Layered Hydrate Research Articles

Tautomeric pillars in vanadyl phosphate cathode to screen the divalent charge on Zn2+ for aqueous Zn batteries

Cathode materials with high redox potential are important for constructing high-energy-density aqueous zinc batteries. The polyanion compound of layered hydrate vanadyl phosphate (H2O-VOP) provides high potential thanks to the inductive effect. However, the sluggish Zn2+ diffusion in the lattice results in large voltage hysteresis, obstructing the capacity release at high voltage. Herein, tautomeric pillars are inserted in the VOPO4 layers (Tau-VOP) by the desulfhydryl reaction of l-cysteine, aiming to suppress voltage hysteresis with their charge screening effect. Specifically, the Lewis alkaline sites on the tautomers capture inserted Zn2+, and the divalent charge is further delocalized over the conjugated structure of pillars. This reduction of effective charge on cations ensures much weakened electrostatic interactions with the lattice and reduced diffusion barrier. As a result, the Tau-VOP cathode achieves 193 mAh g−1 capacity with 1.47 V/1.6 V redox voltage in zinc cells, which are superior to 110 mAh g−1 capacity and 1.1 V average discharge voltage with large voltage hysteresis obtained with H2O-VOP. The rate performance and energy efficiency are also significantly improved with the help of tautomer pillars. This work presents an effective charge screening strategy by suitable pillars to facilitate multivalent cation transport in cathode structures and enhance electrochemical performance.

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.

Understanding the Super-Theoretical Capacity Behavior of VO2 in Aqueous Zn Batteries.

VO2 material, as a promising intercalation host, is widely investigated not only in aqueous lithium-ion batteries, but also in aqueous zinc-ion batteries (AZIBs) owing to its stable tunnel-like framework and multivalence of vanadium. Different from lithium-ion storage, VO2 can provide higher capacity when storing zinc ions, even exceeding its theoretical capacity (323mAhg-1), but the specific reason for this unconventional performance in AZIBs is still unclear. The present study proposes a catalytic oxygen evolution reaction (OER) coupled with an interface oxidation mechanism of VO2 during the initial charging to a high voltage. This coupling induces a phase transformation of VO2 into a high oxidation state of V5O12∙6H2O, enabling a nearly two-electron reaction and providing additional zinc storage sites to achieve super-theoretical capacity. Furthermore, it is demonstrated that these vanadium oxide cathodes (V2O3, VO2, and V2O5) will all undergo phase change after the first charge or short cycle. Notably, water molecules participate in the final formation of layered vanadium-based hydrate, highlighting their crucial role as "pillars" for stabilizing the structure. This work significantly enhances the understanding of vanadium-based oxide cathodes.

Enhanced UV Light‐Emission of Zinc‐Phosphate‐Hydrate Hydrothermally‐Grown on Cu Metal Substrates for Opto‐Electronic Applications

AbstractIn the present study, polycrystalline films of layered zinc phosphate hydrate are produced by a facile, low‐temperature single‐step hydrothermal fabrication method on top of Cu metal substrates. Despite containing structural water, the as‐grown films remain crystalline, chemically stable, and electrically conductive. The photoluminescence spectrum obtained at room‐temperature reveals the presence of a spectrally narrow, high‐intensity ultraviolet band that consists of two Gaussian peaks at ≈377 and 383 nm and a UV‐to‐visible peak emission intensity ratio of ≈5.3. The electrical charge‐transport properties remain Ohmic for electric fields of up to ≈2 kV m−1 and temperature (T) range of ≈223–368 K. The electrical conductivity is further found to vary exponentially with the inverse temperature, and the thermal activation energy, Ea is 285 ± 8 meV. A moderate UV‐vis photoconduction effect is registered and assigned to light‐assisted electronic transitions that involve near‐band edge defect states. This study can potentially open a door to the engineering and deployment of water‐based compounds with advanced, semiconducting‐like attributes in short‐wavelength opto‐electronic devices.

Numerical simulations of the synthetic processes and consequences of secondary hydrates during depressurization of a horizontal well in the hydrates production

The depressurization method was implemented through a horizontal well in the production test at Shenhu, the South China Sea in 2020. The numerical model of a layered hydrate reservoir was established based on the in-field data of this test. The gas production rates measured was validated by comparing with the numerical results. The synthesis time, scopes, gas sources and maximum saturations of secondary hydrates were originally clarified by analyzing the data from different monitoring sections, which followed by the sensitivity analyses against the initial permeability of each hydrate-bearing layer. The effect of secondary hydrates on the short-term and long-term productions was quantified. The hydrates were resynthesized extensively above the interface between the natural gas hydrate layer and the mixing layer, which reduced the in-situ permeability and then the well gas production seriously. The areas affected by depressurization were constrained within the mixing layer. The gas sources were supplemented by the primary free gas and the gas decomposed by the hydrates in the upper mixing layer. The vertical extensions of the secondary hydrates were limited to about 5 m due to the lower permeability, while the horizontal distributions were approximately 78 m away from the horizontal well after 3 years. Given that the secondary hydrates were eliminated artificially, the cumulative gas volume produced in the horizontal well was increased by 24% after 3 years. The sensitivity analysis showed that the variations of permeability in the mixing layer had more obvious effects on secondary hydrates. Therefore, the hydraulic fracturing could be used to prevent the resynthesis of hydrates.

Theoretical Studies of Nonlinear Relaxation Electrophysical Phenomena in Dielectrics with Ionic–Molecular Chemical Bonds in a Wide Range of Fields and Temperatures

This paper is devoted to the development of generalized (for a wide range of fields (100 kV/m–1000 MV/m) and temperatures (0–1500 K) in the radio frequency range (1 kHz–500 MHz)) methods for the theoretical investigation of the physical mechanism of nonlinear kinetic phenomena during the establishment of the relaxation polarization, due to the diffusion motion of the main charge carriers in dielectrics with ionic–molecular chemical bonds (hydrogen-bonded crystals (HBC), including layered silicates, crystalline hydrates and corundum–zirconium ceramics (CZC), etc.) in an electric field. The influence of the nonlinearities equations of the initial phenomenological model of dielectric relaxation (in HBC-proton relaxation) on the mechanism for the formation of volume–charge polarization in solid dielectrics is analyzed. The solutions for the nonlinear kinetic Fokker–Planck equation, together with the Poisson equation, for the model of blocked electrodes are built in an infinite approximation (including all orders k of smallness without dimensional parameters) of perturbation theory for an arbitrary order r of the frequency harmonic of an alternating external polarizing field. It has been established that the polarization nonlinearities in ion-molecular dielectrics, already detected at the fundamental frequency, are interpreted in the mathematical model (for the first time in this work) as interactions of the relaxation modes of the volume charge density calculated on different orders of spatial Fourier harmonics. At the fundamental frequency of the field, an analytical generalized expression is written for complex dielectric permittivity (CDP), which is expressed analytically in terms of special relaxation parameters, which are quite complex real functions in the fields of frequency and temperature. The theoretical CDP and the dielectric loss tangent spectra studied depend on the nature of the relaxation processes in the selected temperature range (Maxwell and diffusion relaxation; thermally activated and tunneling relaxation), which is relevant from the point of view of choosing exact calculation formulas when analyzing the optimal operating modes of functional elements (based on dielectrics and their composites) for circuits of instrumentation, radio engineering and power equipment in real industrial production.

Experimental Investigation into Three-Dimensional Spatial Distribution of the Fracture-Filling Hydrate by Electrical Property of Hydrate-Bearing Sediments

As a future clean energy resource, the exploration and exploitation of natural gas hydrate are favorable for solving the energy crisis and improving environmental pollution. Detecting the spatial distribution of natural gas hydrate in the reservoir is of great importance in natural gas hydrate exploration and exploitation. Fracture-filling hydrate, one of the most common types of gas hydrate, usually appears as a massive or layered accumulation below the seafloor. This paper aims to detect the spatial distribution variation of fracture-filling hydrate in sediments using the electrical property in the laboratory. Massive hydrate and layered hydrate are formed in the electrical resistivity tomography device with a cylindrical array. Based on the electrical resistivity tomography data during the hydrate formation process, the three-dimensional resistivity images of the massive hydrate and layered hydrate are established by using finite element forward, Gauss–Newton inversion, and inverse distance weighted interpolation. Massive hydrate is easier to identify than layered hydrate because of the big difference between the massive hydrate area and surrounding sediments. The diffusion of salt ions in sediments makes the boundary of massive hydrate and layered hydrate change with hydrate formation. The average resistivity values of massive hydrate (50 Ω⋅m) and layered hydrate (1.4 Ω⋅m) differ by an order of magnitude due to the difference in the morphology of the fracture. Compared with the theoretical resistivity, it is found that the resistivity change of layered hydrate is in accordance with the change tendency of the theoretical value. The formation characteristic of massive hydrate is mainly affected by the pore water distribution and pore microstructure of hydrate. The hydrate formation does not necessarily cause the increase in resistivity, but the increase of resistivity must be due to the formation of hydrate. The decrease of resistivity in fine-grains is not obvious due to the cation adsorption of clay particles. These results provide a feasible approach to characterizing the resistivity and growth characteristics of fracture-filling hydrate reservoirs and provide support for the in-situ visual detection of fracture-filling hydrate.

The features of the crystal structure of the layered series hydrates of uridine-5'-monophosphate salts (UMPNa x ·yH2O).

Almost all reported salts of nucleotides crystallized from solutions are in the form of hydrate. Layered hydrates often occur in crystals with more than five water molecules per host molecule. In the present report, five single-crystal structures of uridine-5′-monophosphate (UMP) series hydrates of acid or salts (UMPNax·yH2O, x = 0–2) were determined and analysed. It was found that all crystal hydrates were orthorhombic with a C2221 space group but with mere variation in the plane angle of adjacent bases and the distance between phosphate arms. The packing arrangements of UMPNax·yH2O hydrates present typical layered sandwich structures and show that the UMP molecular layers alternate with water molecular layers parallel to the ac plane, linked by hydrogen bonds or coupled with coordinate bonds besides ionic electrostatic interaction. Metal ions were located in water molecular layers as a form of hydration. In addition, we tried to deduce and give insights into the formation of UMPNax·yH2O hydrates. The effect of water molecules and metal ions on the crystal structure and stability was investigated. It was found that the coexistence of relatively rigid architectures constructed by host molecules and flexible interlayer regions was a key factor to the formation of these hydrates. Excessive loss of lattice water would give rise to the irreversible collapse of the host structure and loss of ability to recover to the initial state under humidity. Approximately seven crystal-water molecules were the balance point of sodium salt hydrates at room temperature under 43–76% RH conditions. The number of sodium ions in the crystal lattice is positively correlated with their thermal stability.

Multiple porosity model of a heterogeneous layered gas hydrate deposit in Ulleung Basin, East Sea, Korea: A study on depressurization strategies, reservoir geomechanical response, and wellbore stability

Precise simulation of the geomechanical response is crucial for the gas hydrate production such as from the deposits in Ulleung Basin, East Sea, Korea, which exhibit severe vertical heterogeneity of the hydrate-bearing sand and mud layers. Physically, depressurization causing hydrate dissociation can induce critical subsidence. Meanwhile, it is numerically cumbersome to apply the fine-scale single porosity model to the heterogeneous layered system particularly for geomechanics. In this study, to investigate geomechanical responses of the intercalated layer system based on various depressurization scenarios, we employ a multiple porosity (MP) model with upscaled geomechanical properties while flow variables kept in the fine-scale. For the rigorous two-way coupling between the fluid flow and geomechanics, the fixed-stress sequential method is employed with two individual simulators, the TOUGH+HYDRATE for the flow and an in-house code (called the ROCMECH) for the geomechanics. Specifically for the ROCMECH, we applied axisymmetric geomechanics for more precise calculation of deformation near the wellbore. Numerical experiments of field-wide simulations are about two different comparison studies for depressurization: a constant bottom hole pressure (BHP) and several different BHPs cases. For a constant BHP case, gas production periods, i.e., 14- and 100-days productions representing short- and long-term, respectively, are compared, while several different BHPs case including continuous and periodic depressurizations is focused on the comparison of the productivity and geomechanical stability. From the case of constant BHP, we confirm significant vertical displacement due to the weaker stiffness of the formation after hydrate dissociation, which can aggravate as the production continues. Among the cases with varying BHP, the periodic depressurization scenario exhibits superiority with significantly small subsidence despite similar productivity. The MP model employed in this study can help devise depressurization strategies for gas hydrate reservoirs, especially for the precise and efficient calculation of the geomechanical responses of the intercalated layer system.

Layered Niobium Oxide Hydrate Anode with Excellent Performance for Lithium-Ion Batteries.

Benefiting from the advantages of cost-effectiveness and sustainability, lithium-ion batteries (LIBs) are recognized as a next-generation energy technology with great development potential. Herein, niobium oxide hydrate (H3ONb3O8) synthesized by a facile and inexpensive solvothermal method is proposed as the anode of LIBs. It is a layered two-dimensional material composed of negatively charged two-dimensional lamellae and positively charged interlayer hydronium ions. The former consist of NbO6 octahedral units connected by bridging oxygen. Because of the mutual effect of hydronium ions and niobium oxide quantum dots, niobium oxide hydrate exhibits excellent electrochemical activity when used as an anode material. This compound is first applied to lithium-ion batteries, obtaining a high specific capacity (1232 mAh g-1) at 100 mA g-1 and maintaining an outstanding performance after 200 cycles. Therefore, this work not only proposes a simple preparation method of niobium oxide hydrate but also expands the variety of high-performance anode materials.

Numerical simulation on gas production from inclined layered methane hydrate reservoirs in the Nankai Trough: A case study

Natural gas hydrate is generally disseminated in tilted sediments. The inclination of hydrate reservoirs significantly affects the fluid migration behaviour and production potential. However, most of the current simulations ideally assume that the hydrate reservoir is horizontally distributed; resulting in the effect of the formation dip on the well deployment and corresponding gas production remains unclear. Here, we implement a real inclined alternating sand–clay hydrate reservoir model based on geological data from the Nankai Trough, Japan, to simulate the production performance of a single horizontal well and dual horizontal wells. Results show that the gas and water productions are enhanced when a single horizontal production well is deployed in the structural low of the reservoir. The gas and water production performance in upper sandy reservoir and the water extraction in the middle muddy reservoir are sensitive to the layout of the production wells, which can cause the daily difference is over 6%. The gas-to-water ratio is independent from the structural deployment positions of the horizontal wells in the same inclined layer. Compared to the single depressurization method, placing a horizontal thermal injection well in the structural high of the upper inclined sandy reservoir and a horizontal production well in the structural low of the same formation improves the gas recovery efficiency nearly twice, which is recommended for production enhancement. Our findings are useful for achieving effective and economic gas recovery from natural inclined layered hydrate reservoirs.

Understanding the electrochemical properties and phase transformations of layered VOPO4⋅H2O as a potassium-ion battery cathode

Layered oxovanadium phosphate hydrate (VOPO4·xH2O) is considered to be a promising cathode material for potassium-ion batteries. However, its correlation between electrochemical properties and structural changes during electrochemical processes still need further exploration. Herein, monohydrate VOPO4·H2O is used as an alkali ion (Li+, Na+, K+) host material that gives superior electrochemical performances in potassium-ion batteries. It has a high discharge capacity of 90 mA h g−1 with a high average potential of 3.5 V and a lifespan of over 650 cycles with 61% retention at 1C rate. Three phase transitions during the potassiation/depotassiation process are observed: KxVOPO4 (0 < x < 0.12, d = 7.06 Å) → αI-KxVOPO4 (0.12 < x < 0.48, d = 6.73 Å) → αII-KxVOPO4 (0.30 < x < 0.55, d = 6.55 Å). The small structural change (≤6% on the c-axis) and the full reversibility of the structural transformation ensure the stable cycling; the large interlayer distance allows a fast K-ion diffusion (10−9–10−11 cm2 s−1). This study provides a comprehensive understanding on electrochemical performances and structural evolutions of VOPO4·H2O. Meanwhile, the small volume variation, high operating potential, and excellent cycling stability of VOPO4·H2O can attract more attention to develop other layered materials beyond transition metal oxides.

Transition Metal Cations Stabilized Layered Vanadate Cathodes for Zinc-Ion Batteries

A general strategy is explored to design and synthesize a series of layered vanadate hydrates. Structural analysis found a small amount of cations entered into the VO layers to form a chemical bonding and lock the layer slabs with a stable structure. The stabilized vanadate hydrates have the expanded layer spacing and the robust layered structures that provide a fast ion migration channel and stand the volume change in the intercalation/de-intercalation of Zinc-ion during the electrochemical reaction, rendering an excellent rate capability and stable cycling performance. Specifically, Mn-stabilized vanadium pentoxide hydrate delivers a specific capacity of 400 mAh/g at a current density of 50 mA/g and 260 mAh/g at 4 A/g with capacity retention of 92% over 2,000 cycles. Several transition metal cations can also play the same role in enhancing Zn-ion storage in layered vanadate hydrates, suggesting a general strategy for exploiting the high-performances cathodes for multi-valent ion batteries.

Formation of a uranyl hydroxide hydrate via hydration of [(UO2F2)(H2O)]7·4H2O.

Hydrated uranyl fluoride, [(UO2F2)(H2O)]7·4H2O, is not stable at elevated water vapor pressure, undergoing a complete loss of fluorine to form a uranyl hydroxide hydrate. Powder X-ray diffraction data of the resultant uranyl hydroxide species is presented for the first time, along with Raman and infrared (IR) spectra. The new uranyl hydroxide species is structurally similar to the layered uranyl hydroxide hydrate minerals schoepite and metaschoepite, but has a significantly expanded interlayer spacing (c = 15.12 vs. 14.73 Å), suggesting that additional H2O molecules may be present between the uranyl layers. Comparison of the Raman and IR spectra of this new uranyl hydroxide hydrate and synthetic metaschoepite ([(UO2)4O(OH)6]·5H2O) suggests that the equatorial environment of the uranyl ion may differ and that H2O molecules in the new species participate in stronger hydrogen bonds. In addition, the interlayer spacing of both this new uranyl hydroxide species and synthetic metaschoepite is shown to be sensitive to the environmental humidity, contracting and re-expanding with desiccation and rehydration. Structural distinction between the new uranyl hydroxide species and synthetic metaschoepite is confirmed by a comparison of the thermal behavior; unlike metaschoepite, the new hydrate does not form α-UO2(OH)2 upon dehydration.

Gas hydrate occurrence and distribution controlled by regional geological structure off eastern India: Estimates from logging-while-drilling in Area-B, National Gas Hydrate Program Expedition 02 (NGHP-02)

Abstract The National Gas Hydrate Program Expedition 02 (NGHP-02) was designed to examine gas hydrate occurrences off the eastern margin of the Indian Peninsula. Twelve holes were logged with logging-while-drilling (LWD) tools and nine holes at five sites were cored in Area-B of NGHP-02. Five logging units were defined based on the characteristics in logging data responses. Distinctive Logging Units R1 and R2 characterized by high gamma ray log values and composed of quartz and biotite-rich medium sized sand grain units that act as gas hydrate resevoirs and correlated to strong seismic reflectors. Hydrate-bearing intervals can be identified by resistivity and sonic velocity logs and classified into pore-filling type, fracture-filling type, and a mixture of pore- and fracture-filling types based on borehole image characteristics. Pore-filling type gas hydrate is typically developed in the case where the depths of R1 and/or R2 is close to the seismic inferred bottom simulating reflector (BSR). Fracture-filling type hydrates associated the R1 section occur above the BSR associated with the anticline in Area-B. The occurrence of pore-filling and fracture-filling gas hydrate represent different processes of hydrate formation related to the regional geological structure. The stratigraphic layered pore-filling gas hydrate occurrences are generated along often dipping sand layers, which are also conduits for methane-bearing fluid migrating from below the BSR in many settings. Fracture-filling type gas hydrate is an alternative mechanism for the occurrence of gas hydrate in mudstone-rich sediments above the BSR and found associated with the anticline in Area-B. This structural constraint of the hydrate-bearing fractures in the Area-B anticline suggest that the fracture dominated reservoirs possibly formed by anticlinal flexure, and the upward flow of methane-bearing fluids along porous sedimentary layers and the subsequent formation of pore-filling gas hydrate occurrences account for the range of gas hydrate accumulations discovered during NGHP-02.

Peculiarities of natural gas hydrate formation from ice in reactors under high pressure

Experimental results of natural gas hydrates formation from ice obtained under static conditions in the batch reactor applying the method of thermal cycling have been given. Hydrate forms subdivided according to their morphological features have been shown: powder and layered growth, retained ice shapes, and whisker crystals. The conducted experiments have defined effects of the thermal cycling regime on forms of obtained hydrates: decreased rates of heating/cooling results in an increase of a share of whisker crystals. The rate of decomposition of loose retained ice shapes in the form of hydrate has been defined to be 2.3 times faster than that of powder and dense layered hydrates.

Downhole log evidence for the coexistence of structure II gas hydrate and free gas below the bottom simulating reflector in the South China Sea

Abstract Stratigraphic layered pore-filling gas hydrates are identified above the bottom simulating reflector (BSR) using the well log and core data acquired at Sites W11 and W17 during the third gas hydrate drilling expedition conducted by China's Geological Survey/Guangzhou Marine Geological Survey (GMGS3) in the South China Sea. A seismic profile near Site W17, reveal the presence of two BSRs (i.e., double BSR), which we show to relate to zones of structure I gas hydrate (I-BSR) and structure II gas hydrate (II-BSR). Well log data from Site W17 between the “I-BSR” (projected depth of 250 mbsf) and “II-BSR” (projected depth of 330 mbsf) showed anomalous responses for gas hydrate-bearing sediments with high resistivity, high S-wave velocity, and alternating high and low P-wave velocities. Pressure core data support the interpretation that structure II gas hydrate occurs at a depth of 263 mbsf at Site W17. The cross-plot between log-derived neutron and density porosities reveals a free gas-bearing layer at a depth of 258–270 mbsf, suggesting gas hydrate coexists with free gas between the “I-BSR” and the “II-BSR.” Synthetic seismograms generated from the P-wave velocity and density logs further support the presence of free gas in this section. Based on the coexistence of hydrate, free gas and water, the simplified three-phase equation (STPE) was modified to simultaneously estimate free gas and hydrate saturations beneath the “I-BSR” from P-wave and S-wave velocity logs, assuming uniform or patchy distributions of free gas. The estimated free gas and hydrate saturations, together with gas compositions from pressure core samples, collectively indicate that structure II gas hydrate and free gas are interbedded and coexist below the “I-BSR” at Site W17. Our study of the coexistence of gas hydrate and free gas between the double BSR at Site W17 provides new insights into gas hydrate systems in nature that contain more complex gas chemistries.

Multiphase Flow Behavior of Layered Methane Hydrate Reservoir Induced by Gas Production

Gas hydrates are expected to be a potential energy resource with extensive distribution in the permafrost and in deep ocean sediments. The marine gas hydrate drilling explorations at the Eastern Nankai Trough of Japan revealed the variable distribution of hydrate deposits. Gas hydrate reservoirs are composed of alternating beds of sand and clay, with various conditions of permeability, porosity, and hydrate saturation. This study looks into the multiphase flow behaviors of layered methane hydrate reservoirs induced by gas production. Firstly, a history matching model by incorporating the available geological data at the test site of the Eastern Nankai Trough, which considers the layered heterogeneous structure of hydrate saturation, permeability, and porosity simultaneously, was constructed to investigate the production characteristics from layered hydrate reservoirs. Based on the validated model, the effects of the placement of production interval on production performance were investigated. The modeling results indicate that the dissociation zone is strongly affected by the vertical reservoir’s heterogeneous structure and shows a unique dissociation front. The beneficial production interval scheme should consider the reservoir conditions with high permeability and high hydrate saturation. Consequently, the identification of the favorable hydrate deposits is significantly important to realize commercial production in the future.

Crystal Chemistry of Iron Containing Cementitious AFm Layered Hydrates

The crystal structure of the three main Fe-containing AFm phases (Al2O3-Fe2O3-mono: family of lamellar calcium alumina-ferrite hydrates) encountered in cement hydration process are characterized and compared with their Al-analogs. This includes AFm phases containing sulfate (which is present in Portland cement to regulate the hydration kinetic), carbonate (which is present in Portland cements, or originates from atmospheric carbon oxide) and chloride (either from the water used or from the environment). The results show that Fe-AFm and Al-AFm compounds are not (or rarely) isostructural. Iron in AFm phases does not simply substitute aluminium. Fe-carbonate has a rhombohedral symmetry whereas Al-carbonate has a triclinic symmetry, with carbonate anions located in different crystallographic sites in both compounds. Fe-Friedel’s salt corresponds to a 3R polytype whereas Al-Friedel’s salt corresponds to a 6R polytype. Both compounds have a temperature dependent transition with two different HT- and two different LT-polymorphs descriptions (HT: high-temperature, LT: low-temperature). Only Fesulfate and Al-sulfate are isostructural. Despite this isostructural feature, only limited solid solutions have been observed between both sulfate end-members. In a general way, this system (when considering sulfate, carbonate and chloride with aluminium and iron) leads to extremely complicated subsystems with limited solid solutions. The crystallographic studies and comparisons developed here have been fully completed by thermodynamic characterisations in order to make possible thermodynamic modelling of the hydrates assemblage during the hydration process and the aging of Portland concrete.

Effect of geological layers on hydrate dissociation in natural gas hydrate reservoirs

Naturally occurring reservoirs of methane gas hydrate have been found in arctic and marine environments around the world. They are an attractive source of energy as natural gas can be produced from these hydrate deposits by depressurization or thermal stimulation. Reservoir simulations are used to find the optimum production strategies for methane gas hydrate reservoirs. Most of these simulation are carried out for homogeneous hydrate reservoirs in absence of substantial well data. These gas hydrate reservoirs are inherently heterogeneous because of the geological settings of the hydrate bearing sediments. Majority of the heterogeneity comes from the depositional layering at different geological time scales. Examples are Mount Elbert, block 818 in Gulf of Mexico, Walker Ridge 313 Site. The effects of geological layering on gas production and hydrate dissociation fronts in the reservoir are still unknown. In the present work, a 3-dimensional, multiphase, multi-component, thermal simulator is used to study layered gas hydrate reservoir, underlain by an aquifer, with cross-flow between the layers. Gas production from the reservoir and gas hydrate dissociation fronts in the reservoir are found for different aquifer permeability, different layering and well completions. In layered confined reservoirs, recovery is found to be dependent on (a) the total volume of the hydrate present in the reservoir which governs the enthalpy requirement for dissociation, (b) depressurization potential of the reservoir which depends on the effective permeability and (c) the enthalpy available for dissociation which depends on the reservoir enthalpy and heat transfer from over and under-burden. The layering suggests the positions and progress of the dissociation fronts and affects the gas recovery depending on the aquifer permeability. This effect is seen because of the pressure variation in different layers and enthalpy available for hydrate dissociation. In unconfined reservoirs the effect of layering on dissociation front positions is found to be insignificant as the pressure variation in the layers is insignificant because of the unconfined aquifer. A weakly un-confined aquifer also renders the depressurization ineffective.