Research progress and scientific challenges in the depressurization exploitation mechanism of clayey-silt natural gas hydrates in the northern South China Sea

Natural gas hydrate reservoirs in the northern South China Sea primarily comprise clayey silt, making exploitation more challenging relative to sandy reservoirs in other countries and regions. This paper provides an overview of the latest research developments in the exploitation mechanism covering the past five years, focusing on hydrate phase transition, multiphase flow in the decomposition zone, the seepage regulation of reservoir stimulation zone, and production capacity simulation, all of which are relevant to the previously conducted two rounds of hydrate trial production in offshore areas of China. The results indicate that the phase transition of clayey-silt hydrate remains in a dynamic equilibrium, with the decomposition efficiency mainly controlled by the coupling of heat and flow and high heat consumption during decomposition. The decomposition zone exhibits strong hydrophilicity, easy adsorption, and sudden permeability changes. A temperature drop is present that is concentrated near the wellbore, and once a water lock has formed, the gas-phase flow capacity significantly decreases, leading to potential secondary hydrate formation. To enhance permeability and increase production, it is imperative to implement reservoir and temperature field reconstruction based on initial formation alterations, which will further optimize and improve the transport capacity of the reservoir.Document Type: Current minireviewCited as: Lu, C., Qin, X., Sun, J., Wang, R., Cai, J. Research progress and scientific challenges in the depressurization exploitation mechanism of clayey-silt natural gas hydrates in the northern South China Sea. Advances in Geo-Energy Research, 2023, 10(1): 14-20. https://doi.org/10.46690/ager.2023.10.0

Experimental study on the isothermal adsorption of methane gas in natural gas hydrate argillaceous silt reservoir

Gas hydrate occurs in hydrate reservoirs in a solid form. At present, the conventional exploitation method is to decompose solid hydrate and then extract the resulting gaseous gas. Therefore, the occurrence law of gas in a reservoir is of great significance for the study of gas hydrate seepage and productivity. Adsorption, as an important occurrence mode, has been widely concerned in the research on shale reservoirs. However, the adsorption problem in hydrate reservoirs has not received enough attention. In this paper, the existence of adsorption in a hydrate reservoir has been experimentally confirmed for the first time. Based on the argillaceous silt of a natural gas hydrate reservoir in the South China Sea, the pore structure and adsorption characteristics of argillaceous silt were experimentally studied, and the results were compared with those of typical shale reservoirs. The modified Langmuir and Dubinin-Radushevich equations were used to fit the adsorption data, and the suitable adsorption model of argillaceous silt was established and optimized. The results showed that the inhomogeneous slit pores are dominant in argillaceous silt, and they are formed by the accumulation of lamellar particles. Compared with shale, the adsorption capacity of argillaceous silt is weak under the same conditions. However, adsorption is a spontaneous exothermic reaction, and the ambient temperature of argillaceous silt is much lower than that of shale. Therefore, it is possible for argillaceous silt to achieve an adsorption capacity comparable to that of shale. The modified Langmuir model can be used to simulate argillaceous silt adsorption at low pressure, while under medium and high pressures, the modified Dubinin-Radushevich model performs better. The adsorption capacity of argillaceous silt is affected by moisture. When the water content is 20%, the Langmuir adsorption capacity and the Dubinin-Radushevich maximum adsorption capacity decreases by 21.88% and 13.67%, respectively, which is far less than the influence of moisture on shale adsorption, as reported in the literature.Cited as: Qi, R., Qin, X., Lu, C., Ma, C., Mao, W., Zhang, W. Experimental study on the isothermal adsorption of methane gas in natural gas hydrate argillaceous silt reservoir. Advances in Geo-Energy Research, 2022, 6(2): 143-156. https://doi.org/10.46690/ager.2022.02.0

Maternal perception of child weight and concern about child overweight mediates the relationship between child weight and feeding practices:Does child’s weight predict maternal feeding practices?

Objective:To examine the mediating effects of maternal perception of child weight (weight perception) and concern about overweight (weight concern) on the paths between child weight and maternal feeding practices.Setting:Pudong District, Shanghai, China.Participants:A convenience sample of 1164 mothers who were primary caregivers of preschool children.Results:Sixty per cent of the mothers perceived their overweight/obese children as normal weight or even underweight. The disagreement between actual child weight and maternal weight perception was statistically significant (Kappa = 0·212, P &lt; 0·001). Structural equation modelling indicated that weight perception fully mediated the relationship between child BMI Z-scores and pressure to eat. Weight concern fully mediated the relationships between child BMI Z-scores and the other three feeding practices. The serial mediating effects of weight perception and concern were statistically significant for the paths between child BMI Z-score and monitoring (β = 0·035, P &lt; 0·001), restriction (β = 0·022, P &lt; 0·001), and food as a reward (β = –0·017, P &lt; 0·05).Conclusion:Child weight may influence maternal feeding practices through weight perception and concern. Thus, interventions are needed to increase the accuracy of weight perception, which may influence several maternal feeding practices and thereby contribute to child health.</p

The impact of mineral compositions on hydrate morphology evolution and phase transition hysteresis in natural clayey silts

The authors are grateful to the National Natural Science Foundation of China, China [51991365]; China Geological Survey Project, China [DD20211350]; Guangdong Major Project of Basic and Applied Basic Research, China [2020B0301030003]; Key Program of Marine Economy Development (Six Marine Industries) of Special Foundation of Department of Natural Resources of Guangdong Province, China [2021]56.Peer reviewedPublisher PD

Investigation of the impact of threshold pressure gradient on gas production from hydrate deposits

Acknowledgements The authors are grateful to the National Natural Science Foundation of China (51991365), Key Special Project for Introduced Talents Team of Southern Marine 612 Science and Engineering Guangdong Laboratory (Guangzhou)(GML2019ZD0105) and Key Program of Marine Economy Development (Six Marine Industries) Special 614 Foundation of Department of Natural Resources of Guangdong Province [2021]056 China Geological Survey Project (No. DD20211350).Peer reviewedPostprin

Biochemical and Structural Characterization of the First-Discovered Metazoan DNA Cytosine-N4 Methyltransferase From the Bdelloid Rotifer Adineta vaga

Much is known about the generation, removal, and roles of 5-methylcytosine (5mC) in eukaryote DNA, and there is a growing body of evidence regarding N6-methyladenine, but very little is known about N4-methylcytosine (4mC) in the DNA of eukaryotes. The gene for the first metazoan DNA methyltransferase generating 4mC (N4CMT) was reported and characterized recently by others, in tiny freshwater invertebrates called bdelloid rotifers. Bdelloid rotifers are ancient, apparently asexual animals, and lack canonical 5mC DNA methyltransferases. Here, we characterize the kinetic properties and structural features of the catalytic domain of the N4CMT protein from the bdelloid rotifer Adineta vaga. We find that N4CMT generates high-level methylation at preferred sites, (a/c)CG(t/c/a), and low-level methylation at disfavored sites, exemplified by ACGG. Like the mammalian de novo 5mC DNA methyltransferase 3A/3B (DNMT3A/3B), N4CMT methylates CpG dinucleotides on both DNA strands, generating hemimethylated intermediates and eventually fully methylated CpG sites, particularly in the context of favored symmetric sites. In addition, like DNMT3A/3B, N4CMT methylates non-CpG sites, mainly CpA/TpG, though at a lower rate. Both N4CMT and DNMT3A/3B even prefer similar CpG-flanking sequences. Structurally, the catalytic domain of N4CMT closely resembles the Caulobacter crescentus cell cycle-regulated DNA methyltransferase. The symmetric methylation of CpG, and similarity to a cell cycle-regulated DNA methyltransferase, together suggest that N4CMT might also carry out DNA synthesis-dependent methylation following DNA replication

Investigation of energetic ion losses induced by long-lived saturated internal mode with energetic particle diagnostics in the HL-2A tokamak

ORCID　0000-0002-7547-701XSeveral sets of energetic particle diagnostics, including a set of neutron flux monitoring systems, a solid-state neutral particle analyzer and a fast ion loss probe (FILP), have been used to investigate the energetic ion losses induced by the long-lived saturated internal mode (LLM) in the HL-2A tokamak. Clear experimental evidence for different levels of energetic ion losses induced by LLM, sawtooth and minor disruption has been observed. A numerical calculation for the evolution of neutron emissions was carried out with the FBURN code, and it shows that the neutron emission drop rate linearly increases with the LLM amplitude and no threshold perturbation amplitude exists, illustrating that the loss mechanism for LLM induced energetic ion loss is dominantly convective. In addition, measurement results of the FILP demonstrate that LLM tends to expel energetic ions with relatively low energy ($E \lt 27\,$keV) and high pitch angle ($\theta\gt60^{\circ}$), and can suppress the prompt loss of energetic ions with high energy and low pitch angle to a certain degree. Furthermore, the physical process for LLM induced energetic ion loss can be explained by orbit calculations, which show that LLM induced lost energetic ions will transport from center to peripheral region first, and then get lost out of plasma. The experimental observations are successfully reproduced by calculations using the ORBIT code combined with both the NUBEAM code and the MARS-K code. The paper clearly describes the whole physical process of LLM induced energetic ion loss for the first time in the HL-2A tokamak.journal articl

Intervening Effects of Total Alkaloids of Corydalis saxicola Bunting on Rats With Antibiotic-Induced Gut Microbiota Dysbiosis Based on 16S rRNA Gene Sequencing and Untargeted Metabolomics Analyses

Gut microbiota dysbiosis induced by antibiotics is strongly connected with health concerns. Studying the mechanisms underlying antibiotic-induced gut microbiota dysbiosis could help to identify effective drugs and prevent many serious diseases. In this study, in rats with antibiotic-induced gut microbiota dysbiosis treated with total alkaloids of Corydalis saxicola Bunting (TACS), urinary and fecal biochemical changes and cecum microbial diversity were investigated using 16S rRNA gene sequencing analysis and untargeted metabolomics. The microbial diversity results showed that 10 genera were disturbed by the antibiotic treatment, and two of them were obviously restored by TACS. The untargeted metabolomics analysis identified 34 potential biomarkers in urine and feces that may be the metabolites that are most related to the mechanisms underlying antibiotic-induced gut microbiota dysbiosis and the therapeutic effects of TACS treatment. The biomarkers were involved in six metabolic pathways, comprising pathways related to branched-chain amino acid (BCAA), bile acid, arginine and proline, purine, aromatic amino acid, and amino sugar and nucleotide sugar metabolism. Notably, there was a strong correlation between these metabolic pathways and two gut microbiota genera (g__Blautia and g__Intestinibacter). The correlation analysis suggested that TACS might synergistically affect four of these metabolic pathways (BCAA, bile acid, arginine and proline, and purine metabolism), thereby modulating gut microbiota dysbiosis. Furthermore, we performed a molecular docking analysis involving simulating high-precision docking and using molecular pathway maps to illuminate the way that ligands (the five main alkaloid components of TACS) act on a complex molecular network, using CYP27A1 (a key enzyme in the bile acid synthesis pathway) as the target protein. This study provides a comprehensive overview of the intervening effects of TACS on the host metabolic phenotype and gut microbiome in rats with gut microbiota dysbiosis, and it presents new insights for the discovery of effective drugs and the best therapeutic approaches

Arbitrage in the Hermite Binomial Market

Much attention has been paid to the arbitrage opportunities in the Black–Scholes model when it is driven by fractional Brownian motions. It is natural to ask whether there exists arbitrage or not when we focus on other fractional processes, such as the Hermite process. We set forth an approximation of the Hermite Black–Scholes model by random walks in the Skorokhod topology, and apply the Donsker type approximation to the Hermite process as the Hurst index is greater than 12. We find that the binary model approximation of the Black–Scholes model driven by Hermite processes also admits arbitrage opportunities. Several numerical examples of the Hermite binomial model are presented as demonstration. Moreover, we provide an option pricing model when the geometric Hermite processes drives the price fluctuations of the underlying asset

Arbitrage in the Hermite Binomial Market

Much attention has been paid to the arbitrage opportunities in the Black&ndash;Scholes model when it is driven by fractional Brownian motions. It is natural to ask whether there exists arbitrage or not when we focus on other fractional processes, such as the Hermite process. We set forth an approximation of the Hermite Black&ndash;Scholes model by random walks in the Skorokhod topology, and apply the Donsker type approximation to the Hermite process as the Hurst index is greater than 12. We find that the binary model approximation of the Black&ndash;Scholes model driven by Hermite processes also admits arbitrage opportunities. Several numerical examples of the Hermite binomial model are presented as demonstration. Moreover, we provide an option pricing model when the geometric Hermite processes drives the price fluctuations of the underlying asset