Gas Hydrate Dissociation Research Articles

Effects of Crystal Facets of Quartz on the Formation and Dissociation of Natural Gas Hydrates

Natural gas hydrates are non-stoichiometric crystalline compounds composed of natural gas and water, typically found in the pore spaces constructed by minerals. Mineral crystals exhibit significant variations in surface properties among different crystal facets. Despite the importance of these mineral crystal facets, previous studies have not reported their influence on natural gas hydrates. To address this gap, we focused on quartz, a vital component of hydrate reservoirs, and studied the process of natural gas hydrates formation and dissociation on its distinct crystal facets. In our investigation, we simplified pores as narrow gap spaces between two parallel quartz substrates, and captured the entire process with a microscope. The results indicate that the formation and dissociation of natural gas hydrates are notably influenced by the distinct crystal facets of quartz. The influences of quartz crystal facet on the hydrate formation are primarily attributed to two factors, wettability and hydroxyl concentration of quartz crystal facet. We have also revealed the mechanism of how quartz crystal facet influences the hydrate dissociation. This research provides a fundamental understanding of how mineral crystal facets influence the hydrate formation and dissociation, offering a novel perspective for the design of processes for extracting hydrate.

Effect of Isotropic and Anisotropic Permeability on Gas Production Behavior of Site NGHP-01-10D in Krishna-Godavari Basin

This study reports an investigation into both isotropic and anisotropic permeability effects on gas production behavior during depressurization-induced natural gas hydrate dissociation at site NGHP-01-10D in the Krishna-Godavari basin. Numerical simulations were performed on a reservoir-scale model incorporating a single vertical well, examining different scenarios of permeability ratios (rrz). The investigation assessed gas and water production rates, cumulative production volumes, the gas-to-water ratio, and the spatial distribution of reservoir parameters throughout a production duration of 3 years. The findings indicate that permeability anisotropy has a substantial impact on hydrate dissociation and gas recovery. For rrz > 1, horizontal pressure propagation was promoted and gas production increased. For example, at t = 1100 days, the total gas production improved from 7.88 × 105 ST m3 for rrz = 1 to 55.9 × 105 ST m3 for rrz = 10. For rrz < 1, vertical pressure propagation resulted in higher water production with concomitantly lower rates of gas production rates. Spatial distribution analysis revealed that higher rrz values led to more extensive radial propagation of pressure drop, temperature decrease, gas saturation increase, and hydrate dissociation. The study concludes that higher horizontal permeability enhances depressurization effects, resulting in higher gas production rates and more favorable gas-to-water ratios.

Molecular insights into methane hydrate dissociation: Role of methane nanobubble formation.

Understanding the underlying physics of natural gas hydrate dissociation is necessary for efficient CH4 extraction and in the exploration of potential additives in the chemical injection method. Silica being "sand" is already present inside the reservoir, making the silica nanoparticle a potential green additive. Here, molecular dynamics (MD) simulations have been performed to investigate the dissociation of the CH4 hydrate in the presence and absence of ∼1, ∼2, and ∼3nm diameter hydrophilic silica nanoparticles at 100bar and 310K. We find that the formation of a CH4 nanobubble has a strong influence on the dissociation rate. After the initial hydrate dissociation, the rate of dissociation slows down till the formation of a CH4 nanobubble. We find the critical concentration and size limit to form the CH4 nanobubble to be ∼0.04 molefraction of CH4 and ∼40 to 50 CH4 molecules, respectively. The solubility of CH4 and the chemical potential of H2O and CH4 are determined via Gibbs ensemble Monte Carlo simulations. The liquid phase chemical potential of both H2O and CH4 in the presence and absence of the nanoparticle is nearly the same, indicating that the effect of this additive will not be significant. While the formation of the hydration shell around the nanoparticle via hydrogen bonding confirms the strength of interactions between the water molecules and the nanoparticle in our MD simulations, the contact of the nanoparticle with the interface is infrequent, leading to no explicit effect of the nanoparticle on the dynamics of methane hydrate dissociation.

Thermodynamic modelling of gas hydrate dissociation conditions in porous medium in the presence of NaCl/methanol aqueous solution

AbstractDue to the growing significance of the existence of gas hydrates in natural media like the ocean floor/permafrost regions and the extraction of natural gas from hydrate reservoirs using thermodynamic hydrate inhibitors, investigating the dissociation of gas hydrates in porous media in the presence of inhibitors is crucial. This work examines a broad range of laboratory data on the dissociation conditions of gas hydrates in the porous mediums when salt/alcohol aqueous solutions are present. The temperature of gas hydrate dissociation in the presence of pure water is calculated using the van der Waals–Platteeuw solid solution theory. The water activity in the porous medium is then calculated by taking into account a number of variables, including the radius of the porous medium, molar volume, shape factor, wetting angle, and surface tension. The Pitzer and Margules activity coefficient models are used to determine the water activity in the presence of salt and alcohol, respectively. Lastly, the gas hydrate dissociation temperature in a porous medium in the presence of salt and/or alcohol aqueous solution is determined by combining Piereon's model with an enthalpy‐based correlation that was proposed by Azimi et al. The selected package can consistently correlate the gas hydrate dissociation conditions in a porous medium in the presence of alcohol or salt aqueous solution. The average absolute deviation (AAD) of 0.67 K for the whole data bank (90 experimental data points) shows the precision of the model.

The formation of tubular seep carbonate deciphered from mineralogical and geochemical characteristics: an example from the South China Sea

As a special type of seep carbonate, the many details concerning the formation mode and mechanism of tubular seep carbonates are rarely reported. Here, new geochemical and mineralogical data regarding tubular seep carbonate (SQW-65) are reported. Sample SQW-65 had anomalously negative δ13C values and positive δ18O values, which suggested the dissociation of gas hydrate. Additionally, almost all the sub-samples showed no Ce anomaly (Ce/Ce*average = 0.93), with obvious U enrichment (21.3< UEF <240.3), which indicates that the studied tubular seep carbonate was formed in an anoxic environment. Subsequently, the formation process of the studied tubular seep carbonate is further discussed according to the variability of mineralogical and geochemical characteristics from the rim to the core of the tubular formation. In the early stage of the studied tubular seep carbonate (periphery), owing to the influence of terrigenous components, the quartz and Ti content and Y/Ho ratio were high. However, with the formation of the periphery, the influence of terrigenous components was gradually weakened. In addition, from the rim to the core, the carbon and oxygen isotope values showed a “covariation” coupling relationship, an enrichment of U, and a reduction in total rare earth element content. This is because as the outer wall thickens and the internal fluid channel narrows, the intensity of the sulphate-driven anaerobic oxidation of methane and the associated precipitation rate of carbonate also increase.

Postglacial ocean methane release from the northern South China Sea

Methane release into seawater and the atmosphere as a result of cold seepage activity is a sensitive indicator of global environmental change during the last glacial period. However, the link between postglacial ocean methane escape and possible increases in atmospheric methane concentration remains unclear, which hinders the evaluation of methane impact on climatic variability. In this study, lipid biomarkers were analyzed on samples from the Shenhu area in the South China Sea to reconstruct the marine gas hydrate variability since the last glacial time. The reconstructed methane release during the cool Last Glacial Maximum and Younger Dryas agreed well with previous findings. Interestingly, our results identified a pronounced methane outgassing at the end of Heinrich 1, which was likely triggered by the abrupt increase in intermediate water temperature. The occurrence of this gas hydrate dissociation before the drastic rise in atmospheric methane during Bølling-Allerød implied that the change in the gas hydrate reservoir could likely indirectly contribute to the initiation of the warming event, though more global evidence needs to be provided in the future.

Application of time domain reflectometry to triaxial shear tests on hydrate-bearing sediments

Various triaxial shearing apparatus are used to quantify mechanical properties of hydrate-bearing sediments which are basically required to the assessment of risks posed by dissociation of natural gas hydrates. However, the key factor, hydrate saturation, has not been well measured during triaxial shearing tests. This study aims to show how a time domain reflectometry (TDR) method nondestructively measures hydrate saturation for triaxial shear tests on hydrate-bearing sands. Hydrate saturation is determined based on the difference of volumetric water contents measured by using a flexible TDR probe with two rods after calibration. The results suggest that values of hydrate saturation acquired by the TDR method are accurate, and the flexible TDR probe can monitor the kinetic process of hydrate formation and avoid any reinforcement effects on triaxial shearing properties of test specimens.

Fate of Nanobubbles Generated from CO2–Hydrate Dissociation: Coexistence with Nanodroplets—A Combined Investigation from Experiment and Molecular Dynamics Simulations

The evolution of CO2 nanobubbles generated by gas–hydrate dissociation is comprehensively studied in this research, employing a synergistic approach that combines laboratory experiments and molecular dynamics simulations. The results show that a higher concentration of nanobubbles can be observed in the early stages of hydrate dissociation, while smaller, thus‐generated, nanobubbles are less stable and prefer to amalgamate into larger bubbles through coalescence or Ostwald ripening. From the high Laplace pressure inside some nanobubbles as well as their higher local densities, they may transform into nanodroplets by densification fluctuations. Thus, the dynamic coexistence of nanobubbles and ‐droplets is confirmed from both experimental and simulation measurements. The number and size of the nanobubbles in the system affects the interaction between water molecules and their movements so that the water molecules diffuse faster upon this condition. The water–water interactions become more pronounced in the presence of nanobubbles and the hydrogen bond network is better preserved in the bulk. This study provides new insights into the microscale mechanisms of gas–hydrate dissociation and highlights the complex interactions between nanobubbles/ ‐droplets, and the aqueous environment after CO2–hydrate dissociation.

Effect of Surfactants on the Synthesis and Dissociation of Gas Hydrates

The synthesis and dissociation of methane hydrate and carbon dioxide hydrate were studied. Nonflammable gas hydrates can be used to extinguish flames in confined spaces. To increase the extinguishing efficiency, it is necessary to increase the dissociation rate (gas release rate) by using surfactant. The work investigates gas hydrates synthesized using sodium dodecyl sulfate (SDS). Experimental studies were carried out in wide ranges of surfactant concentration, the number of the stirrer revolutions and the initial water volume. To achieve the maximum rate of synthesis and dissociation, optimization of the specified parameters was performed. The influence of the key parameters on the dissociation rate was investigated experimentally and theoretically. The novelty of the work lies in solving a complex of interrelated tasks on the synthesis and dissociation of gas hydrate. It is shown that in order to achieve the maximum dissociation rate of carbon dioxide hydrate, it is necessary to optimize the following parameters: the diameter of the particles and their porosity, the porosity of the layer and the external heat flux.

The geomechanical response of the Gulf of Mexico Green Canyon 955 reservoir to gas hydrate dissociation: A model based on sediment properties with and without gas hydrate

Gas hydrate is commonly found concentrated in sand- and silt-rich reservoirs and these are thought to have great potential as an energy resource. To evaluate this potential, it is critical to understand their in-situ stress state and their behavior during production. We explore the geomechanical behavior of sandy silt sediments from a hydrate reservoir at Green Canyon GC 955, deep-water Gulf of Mexico without hydrate and compare these results to previous work on the same sandy silty sediments with hydrate present. Previous results from hydrate-bearing sediments at GC 955 using intact specimens show that the ratio of lateral to axial effective stress under uniaxial strain (K0) is strongly time-dependent and over long timescales approaches 1 (isostatic stress state). New results from sediments without hydrate using reconstituted specimens reveal that K0 is 0.51 and independent of time and stress. The reservoir without hydrate is approximately three times more compressible than with hydrate. In addition, we find that hydrate-free sediments have a normalized creep rate of Cα/Cc of about 0.028 at all stress levels, whereas hydrate bearing sediments exhibit a decrease in Cα/Cc with stress. We use these observations to present a new geomechanical model that describes how stress and porosity evolve during production of the hydrate reservoir. The key insight in our proposed model is that the sediment skeleton and gas hydrate phases share any applied external load in proportion to their relative stiffnesses. The model results predict that hydrate-bearing sediments are stiffer than gas hydrate-free sediments and that K0 reduces dramatically after gas hydrate dissociation, as is observed. At GC 955, a 5 MPa depressurization is needed to cause gas hydrate dissociation. This change in pore pressure increases the vertical and horizontal effective stresses from 3.8 to 8.8 MPa and 3.8–4.4 MPa, respectively. The dramatic vertical effective stress increase will cause significant compaction (7%) and perturb stresses near the wellbore. These experimental observations and the load-sharing model presented have the potential to underpin a new generation of hydrate reservoir simulation models, which may drive more effective production approaches.

An improved analytical model of effective thermal conductivity for hydrate-bearing sediments during elastic-plastic deformation and local thermal stimulation

As one of the crucial thermal properties controlling the dissociation of natural gas hydrate (NGH), effective thermal conductivity (ETC) should be precisely determined to improve the efficiency of NGH exploitation. But so far, most existing analytical ETC models of hydrate-bearing sediments could not accurately characterize the evolution of ETC. In this paper, an improved analytical model is derived for quantitatively revealing physical relations between ETC and various influencing factors during elastic-plastic deformation and local thermal stimulation processes, including hydrate saturation change, complex pore structures evolution, and hydrate occurrence patterns transition. The effectiveness of the proposed model is validated against available experimental data and compared with other existing models, then effects of various critical parameters on ETC are investigated. Results show that the porosity of hydrate-bearing sediments is accurately predicted during both loading and unloading processes, and the calculated ETC values under various conditions (effective stress, hydrate saturation, and temperature) are satisfactory with the test data. Contributions of elastic deformation and plastic deformation to ETC increments are quantitatively obtained. It is noteworthy that this proposed model is significant to reveal the evolution mechanisms of ETC, helping to accurately predict gas production and offer better plans for efficient NGH exploitations.

Confined Compressibility of Fine-Grained Marine Sediments with Cavities after Complete Dissociation of Noduled Natural Gas Hydrates

Confined Compressibility of Fine-Grained Marine Sediments with Cavities after Complete Dissociation of Noduled Natural Gas Hydrates

Dynamic accumulation of a high-grade gas hydrate system: insights from the trial production gas hydrate reservoir in the Shenhu area, northern South China Sea

The ultimate enrichment level and quantity of gas hydrate resources are influenced by the dynamic process of accumulation and preservation. High-resolution 3-D seismic data, logging while drilling (LWD), pressured coring, and in situ testing were used to characterize the dynamic accumulation and preservation of the trial production high-grade gas hydrate reservoir (HGGHR) in the Shenhu area. Through seismic variance analysis and ant-tracking, we found that newly identified mud diapir-associated faults with three development stages controlled the migration and accumulation of gas hydrate and shifted the base of the gas hydrate stability zone (BGHSZ), resulting in dynamic accumulation and dissociation of gas hydrates. The recognized double bottom simulating reflectors (BSRs) were concluded to have been formed due to the shift of the BGHSZ caused by the variational equilibrium conditions. The interval between the double BSRs was inferred to be a disequilibrium zone where gas recycling occurred, contributing to the coexistence of gas hydrates and free gas and the dynamic formation of the HGGHR. Multiple gliding faults formed within the GHSZ in the late period have altered the HGGHR and control the present thickness and distribution of the gas hydrates and free gas in the hanging wall and footwall. Under the influence of geothermal fluids and the fault system associated with the mud diapir, the HGGHR experienced dynamic accumulation with three stages, including early accumulation, medium-term adjustment, and late alteration and preservation. We conclude that four factors affected the formation, distribution, and occurrence of the HGGHR: the geothermal fluids accompanying the deep mud diapir below the reservoir, the dual supply of thermogenic gas and biogenic gas, the recycling of hydrate gas beneath the BGHSZ, and the post-gas hydrate faults developed within the GHSZ. A geological model illustrating the dynamic formation of the trial production HGGHR was proposed, providing a reference for future exploration of HGGHRs with a great production potential in deepwater settings.

Temporal and spatial characterization of a thermogenic, fault-controlled gas hydrate system, Woolsey Mound, Gulf of Mexico

Woolsey Mound, located at Mississippi Canyon Lease Block 118 (MC118), is the site of the Gulf of Mexico hydrate research consortium’s seafloor observatory, where gas hydrates outcrop at the seafloor. The presence of gas hydrates in the mound is confirmed directly by coring and indirectly by 3D seismic reflection data. Craters, pockmarks, chemosynthetic communities, and authigenic carbonates populate the seafloor at Woolsey Mound. Each crater is characterized by a network of shallow crestal faults that connect the hydrate mound to the underlying allochthonous salt body. We characterize the temporal and spatial evolution of gas hydrates at Woolsey Mound under natural perturbations using four collocated 3D seismic reflection data sets that span over 14 years. Data acquisition differences embedded in the data sets arising from variation in geometry, sample rate, and phase are minimized using the “cross-equalization” method. Our results indicate that hydrate formation and dissociation vary temporally and spatially in close connection to the shallow crestal faults. Evidence of gas hydrate dissociation is observed over a period of three years (2000–2003), where major dissociation occurred along the southern portion of the crestal fault in the southeast crater. The dissociation is less prominent in the southwest crater. Evidence of methane venting is observed between 2000 and 2010, which is mostly concentrated in the southeast crater. The residual amplitude anomalies observed between 2000 and 2014 in the mound are mostly positive, implying that the methane venting had increased significantly. The positive anomalies are correlated with the methane seepage recorded in 2011. Our results indicate the evolution of a fault-controlled gas hydrate system in the northern Gulf of Mexico, which would aid in assessing its impact on the seafloor.

Взрывная дегазация Земли на полуострове Ямал и прилегающей акватории Карского моря

Remote sensing data from space and using UAVs make it possible to solve a wide range of tasks related to the study of Earth degassing processes in the Arctic. For the first time, via comprehensive aerospace research on the Yamal Peninsula, we have discovered 4992 zones of gas blowouts (explosions) in the form of craters (pockmarks) at the bottom of 3551 thermokarst lakes and 16 rivers. In addition, we have identified another 669 zones of explosive degassing in the coastal zones of the Kara Sea, mainly in gulfs, estuaries and bays. Taking into account the Yugorsky Peninsula and Bely Island, we have detected 6022 explosive degassing zones in the studying region, including 905 ones offshore. We have proved previously made conclusions that the Neytinsko-Seyakhinsky and Sabetta districts are the most gas-explosive. It is substantiated that possible intense natural degassing of the Earth, especially occurring in the process of degradation of subaquatic permafrost and dissociation of gas hydrates, can radically change the elastic-strength properties of bottom soil, while its saturation with gas can disrupt conditions for the construction of various objects, including underwater gas pipelines. Widespread gas blowouts in the north of Western Siberia with the formation of craters on land and offshore can lead to emergencies and even disasters at oil and gas industrial facilities and to fires in the tundra.

Numerical simulation of the development of hydrate-bearing layers by depressurization of radial wells

A perpendicular bisector unstructured grid was used for meshing a model with radial wells, and the non-orthogonal correction of the flux calculation was implemented in the Tough+Hydrate software. A numerical simulation model was established based on the geological parameters of hydrate-bearing layers (HBLs) in the Shenhu area of the South China Sea. Gas and water production from the HBL, developed through depressurization of radial wells, was studied, and factors influencing gas production were analyzed. The findings indicate that employing radial wells in both hydrate and mixed layers significantly accelerated gas and water production in the HBL, facilitating rapid depressurization. Faster depressurization, in turn, promoted the dissociation of natural gas hydrate (NGH) and increased gas production. Cumulative gas production using radial wells in double layers increased by 110.03% compared with a horizontal well. In the later stage of depressurization development, NGHs in the mixed layer were almost entirely dissociated, whereas nearly three-quarters of NGHs in the hydrate layer remained undissociated. The combined method of depressurization and thermal stimulation is expected to further promote NGH dissociation and enhance gas production. Analysis of influencing factors revealed that higher gas production was associated with a greater number of laterals and larger lateral length, whereas the layout of the laterals had little effect on performance.

Comparison of physicochemical properties between CO2 and CH4 nanobubbles produced by gas hydrate decomposition

Nanobubbles, known for their distinctive physicite and chemical properties, have been successfully applied in various fields. However, the basic properties of nanobubbles formed by gas hydrate dissociation remain poorly understood. In this work, a series of experiments are conducted to investigate the physicochemical properties and stability of CO2 and CH4 nanobubbles produced by hydrate dissociation. The results indicate that the average size of CO2 and CH4 nanobubbles derived from hydrate decomposition slightly increases as the static time prolongs, exhibiting the excellent stability of nanobubbles. Similar to macroscopic bubbles, the size variation of both nanobubble types exhibits a positive correlation with temperature. The absolute value of the surface zeta potential of the CH4 nanobubbles decreases with time, while the opposite is true for the CO2 nanobubbles. Moreover, the expansion in size for both nanobubble types demonstrates a negative correlation with increasing pH, whereas the zeta potential displays a positive correlation with pH. We observed that nanobubble potential is substantially influenced by metal cations within the solution, and the potential effect of CO2 and CH4 nanobubbles was preliminarily discussed by settlement tests as well. These findings may serve as valuable references for future assessments of the role of nanobubbles in reservoir seepage processes and the advancement of gas hydrate technology.

Dissociation of Gas Hydrates in the Combustion Environment

This paper proposes mathematical models of gas hydrate decomposition in high-temperature media. These models are based on heat and mass balances with a set of assumptions about transfer mechanisms and features of chemical reactions. The calculations provide an insight into dynamics of hydrate particles in a flame environment and shed light on possible results of interaction between the combustion front and emission of gas and vapor. Several examples are provided to illustrate the potential of hydrates as a fuel and as a flame extinguishing material. The developed models enable the generation of numerical estimates, which can be employed to design technologies for beneficial uses of gas hydrates.

Permeability of surface clay-bearing sediments in Shenhu Area of South China Sea

The migration of fluids, such as the dissociation of natural gas hydrates, can affect the stability of the seabed and even induce submarine geological disasters and change the marine environment. The migration of fluids in sediments depends on its permeability properties. Therefore, it is crucial to investigate the sediment permeability and its influencing factors. This paper investigates the particle size, porosity, pore size distribution, and permeability of surface clay-bearing sediments in the Shenhu Area of the South China Sea by physical property tests, computed tomography (CT) scanning tests, constant rate of strain (CRS) consolidation tests, and nuclear magnetic resonance (NMR) tests. The permeability of the surface sediments in the Shenhu Area ranges from 3.32 × 10−15–6.76 × 10−14 m2. The pore size mainly ranges between 10−5 and 10−1 mm, exhibiting a bimodal distribution with peaks from 10−4 and 10−2 mm. The increase in clay content leads to enhanced permeability due to the bimodal distribution of pore sizes, which will cause the enlargement of pores. As the pore size increases, the sediment permeability also increases. Sediment permeability linearly decreases with increasing effective axial stress and deformation due to compression of the pore space. Additionally, a new model for calculating permeability with different sediment properties is established, which improves the accuracy of permeability calculations for clay-bearing sediments compared to previous research. The findings of our study can provide a reference for exploring the influence of sediment parameters on fluid migration mechanisms in clay-bearing sediments.

Geomechanical responses of sand–clay interbedded gas hydrate-bearing deposits under depressurization-driven gas production at site UBGH2-6 in Ulleung Basin, offshore Korea

This study explores geomechanical responses of sand-clay interbedded hydrate reservoirs subjected to depressurization. A thermo-hydro-mechanically (T-H-M) coupled simulation code was created to simulate T-H-M interactions in layered hydrate reservoirs, utilizing an explicit two-way coupling scheme. The code was then used to model a hydrate reservoir analogous to a hydrate deposit system in Ulleung Basin, Offshore Korea (Site UBGH2-6). Hydrate reservoirs comprising thin and interbedded sand-clay layers exhibit unique geomechanical responses due to the localized gas hydrate dissociation along sand-clay layer interfaces. The localized dissociation pattern leads to accelerated sediment consolidations along the layer interfaces. The simulation results also reveal development of shear deformation along the sand-clay interfaces, which implies the layer interfaces may act as the main sources of sand productions and fines migration within a depressurized hydrate reservoir. Additional simulations are conducted to further investigate the effects of depressurization rate and formation wettability on gas productivity. Although faster depressurization speeds up initial gas production, ultimately, the production rate is governed by the final bottom hole pressure, regardless of the depressurization rate. Nonetheless, slower depressurization appears more favorable, given its capacity to mitigate initial geomechanical responses, such as reservoir compaction and sand production, thus preserving the long-term production potential of a hydrate reservoir. On the other hand, a cyclic depressurization scheme also proves to be able to mitigate the level of initial geomechanical responses, but only at the cost of reduced gas productivity. A comparative analysis with varying wettability indicates that water-wet reservoirs may be more favorable target for gas hydrate exploitation than gas-wet reservoirs. The presented results enhance understanding of complex hydrate reservoir dynamics and contribute to advancement of sustainable and efficient hydrate production techniques.