Hydrate Formation In Sediments Research Articles

Kinetic study of fulvic acid on methane hydrate formation and decomposition in clay-rich silty sediments

Humic substances and salts are widely distributed in marine sediments, a phenomenon that undoubtedly increases the complexity of recovering methane from hydrate. In this work, kinetic experiments were carried out to determine the role of fulvic acid (FA) on methane hydrate formation and decomposition in marine sediments. We used the mixed clay-rich silty with pore water, containing 3.0 wt% NaCl, to simulate the sediments, with experimental pressure (12.7–14.6 MPa) and temperature (8.6–16.2 °C) conditions adopted from the hydrate reservoir of Shenhu area, South China Sea (SHCS). Results revealed that FA has favorable/unfavorable effects on methane hydrate formation in the sediments, in a concentration-dependent manner. FA solutions, at concentrations of 6.0 and 10.0 wt%, inhibited the formation of methane hydrate, because the high-water holding capacity itself could reduce water activity. Conversely, 2.0 wt% FA solution accelerated methane hydrate formation by arranging surrounding water molecules with H-bonds. Interestingly, it was found that the addition of FA could significantly weaken NaCl's inhibitory effect on methane hydrate formation, while water conversion ratios increased ∼2/3-fold relative to NaCl without FA solution containing systems. These results suggested that presence of FA in marine sediments promoted hydrate reformation during reservoir production. Besides, we found that there is a synergistic effect between FA and NaCl in the process of methane decomposition.

Geological characterization of natural gas hydrate bearing sediments and their influence on hydrate formation and dissociation

Lithology of host sediments associated with gas hydrate reservoirs have a significant effect on the hydrate formation. The Krishna-Godavari (K-G), Mahanadi and Andaman basin in India have been proven to be rich in natural gas hydrate. In this study, a detailed investigation was carried out for the mineralogical analysis of the sediments collected from K-G, Mahanadi and Andaman basin along with hydrate formation in sediments. The study reveals that, the majority of the minerals in K-G basin samples are clay minerals and quartz. The presence of pyrite crystal (FeS2) in the K-G basin sediment is the indication of anoxic and sulfide environment. Spares fragments of microfossil like diatoms and spicules of fresh-water sponges have been identified from K-G basin sediments. Mahanadi basin is also consisting of clay minerals & quartz, and proportion of clay minerals are higher than K-G basin sediment. Andaman basin is mainly composed of clay and calcite minerals with little amount of quartz and feldspar. The rheological behavior of suspensions of sediments in water was investigated as it has significant effect on the drilling operation through the formation. Considering the similar mineralogical composition, gas hydrate formation and dissociation behavior were investigated in colloidal suspension containing sediments collected from K-G basin. Hydrate formation studies indicated that the presence of sediment solution significantly decreased pressure needed for hydrate formation compared to formation in pure water alone. It was observed that the salinity has delayed the hydrate formation as salt is considered as hydrate inhibitor. The rate of hydrate formation was observed to be high in case of sediment aqueous solution than the pure water. Whereas, in case of sediment solution with salinity shows lower formation rate than both pure water and sediment aqueous solution. The studies are relevant to the origin and stability of natural gas hydrate deposits known to exist in deep permafrost and marine sediments, where the effect of sediment surfaces is largely unknown.

Advances in Characterizing Gas Hydrate Formation in Sediments with NMR Transverse Relaxation Time

The formation process, structure, and distribution of gas hydrate in sediments have become focal points in exploring and exploiting natural gas hydrate. To better understand the dynamic behavior of gas hydrate formation in sediments, transverse relaxation time (T2) of nuclear magnetic resonance (NMR) is widely used to quantitatively characterize the formation process of gas hydrate and the change in pore characteristics of sediments. NMR T2 has been considered as a rapid and non-destructive method to distinguish the phase states of water, gas, and gas hydrate, estimate the saturations of water and gas hydrate, and analyze the kinetics of gas hydrate formation in sediments. NMR T2 is also widely employed to specify the pore structure in sediments in terms of pore size distribution, porosity, and permeability. For the recognition of the advantages and shortage of NMR T2 method, comparisons with other methods as X-ray CT, cryo-SEM, etc., are made regarding the application characteristics including resolution, phase recognition, and scanning time. As a future perspective, combining NMR T2 with other techniques can more effectively characterize the dynamic behavior of gas hydrate formation and pore structure in sediments.

Potential applications of distributed optical fiber sensor in hydrate‐induced sedimentary deformation research

AbstractNatural gas hydrate is regarded as a potential clean energy source. However, hydrate phase transition during gas production leads to significant hydrate‐bearing sedimentary layer deformation, which is one of the main obstacles for safe hydrate exploitation. In this study, distributed optical fiber sensors were used to examine the porous medium deformation induced by phase change and verify its feasibility for application in hydrate research. Experiments on ice formation in a porous medium were conducted to mimic the hydrate formation in sediments. Optical fiber sensors were used to record and analyze the strain characteristics caused by the deformation of porous medium during the phase change process. The frequency shift during the cooling process shows that the fiber segment sensitivity is influenced by its initial length and tightness. In experiments with porous medium, the strain caused by the phase change exhibited a linear trend. In a comparative experiment using pure water, the strain caused by the phase change showed a nonlinear trend. The results indicate that the porous medium deformation induced by phase change can be accurately evaluated using strain data from distributed optical fiber sensors. The strain results also reflect the rate of the phase change. This study proves that the distributed optical fiber sensor has the potential to clarify the deformation characteristics of porous medium caused by hydrate phase change.

AE monitoring-based CO2 hydrate formation and its influences to hydrate-bearing sandy sediments

An acoustic emission (AE) monitoring-based CO2 hydrate formation test and the subsequent triaxial compression on hydrate-bearing sandy sediments were performed and the results were discussed. It was found that the formation of CO2 hydrate in sediments can cause an obvious acoustic emission. The hit counts during hydrate formation in sediments grows up over tenfold with an increase of over 55% in the averaged AE energy. All the measured values of AE parameters increases as the continuation of formation, and they are smaller in CO2 injection than that in triaxial compression. Further, AE amplitude corresponding to the maximum hit counts tends to increase due to the formation of CO2 hydrate and the friction in pure sediments. AE characteristics associated with the hydrate formation and triaxial compression on hydrate-bearing sediments contribute to develop a monitoring approach on hydrate dynamics within sediments.

Modelling Methane Hydrate Saturation in Pores: Capillary Inhibition Effects

Experimental and field observations evidence the effects of capillarity in narrow pores on inhibiting the thermodynamic stability of gas hydrates and controlling their saturation. Thus, precise estimates of the gas hydrate global inventory require models that accurately describe gas hydrate stability in sediments. Here, an equilibrium model for hydrate formation in sediments that accounts for capillary inhibition effects is developed and validated against experimental data. Analogous to water freezing in pores, the model assumes that hydrate formation is controlled by the sediment pore size distribution and the balance of capillary forces at the hydrate–liquid interface. To build the formulation, we first derive the Clausius–Clapeyron equation for the thermodynamic equilibrium of methane and water chemical potentials. Then, this equation is combined with the van Genuchten’s capillary pressure to relate the thermodynamic properties of the system to the sediment pore size distribution and hydrate saturation. The model examines the influence of the sediment pore size distribution on hydrate saturation through the simulation of hydrate formation in sand, silt, and clays, under equilibrium conditions and without mass transfer limitations. The results show that at pressure–temperature conditions typically found in the seabed, capillary effects in very fine-grained clays can limit the maximum hydrate saturation below 20% of the host sediment porosity.

Mineralogical and structural characterization of the sediments of Krishna Godavari and Mahanadi Basin and their influences on hydrate formation kinetics

Structural and mineralogical characterization of sediment samples of Krishna Godavari (KG) and Mahanadi (MH) basin was performed with the aim of providing in-depth analysis of the effect of mineralogy, grain size and other properties on the hydrate formation. Bulk mineralogy and clay mineralogy of the sediments analyzed through different characterization techniques like X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) that was associated with Energy Dispersive X-Ray (EDX) analysis. Quartz was the main component observed in the sediment samples. A relation between particle size and pore size was also established through particle size (DLS) and pore size characterization (BET) techniques. Finer clay materials were leading in both KG and MH basin samples having slight variation in their quartz content. Illite and smectite were the dominating clay minerals found in the sediments with calcite and albite being the other contributing minerals. Framboids as the pyrites were also observed in sediments and were clearly visible in FESEM observations. Hydrate formation studies were also performed in the sediments to observe the effect of their sedimentology and geology on the occurrence of hydrates in oceanic sediments. Hydrate formation in sediments occurred in less time as compared to pure water system with an accelerated rate of nucleation as per the observations. Kinetic studies were also performed that showed the higher initial rate of hydrate formation in sediments that could be due to the high surface area and additional nucleation sites provided by the sediments as confirmed by BET analysis. Rate constants and other kinetic parameters were also calculated by assuming the first order reaction kinetics of hydrate formation.

One-Dimensional Study on Hydrate Formation from Migrating Dissolved Gas in Sandy Sediments

Upward migration of gas-dissolved pore fluid is an important mechanism for many naturally occurring hydrate reservoirs. However, there is limited understanding in this scenario of hydrate formation in sediments. In this preliminary work, hydrate formation and accumulation from dissolved gas in sandy sediments along the migration direction of brine was investigated using a visual hydrate simulator. Visual observation was employed to capture the morphology of hydrates in pores through three sapphire tubes. Meanwhile, the resistivity evolution of sediments was detected to characterize hydrate distribution in sediments. It was observed that hydrates initially formed as a thin film or dispersed crystals and then became a turbid colloidal solution. With hydrate growth, the colloidal solution converted to massive solid hydrates. Electrical resistivity experienced a three-stage evolution process corresponding to the three observed hydrate morphologies. The results of resistivity analysis also indicated that the bottom–up direction of hydrate growth was consistent with the flow direction of brine, and two hydrate accumulation centers successively appeared in the sediments. Hydrates preferentially formed and accumulated in certain depths of the sediments, resulting in heterogeneous hydrate distribution. Even under low saturation, the occurrence of heterogeneous hydrates led to the sharp reduction of sediment permeability.

Stages in the Dynamics of Hydrate Formation and Consequences for Design of Experiments for Hydrate Formation in Sediments

Natural gas hydrates in sediments can never reach thermodynamic equilibrium. Every section of any hydrate-filled reservoir is unique and resides in a stationary balance that depends on many factors. Fluxes of hydrocarbons from below support formation of new hydrate, and inflow of water through fracture systems leads to hydrate dissociation. Mineral/fluid/hydrate interaction and geochemistry are some of the many other factors that determine local hydrate saturation in the pores. Even when using real sediments from coring it is impossible to reproduce in the laboratory a natural gas hydrate reservoir which has developed over geological time-scales. In this work we discuss the various stages of hydrate formation, with a focus on dynamic rate limiting processes which can lead to trapped pockets of gas and trapped liquid water inside hydrate. Heterogeneous hydrate nucleation on the interface between liquid water and the phase containing the hydrate former rapidly leads to mass transport limiting films of hydrate. These hydrate films can delay the onset of massive, and visible, hydrate growth by several hours. Heat transport in systems of liquid water and hydrate is orders of magnitude faster than mass transport. We demonstrate that a simple mass transport model is able to predict induction times for selective available experimental data for CO2 hydrate formation and CH4 hydrate formation. Another route to hydrate nucleation is towards mineral surfaces. CH4 cannot adsorb directly but can get trapped in water structures as a secondary adsorption. H2S has a significant dipole moment and can adsorb directly on mineral surfaces. The quadropole-moment in CO2 also plays a significant role in adsorption on minerals. Hydrate that nucleates toward minerals cannot stick to the mineral surfaces so the role of these nucleation sites is to produce hydrate cores for further growth elsewhere in the system. Various ways to overcome these obstacles and create realistic hydrate saturation in laboratory sediment are also discussed.

N2O hydrate formation in porous media: A potential method to mitigate N2O emissions

Increasing nitrous oxide (N2O) emissions and their potential impacts on the ozone layer are of worldwide concern. Hydrate-based sequestration technology is considered to be a promising method for N2O control. This study investigated the conditions required for N2O sequestration through forming hydrates. Magnetic resonance imagining (MRI) was used to capture and quantify N2O hydrate formation in porous media simulated by fine quartz sands. The effect of the sequestration conditions on hydrate formation were investigated, involving pressure (1.5, 2, and 2.5 MPa), temperature (275.15, 276.15, and 277.15 K) and initial water saturation (25.06, 33.23, 42.13, and 50.81%). The results indicated the inhomogeneous formation and distribution of N2O hydrates in pore spaces. Initial water saturation and pressure were found to significantly impact the hydrate distribution during the initial formation stage. Moreover, N2O hydrates formed more rapidly in sediments with a lower water saturation and temperature, indicating that sufficient contact between gas and water and a higher driving force are crucial for abundant hydrate formation. A higher initial water saturation could help improve the sequestration efficiency, which would play a crucial role in locating the sequestration site. This work could provide some insights of the mechanism of N2O sequestration via hydrate formation in sediments, making contributions to potential applications in field tests.

Simulating natural hydrate formation and accumulation in sediments from dissolved methane using a large three-dimensional simulator

The slow hydrate formation and accumulation process from dissolved gas in nature was simulated at large-scale in sandy sediments using a three-dimensional hydrate simulator. A low hydrate formation rate (0.37% pore volume per day) was achieved by maintaining the supersaturation of dissolved methane and migration velocity of the pore fluid at very low levels. Electrical and acoustic measurements were performed to track the hydrate formation in the sediments. A dynamic hydrate evolution process was observed: Crystallization – migration – accumulation – recrystallization. This evolution process has a critical effect on the connectivity of the pores and the strength of the sediment frame. After the dynamic evolution process, stiff frame-supporting hydrates and patchy hydrates were observed as the final morphologies in the pores, although the variation in the acoustic velocity indicated that frame supporting was the dominating morphology in the pores. Based on this, hydrate saturation values were inversed from resistivity and acoustic velocity models for frame-supporting hydrates. The calculated results showed that the order of hydrate saturation at different sites from the resistivity model was consistent with that from the acoustic velocity model by overestimating the hydrate saturation obtained from the resistivity inversion. Analysis of the spatial hydrate distribution showed that hydrate distribution in the sediments was discontinuous. The concentration, temperature, and fluid velocity profiles play a key role on this discontinuity, which we propose should be considered in detail in future experimental and numerical studies.

The elastic wave velocity response of methane gas hydrate formation in vertical gas migration systems

Knowledge of the elastic wave velocities of hydrate-bearing sediments is important for geophysical exploration and resource evaluation. Methane gas migration processes play an important role in geological hydrate accumulation systems, whether on the seafloor or in terrestrial permafrost regions, and their impact on elastic wave velocities in sediments needs further study. Hence, a high-pressure laboratory apparatus was developed to simulate natural continuous vertical migration of methane gas through sediments. Hydrate saturation (Sh) and ultrasonic P- and S-wave velocities (Vp and Vs) were measured synchronously by time domain reflectometry (TDR) and by ultrasonic transmission methods respectively during gas hydrate formation in sediments. The results were compared to previously published laboratory data obtained in a static closed system. This indicated that the velocities of hydrate-bearing sediments in vertical gas migration systems are slightly lower than those in closed systems during hydrate formation. While velocities increase at a constant rate with hydrate saturation in the closed system, P-wave velocities show a fast–slow–fast variation with increasing hydrate saturation in the vertical gas migration system. The observed velocities are well described by an effective-medium velocity model, from which changing hydrate morphology was inferred to cause the fast–slow–fast velocity response in the gas migration system. Hydrate forms firstly at the grain contacts as cement, then grows within the pore space (floating), then finally grows into contact with the pore walls again. We conclude that hydrate morphology is the key factor that influences the elastic wave velocity response of methane gas hydrate formation in vertical gas migration systems.

Hydrate formation in sediments from free gas using a one-dimensional visual simulator

To study natural gas hydrate formation in sediments, a one-dimensional visual hydrate simulator with three visual sapphire tubes and twelve electrode tips was designed and constructed. Using this device, the hydrate formation process was experimentally studied in coarse sands, silts, and natural clay marine sediments from free methane gas. During experiments, each of which lasting up to three weeks, a hydrate film formed initially at the gas-water interface and spread out to form a film network in sediments. The hydrate film grew in thickness by adsorbing water, where film thickening and water adsorption occur intermittently. The salting-out effect and the osmosis effect play a critical role in the hydrate film thickening-water adsorption process, and the perturbation arising from the fluctuation such as fluid flow and temperature may accelerate the hydrate formation. A colloidal solution formed from hydrate and salt water was also observed, which may be a new form of existence for marine natural gas hydrate. Electrical resistivity of the sediments initially decreased as hydrate formation increased the remaining water salinity, and then increased when additional hydrate formation restricted the water distribution in the sediment. Among three studied sediments, massive hydrate deposits were observed in coarse sand and silt but not in clay marine sediment, while fractures appeared when massive hydrates formed in sediments.

Experimental Investigation into Gas Hydrate Formation in Sediments with Cooling Method in Three-Dimensional Simulator

Gas hydrate formation behaviors in sediments were investigated in a three-dimensional reactor using the cooling method. The characteristics of the temperature change, the heat transfer, the gas consumption, and the electrical resistance change in the hydrate formation process were studied. The results show that the temperature in the reactor gradually decreases from the near-wall to the center in the cooling process. The gas hydrate preferentially forms in the inner-wall regions of the reactor, which has a low temperature in the cooling process, and then the formation spreads to the surrounding area. On the basis of the balance of energy, it was found that the temperature change was roughly equal to the values calculated in the early stage of the hydrate formation. At the beginning of the hydrate formation, the hydrate formation rates at different places are very different from each other. The gas consumption rate first rises and then falls as the supercooling degree increases during the whole process. The changes of the temperature and resistance illustrate that the methane hydrate inhomogeneously distributes in the reactor.

Acoustic response of gas hydrate formation in sediments from South China Sea

Gas hydrate has been recognized as a potential energy resource in South China Sea (SCS). Understanding the acoustic response of gas hydrate formation in the SCS sediments is essential for regional gas hydrate investigation and quantification. The sediments were obtained from gravity core sampling at E 115°12.52363′ N 19°48.40299′. Gas hydrate was formed within a “gas + water-saturated SCS sediments” system. Combination of a new bender element technique and coated time domain reflectometry (TDR) was carried out to study the acoustic response of hydrate occurrence in SCS sediments. The results show the acoustic signal becomes weak when hydrate saturation (Sh) is lower than 14%. The acoustic velocities (Vp, Vs) of the sediments increase with Sh during hydrate formation, and Vs increases relatively faster when Sh is higher than 14%. These results indicate that tiny hydrate particles may firstly float in the pore fluid, which causes a significant acoustic attenuation, but has little influence on shear modulus. As time lapses and Sh approaches 14%, numerous particles coalesce together and contact with sediment particles. As a result, Vs has a sharp increase when hydrate saturation exceeds 14%. Several velocity models were validated with the experimental data, which suggests a combination of the BGTL (Biot–Gassmann Theory modified by Lee) model and the Weighted Equation is suitable to estimate Sh in SCS.

Experimental Studies on the Evolvement of Electrical Resistivity during Methane Hydrate Formation in Sediments

An experimental setup was developed to in situ measure the evolvement of the electrical resistivity during hydrate formation process to aid the interpretation of the influence of hydrate saturation...

Particle size effect on the saturation of methane hydrate in sediments – Constrained from experimental results

Except for those occurring at seafloor, most of natural gas hydrate form in sediments and are subject to the influence of sediment. Among these factors, the particle size effect on hydrate saturation level in sediment have been studied with a series of silica sands with various sizes, and the results obtained clearly indicate that particle size does play an important role in affecting the saturation level of hydrate in sediments. The proton relaxation times of water confined in the same series of silica sands, which were determined with NMR measurement, show logarithmic relationship with particle size. By comprehensive consideration of the results of hydrate saturation and water proton relaxation times, the particle size effect observed is tentatively explained by the water availability for hydrate formation in sediments.

Evolution of Compressional Wave Velocity during CO2Hydrate Formation in Sediments

While the acoustic wave-based survey is considered to be one of the most effective and promising means for monitoring the behavior of particulate/discrete geomaterials, the P-wave velocity has scarcely been used to monitor the long-term behavior of CO2 sequestered sediments or to understand the characteristics of CO2 hydrate formation in sediments. Furthermore, there are still only limited reliable laboratory results quantifying the P-wave velocity change in sediments that results from CO2 hydrate formation and accumulation processes. This study presents experimental measurements on the evolution of P-wave velocity as CO2 hydrate saturation increases in unconsolidated sediment. The measured data are compared with the simple yet robust asymptotic Gassmann model to estimate CO2 hydrate saturation (volume fraction of hydrate in pore space) in sediments. Given that in situ techniques to measure acoustic waves are well-established for the exploration of deep oceanic sediment, the methodology presented in this ...

97/01185 Hydrate formation in sediments in the sub-seabed disposal of CO 2

Two Zn-based sorbents, named as L-991 and L-992, used for hot gas desulfurization were developed. The L-992, which was prepared by changing Zn/Ti ratio and adding certain proportion of Cu and Mn metal oxide, has better performance than L-991. The suitable desulfurization temperature was 600–700 °C for the L-991 and 600–800 °C for the L-992. The sulfur capacity was about 16 g/100 g and 19–21 g/100 g of L-991 and L-992 respectively. After 17 multi-cycles sulfidation/regeneration tests, the sulfur capacity of the L-991 decreased greatly, while that of the L-992 still remained at 17 g/100 g. Both the sorbents showed orderly crystalline orientation and the particle size did not change. Sulfidation and regeneration tests were done both on lab micro-fixed-bed reactor and SMOVEN equipment. During the continuous tests, the H2S concentration can be reduced from about 10 g/m3 to less than 20 mg/m3, the H2S removal efficiency was > 99%.

Hydrate formation in sediments in the sub-seabed disposal of CO 2

Sub-seabed disposal is the safest disposal option for CO 2. Water pressure and dilution into oceanic water prevent direct emission of CO 2 into the air. Sediments under the deep sea floor are usually cool because the deep oceanic water is very cool. CO 2 hydrate forms in the sediments in areas of the sea floor deeper than 300 m. The formation of CO 2 hydrate in sediment pores almost completely prevents the escape of CO 2.