Methane hydrate formation in porous media:Overview and perspectives

Natural gas hydrate(NGH)has recently received more attention as a cleaner alternative energy source that not only reduces carbon emissions caused by the use of conventional fossil fuels but also plays a key role in global climate change.Furthermore,hydrate-based technologies,particularly hydrate-based carbon capture and storage,have enormous promise for decreasing global carbon emissions,and porous media play an important role in all hydrate-based technologies.Accordingly,this paper reviews the recent applications of porous media in the field of methane hydrate(MH)formation and analyzes the influence of porous media systems on MH phase equilibria and formation kinetics.This is because the efficiency of hydrate-based technologies is determined mainly by the phase equilibrium and formation kinetics of hydrates.The influence of the nature of the media on MH formation in porous media systems is comprehensively summarized to understand how porous media can efficiently enhance the kinetics of hydrate formation.Promoters are necessary for rapid hydrate formation,and the effect of various promoters on MH formation was also evaluated.Based on the aforementioned overview and understanding,the mechanisms for MH formation in various porous media systems are proposed.Finally,the future perspectives and challenges of hydrate-based technologies in tackling global climate change were discussed.This review provides a fundamental understanding of the application and development of porous media in rapid hydrate formation,a fair evaluation of the performance of various porous media systems,and critical insights into major research foci.

Large-scale model test study on the water pressure resistance of construction joints of karst tunnel linings

Model tests and numerical calculations were adopted based on the New Yuanliangshan tunnel project to investigate the water pressure resistance of lining construction joints in high-pressure and water-rich karst tunnels.A large-scale model test was designed and conducted,innovatively transforming the external water pressure of the lining construction joint into internal water pressure.The effects of the embedded position and waterstop type on the water pressure resistance of the construction joint were analyzed,and the reliability of the model test was verified via numerical calculations.The results show that using waterstops can significantly improve the water pressure resistance of lining construction joints.The water pressure resistance of the lining construction joint is positively correlated with the lining thickness and embedded depth of the waterstop.In addition,the type of waterstop significantly influences the water pressure resistance of lining construction joints.The test results show that the water pressure resistance of the embedded transverse reinforced waterstop is similar to that of the steel plate waterstop,and both have more advantages than the rubber waterstop.The water pressure resistance of the construction joint determined via numerical calculations is similar to the model test results,indicating that the model test results have high accuracy and reliability.This study provides a reference for similar projects and has wide applications.

Design,modeling and experiments of broadband tristable galloping piezoelectric energy harvester

Galloping based piezoelectric energy harvester is a kind of micro-environmental energy harvesting device based on flowinduced vibrations.A novel tristable galloping-based piezoelectric energy harvester is constructed by introducing a nonlinear magnetic force on the traditional galloping-based piezoelectric energy harvester.Based on Euler-Bernoulli beam theory and Kirchhoff’s law,the corresponding aero-electromechanical model is proposed and validated by a series of wind tunnel experiments.The parametric study is performed to analyse the response of the tristable galloping-based piezoelectric energy harvester.Numerical results show that comparing with the galloping-based piezoelectric energy harvester,the mechanism of the tristable galloping-based piezoelectric energy harvester is more complex.With the increase of a wind speed,the vibration of the bluff body passes through three branches:intra-well oscillations,chaotic oscillations,and inter-well oscillations.The threshold wind speed of the presented harvester for efficiently harvesting energy is 1.0 m/s,which is decreased by 33% compared with the galloping-based piezoelectric energy harvester.The maximum output power of the presented harvester is 0.73 mW at 7.0 m/s wind speed,which is increased by 35.3%.Compared with the traditional galloping-based piezoelectric energy harvester,the presented tristable galloping-based piezoelectric energy harvester has a better energy harvesting performance from flow-induced vibrations.

Progress in use of surfactant in nearly static conditions in natural gas hydrate formation

Natural gas hydrate is an alternative energy source with a great potential for development.The addition of surfactants has been found to have practical implications on the acceleration of hydrate formation in the industrial sector.In this paper,the mechanisms of different surfactants that have been reported to promote hydrate formation are summarized.Besides,the factors influencing surfactant-promoted hydrate formation,including the type,concentration,and structure of the surfactant,are also described.Moreover,the effects of surfactants on the formation of hydrate in pure water,brine,porous media,and systems containing multiple surfactants are discussed.The synergistic or inhibitory effects of the combinations of these additives are also analyzed.Furthermore,the process of establishing kinetic and thermodynamic models to simulate the factors affecting the formation of hydrate in surfactant-containing solutions is illustrated and summarized.

CO_(2) capture using membrane contactors:a systematic literature review

With fossil fuel being the major source of energy,CO_(2) emission levels need to be reduced to a minimal amount namely from anthropogenic sources.Energy consumption is expected to rise by 48%in the next 30 years,and global warming is becoming an alarming issue which needs to be addressed on a thorough technical basis.Nonetheless,exploring CO_(2) capture using membrane contactor technology has shown great potential to be applied and utilised by industry to deal with post-and pre-combustion of CO_(2).A systematic review of the literature has been conducted to analyse and assess CO_(2) removal using membrane contactors for capturing techniques in industrial processes.The review began with a total of 2650 papers,which were obtained from three major databases,and then were excluded down to a final number of 525 papers following a defined set of criteria.The results showed that the use of hollow fibre membranes have demonstrated popularity,as well as the use of amine solvents for CO_(2) removal.This current systematic review in CO_(2) removal and capture is an important milestone in the synthesis of up to date research with the potential to serve as a benchmark databank for further research in similar areas of work.This study provides the first systematic enquiry in the evidence to research further sustainable methods to capture and separate CO_(2).

Foreword

This article serves as the introduction and overview to the Journal of Earth Science＇s special issue concerning unconven- tional oil and gas resources, compiled in October 2017. The compilation includes 17 articles addressing diverse topics re- lated to unconventional oil and gas resources that were pub- lished by Journal of Earth Science （YES）. Each article included in the compilation represents a stand-alone analysis and re- search on a relevant topic that has passed the journal＇s rigorous peer-review editorial system. Collectively, these articles pro- vide key insight to the progress being made towards better understanding of new techniques in unconventional oil and gas resources.