Natural Hydrate Research Articles

Mechanical Properties and Strength Criteria of Hydrate-Bearing Sediments Considering Clay Minerals.

Understanding the effect of clay on the mechanical properties and strength criteria of hydrate-bearing sediments (HBS) is essential for evaluating the safety of clay-rich reservoirs. In this study, a series of triaxial shear tests were conducted to investigate the impacts of clay type and content on the mechanical behavior of I-HBS (hydrate-bearing sediments containing illite) and M-HBS (hydrate-bearing sediments containing montmorillonite). The findings reveal that M-HBS exhibit greater susceptibility to strain hardening compared to I-HBS, accompanied by more extensive volume deformation, and both strain hardening and shear shrinkage intensify with increasing clay content. Moreover, the results demonstrate higher failure strength and Young's modulus in I-HBS than M-HBS. The failure strength of sediments is affected by both the clay content and effective confining pressure, with an established relationship between the failure strength and these two factors. Additionally, the cohesion and internal friction angle of sediments exhibit distinct linear correlations with clay content due to variations in the clay type. The Mohr-Coulomb strength criterion incorporating the clay content is established, enabling the prediction of shear strength in clay-rich hydrate reservoirs. The clay type and content are the cause for different strengths and shear mechanisms of sediments. This research holds significant implications for the safe mining of natural gas clay-rich hydrate reservoirs.

(De)hydration Front Propagation Into Zero‐Permeability Rock

AbstractHydration and dehydration reactions play pivotal roles in plate tectonics and the deep water cycle, yet many facets of (de)hydration reactions remain unclear. Here, we study (de)hydration reactions where associated solid density changes are predominantly balanced by porosity changes, with solid rock deformation playing a minor role. We propose a hypothesis for three scenarios of (de)hydration front propagation and test it using one‐dimensional hydro‐mechanical‐chemical models. Our models couple porous fluid flow, solid rock volumetric deformation, and (de)hydration reactions described by equilibrium thermodynamics. We couple our transport model with reactions through fluid pressure: the fluid pressure gradient governs porous flow and the fluid pressure magnitude controls the reaction boundary. Our model validates the hypothesized scenarios and shows that the change in solid density across the reaction boundary, from lower to higher pressure, dictates whether hydration or dehydration fronts propagate: decreasing solid density causes dehydration front propagation in the direction opposite to fluid flow while increasing solid density enables both hydration and dehydration front propagation in the same direction as fluid flow. Our models demonstrate that reactions can drive the propagation of (de)hydration fronts, characterized by sharp porosity fronts, into a viscous medium with zero porosity and permeability; such propagation is impossible without reactions, as porosity fronts become trapped. We apply our model to serpentinite dehydration reactions with positive and negative Clapeyron slopes and granulite hydration (eclogitization). We use the results of systematic numerical simulations to derive a new equation that allows estimating the transient, reaction‐induced permeability of natural (de)hydration zones.

Simultaneous quantification of 2-pyrrolidone-5-carboxylic acid (PCA), urocanic acid (UCA), and histidine (His) in the stratum corneum by HPLC-PDA

Located in the epidermis, the stratum corneum is the most superficial layer of the skin, acting as a barrier against aggression from the external environment, preventing dehydration, and maintaining the water balance of the skin. The stratum corneum contains the Natural Hydration Factor (NMF), a mixture of hygroscopic molecules derived from filaggrin. The NMF includes 2-pyrrolidone-5-carboxylic acid (PCA), urocanic acid (UCA), and histidine (His), target biomarkers that were extracted by tape-stripping from the stratum corneum of participants for quantification in HPLC-PDA. By extracting the stratum corneum, we developed a protocol to optimize, through audience definition, the quantification of NMF biomarkers. Chromatographic analysis was performed using a YMC-Triart C18 chromatographic column, with a gradient elution of mobile phase composed of triethylammonium phosphate and acetonitrile mixture, and a photodiode array detector. HPLC-PDA procedure was selective, linear (in the range from 0.2 to 5.0 µg/mL), accurate (recovery from 92.7 to 115.1 %), precise (RSD from 0.3 to 12.1 %), and with proper detection and quantification limits. The measurement uncertainty was evaluated from validation data, with combined standard uncertainty values of 0.025–0.12 µg/mL (2.1–5.6 %), 0.004–0.28 µg/mL (2.4–12.6 %), and 0.016–0.16 µg/mL (3.2–7.9 %) for His, PCA, and UCA, respectively. Statistical analyses were performed using Monte Carlo simulation and the Mann-Whitney test, as our results were not homoscedastic and deviated from normality. The results indicate that the best audience for quantifying biomarkers were participants up to 35 years old, with all phototypes, and, preferably, female.

Effect of marine clay minerals on the thermodynamics of CH4 hydrate: Evidence for the inhibition effect with implications

Clay minerals are widely distributed in hydrate-bearing sediments worldwide, especially in the clayey-silty sediments in the South China Sea. The debate on the influence of clay on the thermodynamics of natural gas hydrate (NGH) remains and impedes the fundamental understanding of hydrate-clay interactions and the design of effective production strategies for energy recovery. Specifically, the phase equilibria of MH in the presence of clay and how different types of water associated with clay particles affect NGH thermodynamics and stability are not fully elucidated and warrant investigation. In this study, the phase equilibria of methane hydrate (MH) were measured in the presence of typical clays from the South China Sea, i.e., montmorillonite, kaolinite, and illite. The shift of MH phase equilibria curve to a more stringent pressure was identified with Na-montmorillonite showing the most significant inhibition. The leftward shift (inhibition) of phase equilibrium temperature (Teq) is up to 3.9 K at a pressure of 10.40 MPa for Na-montmorillonite compared with pure water. Furthermore, we develop a thermodynamic model based on the classical Chen-Guo model first accounting for the change in water activity (aw) due to cation exchange of Na-montmorillonite. The developed model exhibits good predictability with the measured phase equilibira data. The inhibition on the phase equilibria of MH is linked to the reduction of aw due to the clay-bound water for clays with a swelling nature. The findings of this study offer direct evidence and explanations on how clay minerals thermodynamically inhibit CH4 hydrate. It provides valuable insights into the resource estimation of clayey-silty NGH in nature and facilities the design of suitable production strategies targeting clay-rich hydrate-bearing sediments.

Effect of initial pore water content and salinity on the resistivity of methane hydrate-bearing fine sediments

Methane hydrates are widely distributed in the soft silty-clayey soils of continental margin sediments. The resistivity method is generally used to detect their distribution state and monitor their kinetic reaction process. However, there are some major details to be elaborated on as to the occurrence state and the evolution of key characteristic parameters. Based on the kinetic reaction experiment under different lithological conditions (initial water content and pore water salinity), this research records the changing resistance of natural sand porous medium system during the cooling formation of hydrates by in-situ measurement. The Archie formula is further used to study the influencing factors of the resistance of hydrate-bearing sediments and how the resistance changes during hydrate formation. The results demonstrate that these two lithological parameters can significantly affect the resistivity of the hydrate-bearing natural sand porous media system. It is found that within a certain range, NaCl in pore water will inhibit the formation reaction of hydrates, while an increase of initial water content will enhance the hydrate production amount in the system. With the hydrate formation in the pores, the porosity and skeleton composition of the natural sand porous medium change as well, coupled with the salt-removing effect, which further changes the system resistivity. During hydrate formation, the system resistivity changes regularly in the cooling stage, hydrate nucleation stage, and hydrate formation stage. Our study systematically considers the influence of these geological parameters on resistivity characterization at different reaction stages during the formation of natural hydrates. Thus, it can serve as a technical reference for hydrate reservoir logging and other related issues.

Formation of Natural Magnesium Silica Hydrate (M-S-H) and Magnesium Alumina Silica Hydrate (M-A-S-H) Cement.

Occurrences of natural magnesium alumina silicate hydrate (M-(A)-S-H) cement are present in Feragen and Leka, in eastern and western Trøndelag Norway, respectively. Both occurrences are in the subarctic climate zone and form in glacial till and moraine material deposited on ultramafic rock during the Weichselian glaciation. Weathering of serpentinized peridotite dissolves brucite and results in an alkaline fluid with a relatively high pH which subsequently reacts with the felsic minerals of the till (quartz, plagioclase, K-feldspar) to form a cement consisting of an amorphous material or a mixture of nanocrystalline Mg-rich phyllosilicates, including illite. The presence of plagioclase in the till results in the enrichment of alumina in the cement, i.e., forms M-A-S-H instead of the M-S-H cement. Dissolution of quartz results in numerous etch pits and negative quartz crystals filled with M-A-S-H cement. Where the quartz dissolution is faster than the cement precipitation, a honeycomb-like texture is formed. Compositionally, the cemented till (tillite) contains more MgO and has a higher loss of ignition than the till, suggesting that the cement is formed by a MgO fluid that previously reacted with the peridotite. The M-(A)-S-H cemented till represents a new type of duricrust, coined magsilcrete. The study of natural Mg cement provides information on peridotites as a Mg source for Mg cement and as a feedstock for CO2 sequestration.

Reactive transport modeling of organic carbon degradation in marine methane hydrate systems

Natural methane hydrate has often been observed in sand layers that contain no particulate organic carbon (POC), but are surrounded by organic-rich, fine-grained marine muds. In this paper, we develop a reactive transport model (RTM) of a microbially-mediated set of POC degradation reactions, including hydrolysis of POC driven by extracellular enzymes, fermentation of the resulting high-molecular weight dissolved organic carbon (HMW-DOC), and methanogenesis that consumes low-molecular weight dissolved organic carbon (LMW-DOC). These processes are mediated by two groups of microbes, fermenters and methanogens that are heterogeneously distributed in different lithologies, with the largest numbers of microbes in the large pores of coarse-grained layers. We find that the RTM can reproduce methane hydrate occurrences observed in two different geological environments, at Walker Ridge Site 313-H (Gulf of Mexico) and IODP Site U1325 (Cascadia Margin). We also find that microbes can degrade POC even if they are physically separated, as extracellular enzymes and DOC can diffuse away from where they are produced by microbes. Microbial activity is highest at relatively early times after burial at shallow depths and near lithological boundaries, where concentration gradients transport solutes to intervals that contain the most microbes.

Microstructural Study on Dissolution of Natural Methane Hydrate by Multicontrast and Multiscale X-ray Computed Tomography

Microstructural Study on Dissolution of Natural Methane Hydrate by Multicontrast and Multiscale X-ray Computed Tomography

Synergistic Effect of Hyperactive Antifreeze Protein on Inhibition of Gas-Hydrate Growth by Hydrophobic and Hydrophilic Groups.

Antifreeze proteins (AFPs) are biodegradable inhibitors that effectively prevent the formation of natural gas hydrates that block pipelines. In this study, molecular dynamics simulations were employed to establish a kinetic model of the hyperactive insect antifreeze protein (Tenebrio molitor, TmAFP) and its mutants to inhibit the growth of sI natural methane hydrate. Simulations revealed that the hydrophobic and hydrophilic groups of threonine (Thr) residues at hydrate-binding sites played a synergistic role in binding hydrates. The hydrophobic groups anchored TmAFP to the hydrate surface through residues Thr39-Thr65 by migrating pendant hydrophobic methyl groups to the hydrate semicages. The hydrophilic groups stabilized TmAFP by hydrogen bonding with water molecules and integrating them into a quasi-hydrate structure, which more effectively inhibited hydrate growth. The results suggest that the hydrate growth inhibition is attributed to both the shape complementarity and the flexibility of binding residues. The synergy between hydrophobic and hydrophilic groups provides guidance for the design of more effective hydrate inhibitors.

Molecular dynamics study on the structure and mechanical properties of tobermorite

The calcium silicate hydrate (C-S-H) structure has been indicated its atomic structure in the early stage of hydration resembles the geometry of tobermorite which is a natural calcium silicate hydrate. The mechanical properties of tobermorite crystals were investigated based on molecular dynamics (MD) method in this study. Uniaxial tension simulation in the z-direction was performed to the layered structure of tobermorite 9 Å, 11 Å and 14 Å at molecular level. The stress–strain relationships were obtained, and the structure analysis of tobermorite was carried out in terms of the relative concentration profile and mean square displacement. It has been found that tobermorite 9 Å has the greatest tensile strength compared with tobermorite 11 Å and 14 Å. It also shows that strong interaction between interlayer Ca ions and silicon-oxygen tetrahedra will increase the resistance of tensile loading. These findings may contribute to have a deep knowledge of the intrinsic property of C-S-H.

Pore-Scale Investigation of Decomposition-Methods-Dependent Fluid Flow Properties in Hydrate-Bearing Sediments

Summary Depressurization (PD) and thermal stimulation (TS) are the primary methods for producing gas from natural gas hydrate (NGH) sediments. Fluid flow properties of the hydrate sediment, such as permeability, are fundamental parameters for simulating both processes. Most of the existing formulated permeability models are based on the numerical or experimental investigation of hydrate morphology evolution without considering the decomposition methods. In this study, we investigate the hydrate-decomposition-methods (PD and TS processes)-dependent fluid flow properties of hydrate sediments, which is achieved by microcomputed tomography (micro-CT) scanning of hydrate morphology evolution during PD- and TS-induced decomposition, as well as pore-scale modeling of fluid flow in the extracted 3D fluid-rock-hydrate images. We find that the decomposition behavior during TS is much more complicated than that during PD. The retardation zone in the PD sample increases the heterogeneity of the pore structure, while the secondary hydrates generated during TS cause even more heterogeneity in the pore space. The better facilitation of the TS method on hydrate split is favorable for the continuity of the gas phase. The pore-scale fluid flow simulation shows that the modified Kozeny-Carman (K-C) model is the best to describe the evolution of the normalized permeability with hydrate saturation during PD. However, a single model is not sufficient to describe the normalized permeability during TS decomposition due to the stronger heterogeneous porous structure reformed by the local accumulation of secondary hydrates. The two-phase flow capability is best at the initial stage of PD decomposition, while the two-phase flow region becomes wider as TS decomposition progresses. These results provide significant references for the simulation of the natural hydrate extraction process using different decomposition methods.

Influence of Clay‐Containing Sediments on Methane Hydrate Formation: Impacts on Kinetic Behavior and Gas Storage Capacity

AbstractOn Earth, natural hydrates are mostly encountered in clay‐rich sediments. Yet their formation processes in such matrices remain poorly understood. Achieving an in‐depth understanding of how methane hydrates accumulate on continental margins is key to accurately assess (a) their role in sustaining the development of some chemosynthetic communities at cold seeps, (b) their potential in terms of energy resources and geohazards, and (c) the fate of the methane releases, a powerful greenhouse gas, in this changing climate. This study investigated the formation of methane hydrates and their gas storage capacity (GSC) in clay‐rich sediments. A set of hydrate experiments were performed in matrices composed of sand, illite‐rich clay, and montmorillonite‐rich clay at different proportions aiming to determine the role of mineralogy on hydrate formation processes. The experiments demonstrate that a clay content of 10% in a partially water saturated sand/clay mixture increases the induction time by ∼60%, irrespective of the nature of the clay used. The increase in water saturation in the two matrices promotes hydrate formation. Micro‐Raman spectroscopic analyses reveal that increasing the clay content leads to a decrease in the hydrate small‐cage occupancy, with an impact on the storage capacity. Finally, the analyses of collected natural samples from the Black Sea (off Romania) enable us to estimate the GSC of the deposit. Our estimates is different from previous ones, and supports the importance of coupling multiscale properties, from the microscale to the geological scale, to accurately assess the total amount of methane hosts in hydrate deposits worldwide.

Rapid hydration and weakening of anhydrite under stress: implications for natural hydration in the Earth's crust and mantle

Abstract. Mineral hydration is an important geological process that influences the rheology and geochemistry of rocks and the fluid budget of the Earth's crust and mantle. Constant-stress differential compaction (CSDC) tests, dry and “wet” tests under confining pressure, and axial-stress tests were conducted for the first time to investigate the influence of triaxial stress on hydration in anhydrite–gypsum aggregates. Characterization of the samples before and after triaxial experiments was performed with optical and scanning electron microscopy, including energy-dispersive spectroscopy and electron backscatter diffraction mapping. Stress–strain data reveal that samples that underwent constant-stress differential compaction in the presence of fluids are ∼ 14 % to ∼ 41 % weaker than samples deformed under wet conditions. The microstructural analysis shows that there is a strong temporal and spatial connection between the geometry, distribution, and evolution of fractures and hydration products. The increasing reaction surface area in combination with pre-existing gypsum in a gypsum-bearing anhydrite rock led to rapid gypsification. The crystallographic orientations of newly formed vein gypsum have a systematic preferred orientation for long distances along veins, beyond the grain boundaries of wall-rock anhydrite. Gypsum crystallographic orientations in {100} and {010} are systematically and preferentially aligned parallel to the direction of maximum shear stress (45∘ to σ1). Gypsum is also not always topotactically linked to the wall-rock anhydrite in the immediate vicinity. This study proposes that the selective inheritance of crystal orientations from favourably oriented wall-rock anhydrite grains for the minimization of free energy for nucleation under stress leads to the systematic preferred orientation of large, new gypsum grains. A sequence is suggested for hydration under stress that requires the development of fractures accompanied by localized hydration. Hydration along fractures with a range of apertures up to 120 µm occurred in under 6 h. Once formed, gypsum-filled veins represent weak surfaces and are the locations of further shear fracturing, brecciation, and eventual brittle failure. These findings imply that non-hydrostatic stress has a significant influence on hydration rates and subsequent mechanical strength of rocks. This phenomenon is applicable across a wide range of geological environments in the Earth's crust and upper mantle.

Unraveling the Role of Natural Sediments in sII Mixed Gas Hydrate Formation: An Experimental Study.

Considering the ever-increasing interests in natural gas hydrates, a better and more precise knowledge of how host sediments interact with hydrates and affect the formation process is crucial. Yet less is reported for the effects of sediments on structure II hydrate formation with complex guest compositions. In this study, experimental simulations were performed based on the natural reservoir in Qilian Mountain permafrost in China (QMP) due to its unique properties. Mixed gas hydrates containing CH4, C2H6, C3H8, and CO2 were synthesized with the presence of natural sediments from QMP, with quartz sands, and without sediments under identical p-T conditions. The promoting effects of sediments regardless of the grain size and species were confirmed on hydrate formation kinetics. The ice-to-hydrate conversion rate with quartz sand and natural QMP sediments increased by 23.5% and 32.7%, respectively. The compositions of the initial hydrate phase varied, but the difference became smaller in the resulting hydrate phases, having reached a steady state. Beside the structure II hydrate phase, another coexisting solid phase, neither ice nor structure I hydrate, was observed in the system with QMP sediments, which was inferred as an amorphous hydrate phase. These findings are essential to understand the mixed gas hydrates in QMP and may shed light on other natural hydrate reservoirs with complex gas compositions.

Targeted Repair of Super‐Lubricating Surfaces via Pairing Click Chemistry

AbstractIntact advanced lubricating coatings can rival natural hydration lubricating systems. However, once damaged, their lubricity is drastically diminished as the delaminated coating materials are either unable to re‐bond to the original substrate due to the irreversible bond breakage or easily bridge the opposing rubbing surface via non‐specific interactions. Inspired by the reversibility and selectivity of dynamic click chemistry, super‐lubricating surfaces with targeted self‐repairability are developed through a surface‐recognized strategy. The rubbing surfaces exhibit superlubricity with friction coefficient µ ≈0.002 at physiologically high pressure (≈7.5 MPa). When wear‐induced coating‐substrate breakage occurs, the lubricating materials can target and reassociate with their pairing surfaces through specific dynamic covalent linkages, circumventing surface bridging, and recovering high lubricity even upon repeated damage. This study offers an innovative paradigm for developing durable lubricating surfaces with bespoke reparability for biomedical applications.

Increasing Gas Production of Continuous Freeze-Thaw Hydrate Deposits Based on Local Reservoir Reconstruction

The fracturing technology for increasing gas production based on hydrate reservoir reconstruction has been proven to have the application prospect of hydrate production. The main content of this work is to study the influence mechanism between multiple production wells after fracturing the reservoirs around horizontal wells. Simulation results indicated that the gas production rates and cumulative volume of released gas by using hydraulic fracturing were both higher than that by using the traditional depressurization method. The average gas-to-water ratio in this work has broken through the technical bottleneck of exploiting hydrate only by the traditional depressurization method. After the rock matrix around the horizontal well was fractured, the permeability of the reservoir in the fracturing area would be increased; thus, the propagation distance of pressure drop would be promoted. In addition, the penetration of the hydrate decomposition area between horizontal production wells was conducive to promoting the flow of decomposed gas and water to production wells. Besides, the hydraulic fracturing method to increase the permeability of the reservoir around the production well is very effective for the gas production of low-permeability natural hydrate deposits. The best distance between production wells was recommended to be 45~60 m, and it was recommended to provide appropriate heat in the area between the two wells to accelerate the decomposition of hydrate.

Effect of Pressure on Hydrogen Isotope Fractionation in Methane during Methane Hydrate Formation at Temperatures Below the Freezing Point of Water

Isotopic fractionation of methane between gas and solid hydrate phases provides data regarding hydrate-forming environments, but the effect of pressure on isotopic fractionation is not well understood. In this study, methane hydrates were synthesized in a pressure cell, and the hydrogen isotope compositions of the residual and hydrate-bound gases were determined. The δ2H of hydrate-bound methane formed below the freezing point of water was 5.7–10.3‰ lower than that of residual methane, indicating that methane hydrate generally encapsulates lighter molecules (CH4) instead of CH32H. The fractionation factors αH-V of the gas and hydrate phases were in the range 0.9881–0.9932 at a temperature and pressure of 223.3–268.2 K and 1.7–19.5 MPa, respectively. Furthermore, αH-V increased with increasing formation pressure, suggesting that the difference in the hydrogen isotopes of the hydrate-bound methane and surrounding methane yields data regarding the formation pressure. Although the differences in the hydrogen isotopes observed in this study are insignificant, precise analyses of the isotopes of natural hydrates in the same area enable the determination of the pressure during hydrate formation.

Ferromagnetic shape memory alloy Ni52.5Mn22.5Ga25: Phase transformation at high pressure and effects on natural gas hydration

Ferromagnetic shape memory alloy NiMnGa was used to prepare the micro/nano fluid which has a potential role during the formation of natural gas hydrate (NGH). In the present work, phase transformations of Ni52.5Mn22.5Ga25 micro/nano particles under various pressures, and the crystal structure before and after participating in the natural gas hydration were investigated. The effect of the micro/nano fluid containing Ni52.5Mn22.5Ga25 particles on the formation heat of NGH was studied. It was worked out that Ni52.5Mn22.5Ga25 particles exhibit a high stability both in phase transformation below 15 MPa pressure and crystal structure after natural gas hydration. The fluid containing Ni52.5Mn22.5Ga25 particles can reduce the hydration reaction temperature and promote the formation of NGH.

Effect of geomechanics and of grid discretization on the predictions of production from natural hydrate deposits and of the associated geomechanical system response

Effect of geomechanics and of grid discretization on the predictions of production from natural hydrate deposits and of the associated geomechanical system response

Gas Hydrates: Applications and Advantages

Gas hydrates are promising components for a wide range of industries and the national economy. This paper outlines the gas hydrate application areas with the greatest potential. Gas hydrates of methane, ethane, propane, carbon dioxide and freon were investigated. Double gas hydrates were found to be coming into use. Natural and artificial hydrates are now being exploited. The main properties and component composition of hydrates, as well as their extraction methods are described. The key aspects of using hydrates in the energy industry, gas chemistry and petrochemistry, heat exchange systems and fire safety management are highlighted. These specific aspects were identified by analyzing the known experimental findings, results of mathematical modeling, bench and field tests, as well as trial runs of industrial systems. The recent advances in science and technology in this field were analyzed. The range of tasks that need to be tackled to improve the efficiency of using gas hydrates are defined.