hydrate is not susceptible to current anthropogenic warming. However, our assessment lacks information about a crucial location on continental margins because this interval is not typical measured by industry well logs: the updip edge of hydrate stability. The updip edge of hydrate stability (~300-500 m water depth) is a critical, largely uncharacterized zone where ocean warming can affect hydrate stability. Scientific ocean drilling is required to characterize the global gas hydrate occurrence and modern seafloor carbon flux along this sensitive boundary.

How to cite: Cook, A., Naim, F., Majumdar, U., Portnov, A., Jones, B., and Heber, R.: Widespread gas hydrate on Earth’s continental margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10226, https://doi.org/10.5194/egusphere-egu24-10226, 2024.

Gas hydrate (GH) formation and dissociation in natural systems is a complex, multi-process phenomenon controlled by local pressure-temperature-salinity (p-T-s) conditions and availability of methane gas. Our recent findings based on detailed analyses of GH systems using high fidelity multi-physics numerical model suggest that the long-term stability of the natural gas hydrate systems is not straightforward. On time scales ranging from hundreds to hundred of thousands of years, natural gas hydrate systems are able to develop, so-called, periodic steady-states characterized by a cyclic growth and dissolution of gas hydrate layers as well as a free gas migration through the gas hydrate stability zone (GHSZ). In this presentation, we show how these new results directly affect the estimates of global GH inventories and how they can be used to investigate the development of multiple bottom simulating reflectors (BSRs), slope failures, pockmarks, and gas migration pathways observed in the geological records that may have occurred spontaneously due to the internal system dynamics (i.e. gas hydrate cyclicity).

On a global scale, we have quantified the potential effect of the periodic states expressed as a new uncertainty measure that sets the hard limits on the predictability of present-day gas hydrate inventories through steady-state analysis. On a regional scale, focused on high-latitude locations, we present a combination of system parameters leading to periodic states and provide uncertainty quantifications on the gas hydrate system stability and faith. In that context, we discuss the relation between the time-periods of the cyclic states and the external triggers affecting gas hydrate systems in the Arctic (e.g. anthropogenic warming, sea level changes, glacial- interglacial cycles, etc.).

Keywords: methane cycle, global carbon budget, natural gas hydrate systems, periodic steady-states

How to cite: Burwicz-Galerne, E. and Gupta, S.: The influence of gas hydrate cyclicity on global and regional gas hydrate inventories, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18754, https://doi.org/10.5194/egusphere-egu24-18754, 2024.

During the last 1 Ma in the Canadian Arctic, permafrost and permafrost-associated gas hydrates formed extensively due to mean annual subaerial temperatures of approximately -20°C. Following the last glaciation, a marine transgression occurred and former terrestrially exposed shelves became inundated, resulting in present submarine bottom water temperatures around -1°C. Relict submarine permafrost and gas hydrates in the Canadian Beaufort Sea are still responding to this thermal change resulting in their ongoing degradation. Thawing of permafrost and destabilisation of permafrost-associated gas hydrates can release previously trapped greenhouse gases and can lead to even further gas hydrate dissociation with important implications for the global climate. However, both the extent of the submarine permafrost and the permafrost-associated gas hydrates are still not well known. In this study, we use marine multichannel seismic data to model the base of permafrost from the depth of the base of the gas hydrate stability zone. From this depth, we estimate the theoretical gas hydrate dissociation temperature, which allows us to model the depth of the thermal base of permafrost (0°C isotherm). The base of permafrost we modelled correlates with the lower boundary of a diffuse zone of high diffractivity in seismic data suggesting the presence of ice-bearing permafrost. These results combined show that the base of permafrost still extends close to the shelf edge indicating less permafrost retreat than previously suggested. Our study provides a different approach to accessing the current depth and extent of submarine permafrost on the outermost Canadian Beaufort Shelf.

How to cite: Grob, H., Riedel, M., Krastel, S., Preine, J., Duchesne, M. J., Jin, Y. K., and Hong, J. K.: Modelling the base of submarine permafrost in the Canadian Beaufort Sea from seismic data and the depth of the gas hydrate stability zone , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15668, https://doi.org/10.5194/egusphere-egu24-15668, 2024.

This work outlines the theretical and field activities conducted under the Bulgarian Science Fund Project GEOHydrate: Geothermal evolution of marine gas hydrate deposits - Danube paleodelta, Black Sea. The purpose of this research is to enhance our understanding and perspectives of the study the connection between marine gas hydrate deposits formation and the measured in situ heat flow in seafloor sediments.

The aim of the GEOHydrate project is to prove the hypothesis about the existence on the seafloor of measurable temperature and heat flow (T&HF) anomalies above gas hydrates deposits (GHDs) and the possibility to restore the 4D-process of GHDs growth from these anomalies.

GEOHydrate data include 2D and 3D seismic and CSEM; in situ heat flow; hydro- and geo-physicochemical measurements; scientific drilling and logging. They are results from the projects BLASON, ASSEMBLAGE, GHASS and specially developed tools and methods for GHDs research from the German projects SUGAR I-III. The applied methods include seismic data interpretation; basin analysis; forward and inverse geothermal problems. The new heat flow approach continues to develop in the EU project DOORS with new cruise data and interpretation. Expected practical results are contribution to direct methods for GHDs search, resource estimation with a high signal-to-noise ratio, and a reduction in the future production costs from proper planning and reducing the number of production wells.

Results contribute to mitigating the effects of 3 modern global threats - climate change, clean air, and the cost of energy. European GHDs production is the most prospect and important for Bulgaria and Romania.

Acknowledgments: This work was supported by:

• Bulgarian Science Fund project KP-06-OPR04/7 GEOHydrate “Geothermal evolution of marine gas hydrate deposits - Danube paleodelta, Black Sea” (2018-2023);
• European Union project 101000518 DOORS: Developing Optimal and Open Research Support for the Black Sea (2021-2025).

How to cite: Vasilev, A., Pehlivanova, R., and Genov, I.: Danube Fan gas hydrates: GEOHydrate project results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16228, https://doi.org/10.5194/egusphere-egu24-16228, 2024.

Natural gas hydrates represent a significant and widely distributed potential energy source globally. Furthermore, hydrates are also considered a possible carbon capture and storage method in the permafrost and deep ocean sea areas. Hydrate morphology is critical in determining the sediments' flow properties and production/storage efficiency. However, the dynamic morphology remains unclear, especially in the microscale. This study was performed by MH21-S and funded by the Ministry of Economy, Trade and Industry, and we used our self-invented micromodels (micron level) for hydrate formation in an air bath of 1 °C for several months. Meanwhile, the state-of-the-art high-resolution microscope was used to detect the dynamic morphology of hydrate formation and dissociation. The result showed that the hydrate growth mechanism could be divided into four stages due to different driving forces: hydrate fingering formation, Ostwald ripening phenomenon, hydrate contraction, and heterogeneous hydrate dissociation processes. In the first stage, the hydrate fingering formation process consistently occurs from the inlet to the outlet area, and the fingering process stops after several days. In the second stage, the Ostwald ripening phenomenon was detected in the microscale for the first time. Smaller hydrate particles first dissolved and then redeposited onto larger hydrate particles, which is a spontaneous process. In the third stage, the surface area of hydrates tends to reduce to reach a more stable phase, resulting in the hydrate contraction. Finally, manual temperature increases induce heterogeneous hydrate dissociation. Our study aims to enhance the understanding of hydrate behaviors in sediments over an extended period.

How to cite: Xu, Z. and Konno, Y.: Dynamic morphology of clathrate hydrates in porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9891, https://doi.org/10.5194/egusphere-egu24-9891, 2024.

Natural gas hydrates are known to exist in vast quantities beneath the permafrost and deep-sea sediment layers worldwide, transcending national borders, making them a promising future energy resource. While test productions have been conducted by a few countries such as Japan, China, and the United States, a commercially viable production method has yet to be established. The technologies developed so far have limitations, as laboratory-scale experiments and computational models often fail to accurately predict production behavior in actual field conditions. To achieve reliable predictions of production patterns, it is crucial to understand the changes in phase distribution within hydrate-bearing sediment layers and the corresponding multiphase fluid behavior. This study utilizes low-field Nuclear Magnetic Resonance (NMR) to quantitatively analyze phase distribution, saturation, and pore occupancy changes within rock samples during hydrate formation and dissociation processes. Particularly, experiments on hydrate formation and dissociation, along with NMR signal analysis, were conducted under conditions where water is abundant to investigate the role and influence of excessive water. In cases of high initial water saturation (presence of movable water), it was observed that the phase saturation distribution during hydrate formation becomes heterogeneous due to water migration in an unexpected manner. During the depressurization-driven dissociation process, a quantifiable increase in water saturation due to dissociated water was observed, revealing the occurrence of hydrate reformation even during the dissociation process. This research provides a methodology and analytical data to understand phenomena that are challenging to predict during hydrate formation and dissociation processes.

How to cite: Ahn, T., Lee, J., and Park, C.: Quantitative Analysis of phase saturation distribution during hydrate formation and dissociation under high water saturation condition using low-field NMR, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14348, https://doi.org/10.5194/egusphere-egu24-14348, 2024.

On many marine continental slopes, gas hydrate has been observed filling fractures in marine muds.  Fracture filling hydrate likely forms because the pore size of clays is small, and therefore, hydrate can only form in secondary porosity; some scientists have suggested the process of hydrate formation causes these fractures to form. On borehole image logs, these fractures were found to have high angles and form in 3D planes. While the plane is filled with hydrate, the overall bulk concentration of hydrate can be quite low. In X-ray computed tomography (XCT) images, similar high angle planar fractures have been found that cut through whole round core. Typically, these fractures appear to have diffuse, wispy edges in comparison to other fractures that form due to core expansion or core collection. 

We have found new, smaller 3D planer fractures that are likely the initial stages of hydrate fracture formation. These hydrate-filled fractures range in lengths from around 10 – 400 mm with widths ranging from 0.5 - 15 mm. The fractures tend to be well oriented, having a high dip angles (>40°) and going through the whole core on a plane. The wispy, diffused edges suggest sediment displacement due to the hydrate formation process and are distinctly different than other fractures seen in the XCT data. The fractures must be unconnected to any other break in the sediment, existing solely as a fracture with a high dip angle, with diffused edges.

In New Zealand, IODP Site 1517, we found that these specific fractures appear near the sulfate-methane transition zone (SMTZ). We hypothesize that if more sediment cores and XCT data were collected through and close to the SMTZ, more similar small fractures would be imaged, potentially indicating nascent gas hydrate formation.

How to cite: Martin, S., Brunet, M., and Cook, A.: Small fractures in marine muds indicating nascent hydrate formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12146, https://doi.org/10.5194/egusphere-egu24-12146, 2024.

Molecular and stable isotopic compositions of light (C₁–C₃) hydrocarbons in sediments provide information on their formation pathways and postgenetic alterations. In 2018, gas hydrate-bearing sediment cores and borehole logging data were collected with R/V SONNE (cruise SO266) and the seafloor drill rig MARUM-MeBo200 at two sites off SW Taiwan (Bohrmann et al., 2023). The two sites are located on the passive continental margin and on the tectonically active convergent margin in the northern part of the South China Sea (SCS). Geophysical surveys have demonstrated the presence of hydrates at both sites as well as the base of the hydrate stability zone at ∼400 and 450 meters below seafloor (mbsf), respectively (Berndt et al., 2019; Bohrmann et al., 2023). At the passive margin, holes were drilled to a depth of ∼126 mbsf at the southern summit of Formosa Ridge (SSFR, ∼1,140 m water depth). A depth of ~144 mbsf was reached at Four-Way Closure Ridge (FWCR, ~1,320 water depth) on the active margin. Macroscopically, no hydrates were detected in recovered cores from either site, but hydrate-related proxies unequivocally demonstrated the in-situ presence of hydrates. For example, signals in sediment electrical resistivity detected during well logging correlated with anomalies in sediment temperature and pore water chloride concentrations detected in cores. Whereas two hydrate-bearing intervals were identified on SSFR (∼13–39 mbsf, ∼98–120 mbsf), a single interval was found on FWCR (∼65–120 mbsf).
Considerable variations in relative hydrocarbon concentrations expressed as C₁/(C₂–C₃) values were observed in gas accumulated in voids in the cores from each site. C₁/(C₂–C₃) values <10.000 in the hydrate-bearing sections, which contrast with values ranging between 10.000 and 25.000 in sections lacking hydrates, indicate that ethane (C₂) and to a lesser extent propane (C₃) are enriched during hydrate precipitation. Molecular fractionation is also observed for CO₂, which is strongly depleted in the hydrate-bearing sections. The δ¹³C- (–79 to –69‰) and δ²H- (–197 to –187‰) values of methane (C₁) indicate that microbial carbonate reduction is the major source of light hydrocarbons (Milkov & Etiope, 2018) at both sites. Based on pore water sulfate and methane concentrations, the zone of the microbially-mediated sulfate-dependent anaerobic oxidation of methane was identified at a depth of ~10–12 mbsf at both sites. Preferential consumption of C₁ in this zone is indicated by low C₁/(C₂–C₃) values. The process also resulted in depletions of C₁ in ¹³C and ¹H (δ¹³C-C₁ as low as -100‰, δ²H-C₁ as high as -179‰ at 18 mbsf at FWCR) as reported from other regions (e.g., Nankai Trough off Japan; Riedinger et al., 2015).
Our results show that physical fractionation and bio(chemical) transformation of individual light hydrocarbons can significantly change the molecular and isotopic composition of upward migrating gases. Therefore, the composition of shallow gas does not necessarily reflect that of the gas in the deeper subsurface, for example as bound in capacious hydrate reservoirs. The cores from the SCS are excellent for studying how hydrate occurrences and microbial transformation lead to alteration of gas composition.

How to cite: Pape, T., Tu, T.-H., Lin, S., Berndt, C., Wallmann, K., Tseng, Y., Freudenthal, T., and Bohrmann, G.: Gas hydrate precipitation and microbial transformation affect the composition of gases migrating through sediments drilled off SW Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16042, https://doi.org/10.5194/egusphere-egu24-16042, 2024.

By using X-ray computeted tomography(XCT), low-field nuclear magnetic resonance(NMR), N₂ gas adsorption(N₂GA) method, the microscopic pore system of hydrate-bearing sediments in  KG Basin was comprehensively characterized. Results shown that the pore types are complex, with diverse pore geometry, poor connectivity, foraminiferal shells provide certain pores, 4-20μm micropores contribute the most to permeability. For the lacking of measuring closed pores by N₂GA leads to a significant difference in the total pore volume compared with NMR results.

Through monitoring the phase transition process in pores under temperature changes through NMR, the intensity value of the first peak signal of CPMG is collected, meanwhile the pure water signal is calibrated to calculate the unfrozen water content and pore size distribution. The results indicate that the water signal inside the macropores is constantly increasing, significantly weaker than in the micropores; the middle peak values corresponding to the mesopores are disorferly. Analysis shows that water migration occurs within the mesopores, the process of ice melting into water initial occurs in smaller pores.

How to cite: Guan, W.: Multi-scale characterization for pore systems of  hydrate-bearing reservoir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20561, https://doi.org/10.5194/egusphere-egu24-20561, 2024.

Climate change is mainly monitored at the Earth's surface. However, it is well known that as part
of ongoing climate change, ocean circulation is also changing, and therefore the ocean floor is
also subject to temperature changes.
In this study, the depth of the global methane hydrate stability zone was assessed by analyzing its
changes over the period from 1993 to 2018 to investigate the effect of climate change on the
stability of methane hydrates.
Indeed, seafloor sediments are often permeated by a methane hydrate phase, the stability of
which depends on the pressure and temperature field, among other parameters, and any changes
in temperature conditions near the seafloor can bring the methane hydrate into unstable
conditions.
The data needed for the assessment of methane hydrate stability were obtained from The Global
Ocean Physics Reanalysis data set (GLORYS12V1), produced under the European Copernicus
Marine Environment Monitoring Service (CMEMS), and GEBCO- The General Bathymetric Chart
of the Oceans. The data were then processed with original data processing software developed in
Fortran and Python languages.
A quantitative estimate of the amount of methane released into ocean masses by the dissociation
of methane hydrate in shallow sediments over the period under consideration was also obtained.
The release of large amounts of methane could have an impact on submarine geological hazards,
such as submarine landslides, and the eventual reaching of the atmosphere by methane would
reinforce ongoing climate change.

How to cite: Riccucci, L., Camerlenghi, A., Salon, S., and Tinivella, U.: Temporal variability of the stability field of methane hydrates in the oceans, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21623, https://doi.org/10.5194/egusphere-egu24-21623, 2024.

Methane hydrates are the most abundant clathrates found in the environment, predominantly in the permafrost and marine continental margins. As such, they consitute an energy resource, a concern for climate change, as well as a potentially significant source of carbon for microorganisms. However, relatively little is known about the way that these microorganisms interact, if at all, with methane hydrate deposits in their environment. Recently, a porin produced by a marine methylotroph (Methylophaga aminisulfidivorans) was found to promote hydrate formation in conditions mimicking that of the seafloor. A specific peptide sequence (TAFDGGS) was shown to be at least partially responsible for this behaviour. However, the exact physico-chemical mechanisms underlying such effects are still unclear.

Our research employed a dual methodology, integrating experimental procedures with molecular dynamics simulations to answer the question of how naturally occurring peptides can influence methane hydrate formation. Initially, laboratory experiments were conducted to observe the kinetics of methane hydrate formation in the presence of the selected natural peptide (TAFDGGS) and the traditional hydrate promoter: sodium dodecyl sulfate (SDS). Methane hydrate formation from deionized water served as a reference. Parameters such as rate of formation, induction time and total gas consumption were meticulously recorded and analysed. In parallel, molecular dynamics simulations of the hydrate formation process with and without the peptide were carried out. The careful analysis of the interactions between water, methane and the peptide provided molecular-level insights on how peptides can influence the nucleation and growth of methane hydrate clusters. Our results indicate that the natural peptide exhibits a distinctive promoting effect on the formation kinetics of methane hydrates. However, the mechanistic hypothesis that the promotion effect is achieved by providing more nucleation sites was ruled out by comparison with the reference groups. Instead, the results suggest a more complex biocatalytic effect on hydrate kinetics.

These findings suggest a potential for peptides as eco-friendly alternatives to traditional chemical promoters in methane hydrate research and provide valuable insights into the design of more efficient and sustainable bio-based promoters. More fundamentally, this study lays a solid foundation for our understanding of the interactions between peptides and hydrates in nature and paves the way for further research on the role of proteins or microorganisms on hydrate deposits.

How to cite: Pan, M., Radola, B., Allen, C. C. R., and English, N. J.: The Pioneering Role of Natural-Occurring Peptides on Methane Hydrate Formation—Insights from Experiments and Numerical Simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18603, https://doi.org/10.5194/egusphere-egu24-18603, 2024.

Given the scale and urgency of the climate crisis, the exploration of innovative approaches for greenhouse-gas CO₂ capture and sequestration is imperative. This hinges on capturing of CO₂ emissions from sources, and storing it into other long-lived, stable carbon “pools” or “sinks”, such as in the form of gas hydrates. Being crystalline solids, gas hydrates have the ability to store gas effectively therein –with gas molecules “imprisoned” in cavities within an otherwise ice-like lattice. To address the limitations of hydrate-based methods for carbon capture, such as stability, scalability, and environmental impacts, gas-nanobubble technology may be integrated into hydrate formation to enhance the efficiency and viability of gas-hydrate formation. Nanobubbles (NBs) have been confirmed to accelerate gas-hydrate crystallisation through the so-called memory effect. However, the mechanism of interactions between NBs and hydrate crystals has not been fully addressed. It is also vital to investigate the optimal conditions for hydrate formation in the presence of NBs for higher stability and scalability.

In this study, a novel method, combining NBs and gas hydrates to enhance the capturing of CO₂, is reported. It aims to demonstrate the effects of NBs on hydrate-formation kinetics, and reveals the mechanism of their interactions during the hydrate-crystallisation process by an integration of laboratory experiments and molecular dynamics simulations. NBs were generated by external electric fields with CO₂ gas in deionized water. By controlling the processing time and applied voltage, different size and concentration of NBs were expected. DLS measurements were applied to characterise the generated NBs. The kinetic properties of CO₂ hydrate formed by NBs solution were analysed experimentally. Numerical dynamics simulations were also applied to simulate the hydrate-formation process in the presence of CO₂ NBs with different concentrations. These modelling efforts help in predicting the behavior of the system under different conditions. The simulation results revealed that throughout the growth process, the size and shape of NBs changed, progressively reducing in size. It appears that the hydrate clusters absorbed gas molecules from the surrounding gas clusters, leading to the disappearance of the NB in some systems. These bubble remains in the vicinity of the hydrate interface and supplies CO₂ for the hydrate growth. When these bubbles reached a critical size where stability was compromised, they collapsed, resulting in a localized increase in CO2 concentration in the aqueous phase, further promoting hydrate growth. The interaction between water and CO₂ molecules increased as the hydrate surface absorbed the gas molecules from the solution and consumed them to form new hydrate cavities. Therefore, CO₂ molecules have less preference to interact with each other and thus the gas clusters were shrinking during the simulation.

The outcome of this study deepens the understanding of nanobubble dynamics and addresses the critical role of nanobubbles in CO₂ hydrate-crystallization processes - directly contributing to the mitigation of climate-change impacts. 

How to cite: English, N., Naeiji, P., and Pan, M.: Mitigating climate change: investigating the synergistic effects of nanobubbles and gas hydrates for enhanced carbon capture, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16492, https://doi.org/10.5194/egusphere-egu24-16492, 2024.

Natural gas hydrates form at elevated pressure and low temperatures in the presence of sufficient quantities of gas and water and have therefore been discovered on all continental margins and in permafrost regions. In the marine hydrate-bearing sediments, gas hydrates, depending on their content, can transform a loose sediment into a consolidated rock with a strongly increased strength. In permafrost regions the hydrate stability zone can extent deep into the ice-bearing permafrost and, therefore, both, ice and hydrate can consolidate the sediment. However, the strength of methane hydrate is much higher than that of ice, which behaves much more ductile. Consequently, the resulting strength of a sediment, containing both components, strongly depends on the ice to hydrate ratio. Conversely, the decomposition of natural gas hydrates in marine or permafrost sediments leads to a reduction in the mechanical strength of the host sediment. In addition, the release of gas can create overpressure in the pore spaces, reducing the effective stress and leading to instabilities in the sediment structure.

Since both continental margins and permafrost regions are used by humans for various activities that largely depend on the mechanical stability of the sediments, knowledge of the main factors and processes that determine the stability of weakly consolidated sediments is crucial. Both the thawing of ice and the decomposition of gas hydrates in permafrost soils lead to a change in the geo-mechanical properties of the host sediment. The residual and peak shear strengths of ice- and hydrate-bearing sediments were investigated using a ring shear cell developed at the GFZ. Based on literature data and our results, we discuss the dependence of the geo-mechanical properties of sediments on ice and hydrate saturation and the possible consequences if their proportion diminishes.

How to cite: Spangenberg, E., Cook, A., Schicks, J., and Heinig, F.: A diminishing stabilizer? Studies on the influence of ice and gas hydrates on the geo-mechanical properties of sediments., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12671, https://doi.org/10.5194/egusphere-egu24-12671, 2024.

Natural gas hydrates are crystalline compounds that are formed from hydrogen-bonded water molecules and gas molecules. They mainly contain climate-active CH₄, but also other light hydrocarbons, CO₂ or H₂S They exhibit a high sensitivity to variations in temperature and pressure, mainly driven by environmental changes. The oceanic or atmospheric warming resulting from climate change may trigger the decompositions of hydrates, potentially releasing significant amounts of CH₄. To assess the potential risks associated with CH₄ release from destabilized hydrate deposits, a precise understanding of the dissociation behaviour of gas hydrates becomes crucial.

In this study, a systematic investigation on the dissociation process of sI CH₄ hydrates, sII CH₄+C₃H₈ hydrates, and sII multi-component CH₄+C₂H₆+C₃H₈+CO₂ mixed hydrates was reported. We employed a combination of experimental and molecular dynamics (MD) simulations to provide a more nuanced understanding of the hydrate dissociation behaviours, which primarily shed light on the molecular aspects. The dissociation was induced through thermal stimulation to mimic climate warming. Both in situ and ex situ Raman spectroscopic measurements were performed continuously to characterize the hydrate phase. Throughout the dissociation process, hydrate composition, surface morphology, and the large-to-small cavity ratios were determined.  MD simulations were carried out under similar conditions, providing advanced insights and perspectives that couldn't be readily extracted from experimental observations alone.

Both experimental and simulation outcomes indicate that intrinsic kinetics likely govern the early stage of hydrate dissociation. A significant development in the dissociation process is the hindrance caused by the formation of a quasi-liquid or amorphous phase at the surface of the hydrate particles after the breakup of the outer layer of hydrate cavities. The unstable (partial) hydrate cavities that form within this quasi-liquid phase are oversaturated with gas molecules. Consequently, gas hydrates undergo a cycle of decomposition-reformation-continuing decomposition until the crystal eventually disappears. With decomposition dominating the process, both experimental and numerical simulation results demonstrate that the breakup of large cavities (5¹²6²) is faster than that of small ones (5¹²) in sI hydrates. Conversely, a faster breakdown of small 5¹² cavities in sII hydrates is observed. Additionally, during the dissociation process of sII CH₄-C₃H₈ hydrate, the cavities occupied by CH₄ preferentially collapse compared to those filled with C₃H₈. Similarly, over the dissociation of multi-component hydrate, cavities filled with CH₄ exhibit a preferential collapse compared to those filled with C₃H₈, C₂H₆, and CO₂.  These findings show the complexity and differences in the dissociation behavior of natural gas hydrates depending on their composition and structure and can therefore make an important contribution to an accurate assessment of CH4 release from destabilized hydrate deposits in response to climate change.

How to cite: Schicks, J., Naeiji, P., and Pan, M.: Systematic Investigation of Natural Gas Hydrate Dissociation Processes with Regard to Global Warming, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17331, https://doi.org/10.5194/egusphere-egu24-17331, 2024.