Research advances on the dissociation dynamics of natural gas hydrates

Natural gas hydrate is a kind of clean energy with great development potential but is still not commercially developed due to the bottlenecks such as exploitation technology, economical efficiency, and environmental effects.In recent years, people have explored the application of hydrate technology in the field of CO2 capture, seawater desalination, energy storage, gas separation, etc. One of the most challenging and critical problems is how the hydrates are formed and decomposed at any time. This paper summarizes the fundamental research on hydrate decomposition dynamics, including hydrate decomposition properties, influencing factors, and dissociation mechanisms. Moreover, the paper reviews the development of hydrate dissociation dynamics models. The existing models are divided into four categories according to dissociation mechanisms: Thermal dissociation models, intrinsic dynamics models, mass transfer dissociation models and integrated models, and their assumptions, main understanding and limitations are highlighted. Future directions for improving hydrate dissociation dynamics research are foreseen to deepen the understanding of hydrate dissociation dynamics and promote the development and utilization of hydrates

Temperature and salinity effects on the Raman scattering cross section of the water OH-stretching vibration band in NaCl aqueous solutions from 0 to 300 °C

International audienceWater is often used as an internal standard in quantitative Raman spectroscopic measurements of dissolved species in aqueous solutions containing salts at varying temperatures. However, the effects of temperature and dissolved ions on the relative differential Raman scattering cross section (RSCS) of the OH stretching vibration band of water at elevated temperatures and salinities are not well defined quantitatively. In this study, the Raman spectra of NaCl solutions with different salinity (from 0 to 5 mol NaCl/kg·H2O) at 20 o C at atmospheric pressure and from 0 to 300 o C at 30 MPa were studied. The relative RSCS of the OH stretching vibration band of liquid water (σ(mNaCl, T, 30 MPa)/σ(Pure water, 20 o C, 30 MPa)) as a function of temperature (T, in o C) and salinity (mNaCl, in mol/kg·H2O) was established: σ(mNaCl, T, 30 MPa) /σ(Pure water, 20 o C, 30 MPa) = f (T, mNaCl) = a(T-20) + b where a = 0.000089 × mNaCl 1/2-0.001164; b = 0.0355 × mNaCl + 1; The RSCS of the OH stretching vibration band of water in pseudo back-scattering geometry decreases linearly with increasing temperature, but increases with the addition of dissolved NaCl within the whole temperature range. The enhancement factor of the RSCS by dissolved NaCl increases with temperature. Such effects of temperature and salinity should be considered in quantitative Raman spectroscopic study of species concentration in aqueous solution at high temperature when using water as internal standard

Significance of paleo-fluid in the Ordovician–Silurian detachment zone to the preservation of shale gas in western Hunan–Hubei area

The studies on the paleo-fluid in the Ordovician–Silurian detachment zone in the Middle–Upper Yangtze area focus on the origin of high-density methane inclusions and the evolution process of formation pressure, but rarely deal with the significance of paleo-fluid to shale gas preservation. In this paper, the relationship between fracture formation and detachment zone was analyzed by observing the Ordovician–Silurian outcrops in western Hunan–Hubei area and by investigating the geological characteristics of fracture veins in the drilling cores. Then, the significance of paleo-fluid forming environment and detachment zone to shale gas preservation was studied by using inclusion compositions of fracture veins and homogenization temperature test data. Finally, accumulation–dispersion modes of shale gas in the detachment zone were established. The following results were obtained. First, the detachment zone is lithologically composed of silicite with intercalated shale at the Ordovician–Silurian interface. In the detachment zone, rocks are broken and small crumples are developed. The conjugate-vertical joints are relatively developed in the silicite above and below the detachment zone. Second, multi-stage and multi-type inclusions, especially the aqueous inclusions, are developed in the veins of the detachment zone. Third, the infiltration depth of ancient meteoric water along the detachment zone in the study area is over 4000 m. High-density overpressure methane inclusions were captured in the detachment zone during early stage, while normal-pressure methane and nitrogen inclusions were captured during late stage. Fourth, the ionic constituents of inclusions recording the fluid activity during the late stage was characterized by high sodium-chloride coefficient, high desulfurization coefficient and low metamorphic coefficient, and it is indicated that the sealing capacity of the shale in the detachment zone gets worse. Fifth, the accumulation and dispersion of shale gas in the detachment zone within the study area is divided into three modes, i.e., syncline, broad anticline and closed anticline. In conclusion, the detachment zone in the study area is permeable. Synclines and closed anticlines developed in detachment structures are unfavorable for the accumulation of shale gas, while broad anticlines are favorable. Keywords: Western Hunan–Hubei area, Ordovician, Silurian, Detachment zone, Paleo-fluid, Inclusions, Homogenization temperature, Ionic constituent, Shale gas, Preservation conditio

Carbon and oxygen isotope composition of carbonate in bulk sediment in the southwest Taiwan Basin, South China Sea: Methane hydrate decomposition history and its link to mud volcano eruption

Anaerobic oxidation of methane (AOM) coupled with sulfate reduction (SR) generates authigenic carbonate which has the unique carbon and oxygen isotope composition in sulfate methane transition zone (SMTZ). The carbon and oxygen isotope composition of carbonate in sediments, which can be used to revel the variable methane flux, is affected by the percentage of AOM-driven carbonate in sediments. To investigate the methane hydrate decomposition history in the southwest Taiwan Basin, we analyzed a 13 m-long sediment core for grain size, carbonate and elemental carbon contents and stable carbon and oxygen isotopes composition of carbonate (δ13Ccarb and δ18Ocarb). The AMS 14C dating results and carbonate content reveal that a turbidity current occurred at around 14 ka B.P., which reversed sediment accumulation between 455 and 885 cm in depth. Combining the chronological framework and δ13Ccarb values, we identified that the methane hydrate decomposition scale began to decrease at 14 ka B.P. Moreover, we discovered that three transiently enhanced methane hydrate decomposition events occurred from then on. Although the δ13Ccarb and δ18Ocarb variability are as expected, the low δ18Ocarb values are inconsistent with the previous theory which favors 18O-enriched in AOM-driven authigenic carbonate. Thus, we suggest that a large amount of 18O-depleted water which originally migrated from southwest Taiwan island was injected into surface sediment along with the eruption of mud volcanos. As the terminal electron accepter of AOM-SR reaction, the exogenous 18O-depleted water leads its special oxygen isotope to be inherited by the authigenic AOM-driven carbonate. The proposed theory provides new insights on the authigenic carbonate in methane hydrate area and the association between methane hydrates and mud volcanoes

Lipid Distribution in Marine Sediments from the Northern South China Sea and Association with Gas Hydrate

National Major Fundamental Research and Development Project of China ( [2009CB219501]; National Natural Science Foundation of China [40976035, 41276046]The distributions of lipids in surface and subsurface sediments from the northern South China Sea were determined. The n-alkanes were in bimodal distribution that is characterized by a centre at n-C-16-n-C-20 with maximum at C-18 (or C-19) and n-C-27-n-C-31 as well as at C-29 (or C-31). The short-chain alkanes suffered from significant losses due to their slow deposition in the water column, and their presence with a slight even carbon predominance in shallow seafloor sediments was ascribed mainly to the direct input from the benthos. The long-chain alkanes with odd predominance indicate transportion of terrigenous organic matter. Immature hopanoid biomarkers reflect the intense microbial activity for bacteria-derived organic matter and the gradual increase of maturity with burial depth. Abundant n-fatty acid methyl esters (n-FAMEs) that are in distributions coincident with fatty acids were detected in all samples. We proposed that the observed FAMEs originated from the methyl esterification of fatty acids; methanol production by methanotrophs and methanogenic archaea related to the anaerobic oxidation of methane, and sulfate reduction provided an O-methyl donor for methylation of fatty acids. The CH4 released from hydrate dissociation at oxygen isotope stage II of Cores ZD3 and ZS5, which had been confirmed by the occurrence of negative C-13 excursion and spherical pyrite aggregates, could have accelerated the above process and thus maximized the relative content of FAMEs at ZD3-2 (400-420 cm depth) and ZS5-2 (241-291 cm depth)

The dynamic behavior of gas hydrate dissociation by heating in tight sandy reservoirs: A molecular dynamics simulation study

Knowledge on the kinetics of gas hydrate dissociation in microporous sediments is very important for developing safe and efficient approaches to gas recovery from natural gas hydrate (NGH) deposits. Herein, molecular dynamics (MD) simulations are used to study the dissociation kinetics in microporous sediments. The hydrate phase occupies a confined sandy nanopore formed by two hydroxylated silica surfaces with a buffering water layer between the hydrate and silica phase, meanwhile, this system is in contact with the bulk phase outside the pore. The hydrates in this sediment system dissociate layer-by-layer in a shrinking core manner. The released methane molecules aggregate and eventually evolve into nanobubbles, most of which are spherical cap-shaped on the hydroxylated silica surfaces. At high initial temperatures, a faster decomposition of the hydrate phase is observed, however, fewer methane molecules migrate to the bulk phase from the pore phase. These phenomena may occur because more methane molecules are released from the hydrate phase and facilitate the formation of nanobubbles with large heat injection; these nanobubbles can stably adsorb on the surface of silica and capture the surrounding methane molecules, thereby decreasing the number of methane molecules in the water phase. In addition, the injection speed of heat flow should be significantly increased at high dissociation temperatures when using the thermal stimulation method to extract gas from hydrates in tight sediments. This study provides molecular level insight into the kinetic mechanism of hydrate dissociation and theoretical guidance for gas production by thermal injection from sediments with low permeabilities.Accepted Author ManuscriptEngineering Thermodynamic

SIRT5 deficiency enhances the proliferative and therapeutic capacities of adipose‐derived mesenchymal stem cells via metabolic switching

Abstract Background Mesenchymal stem cells (MSCs) have therapeutic potential for multiple ischemic diseases. However, in vitro expansion of MSCs before clinical application leads to metabolic reprogramming from glycolysis to oxidative phosphorylation, drastically impairing their proliferative and therapeutic capacities. This study aimed to define the regulatory effects of Sirtuin 5 (SIRT5) on the proliferative and therapeutic functions of adipose‐derived MSCs (ADMSCs) during in vitro expansion. Methods ADMSCs were isolated from wild‐type (WT) and Sirt5‐knockout (Sirt5−/−) mice. Cell counting assay was used to investigate the proliferative capacities of the ADMSCs. Dihydroethidium and senescence‐associated β‐galactosidase stainings were used to measure intracellular ROS and senescence levels. Mass spectrometry was used to analyze protein succinylation. Oxygen consumption rates and extra cellular acidification rates were measured as indicators of mitochondrial respiration and glycolysis. Metabolic‐related genes expression were verified by quantitative PCR and western blot. Hind limb ischemia mouse model was used to evaluate the therapeutic potentials of WT and Sirt5−/− ADSMCs. Results SIRT5 protein levels were upregulated in ADMCs during in vitro expansion. Sirt5−/− ADMSCs exhibited a higher proliferation rate, delayed senescence, and reduced ROS accumulation. Furthermore, elevated protein succinylation levels were observed in Sirt5−/− ADMSCs, leading to the reduced activity of tricarboxylic acid cycle‐related enzymes and attenuated mitochondrial respiration. Glucose uptake, glycolysis, and pentose phosphate pathway were elevated in Sirt5−/− ADMSCs. Inhibition of succinylation by glycine or re‐expression of Sirt5 reversed the metabolic alterations in Sirt5−/‐ ADMSCs, thus abolishing their enhanced proliferative capacities. In the hind limb ischemia mouse model, SIRT5−/− ADMSCs transplantation enhanced blood flow recovery and angiogenesis compared with WT ADMSCs. Conclusions Our results indicate that SIRT5 deficiency during ADMSC culture expansion leads to reversed metabolic pattern, enhanced proliferative capacities, and improved therapeutic outcomes. These data suggest SIRT5 as a potential target to enhance the functional properties of MSCs for clinical application

Right ventricle segmentation from cardiac MRI: A collation study

© 2014 Elsevier B.V. Magnetic Resonance Imaging (MRI), a reference examination for cardiac morphology and function in humans, allows to image the cardiac right ventricle (RV) with high spatial resolution. The segmentation of the RV is a difficult task due to the variable shape of the RV and its ill-defined borders in these images. The aim of this paper is to evaluate several RV segmentation algorithms on common data. More precisely, we report here the results of the Right Ventricle Segmentation Challenge (RVSC), concretized during the MICCAI\u2712 Conference with an on-site competition. Seven automated and semi-automated methods have been considered, along them three atlas-based methods, two prior based methods, and two prior-free, image-driven methods that make use of cardiac motion. The obtained contours were compared against a manual tracing by an expert cardiac radiologist, taken as a reference, using Dice metric and Hausdorff distance. We herein describe the cardiac data composed of 48 patients, the evaluation protocol and the results. Best results show that an average 80% Dice accuracy and a 1. cm Hausdorff distance can be expected from semi-automated algorithms for this challenging task on the datasets, and that an automated algorithm can reach similar performance, at the expense of a high computational burden. Data are now publicly available and the website remains open for new submissions (http://www.litislab.eu/rvsc/)