Insights into climate-driven evolution of gas hydrate-bearing permafrost sediments

Massive reserves of natural gas hydrates exist in permafrost and marine sediments. Dissociation of natural gas hydrates could result in enhanced emissions of methane to the atmosphere, aggravating global warming. It may also become a serious geohazard to the geomechanical stability of gas hydrate deposits. The environmental and infrastructural impacts due to climate-driven and human-induced dissociation of natural gas hydrates cannot be well predicted unless we have an accurate estimation of hydrates deposited in both marine and permafrost sediments. However, conventional seismic techniques cannot give reliable estimations of gas hydrates in permafrost sediments as they are unable to distinguish ice from hydrates due to their almost identical acoustic properties. The main objective of this thesis is to address the above challenge via shedding light on the influence of the hydrates presence on the evolution of gas hydrate-bearing permafrost sediments, and developing a coupled geophysical-geothermal scheme, for the first time, for estimation of hydrates saturation in these sediments. To achieve this, magnetic resonance imaging (MRI) was employed to investigate the kinetics of formation and spatial characteristics of methane hydrate in synthetic and natural sediment samples. The analysis of the images acquired during three consecutive thermally-induced hydrate formation/dissociation cycles indicated that in addition to the kinetics of formation, pore-scale distribution of hydrates is affected by the thermal history of the system and the host sediment type, characteristics, and particle size distribution. The results also showed that different hydrate pore-scale habits may co-exist in the system, which is essential to be considered in the models developed for the estimation of the physical properties of gas hydrate-bearing sediments. Having the above fundamental insights, the geophysical and geothermal responses of hydrate-free and hydrate-bearing sediments were characterised by measuring their elastic wave velocities and effective thermal conductivity (ETC) at different hydrate saturations (up to 55%) and effective overburden pressures (up to 6.89 MPa) at both unfrozen and frozen conditions. The results confirmed that the evolution of the elastic wave velocities as well as ETC depends on the saturation and pore-scale habit of hydrates; and ETC could interestingly assist with distinguishing ice from hydrates. The ETC measurements also revealed that the presence of hydrates in porous media is associated with three key pore-scale phenomena contributing to the efficiency of the heat transfer: the saturation and pore-scale habit of hydrates, hydrate/ice-forced heave, and unfrozen water saturation at frozen conditions. Moreover, a new physical model was developed for the prediction of ETC of hydrate-free sediments using the Free-energy Lattice Boltzmann Model (LBM) and a space renormalisation technique, and modified according to the insights from the ETC measurements to account for the effect of the above-mentioned key pore-scale phenomena. Ultimately, the coupled geophysical-geothermal scheme was developed by using the modified ETC model as the geothermal part and Ecker’s rock-physics models as the geophysical part, and its performance was validated using the measured geophysical and geothermal properties. It was demonstrated that the proposed coupled scheme is able to quantify the saturation of the co-existing phases in a wide range of hydrate saturations and at different effective overburden pressures, particularly at frozen conditions where the co-existence of hydrates, ice, and unfrozen water is essential to be captured. This scheme makes it possible to distinguish ice from gas hydrates in frozen sediments hence it could be employed for not only quantification of gas hydrates in permafrost but also further development of large-scale permafrost monitoring systems for monitoring the dynamic response of gas hydrate-bearing permafrost sediments to climate warming in cold regions.James Watt Scholarshi

Functionalism in Translation: A Case Study Investigation into Translation literature based on Nord's Documentary vs. Instrumental Dichotomy

The main objective of the current study was to analyze a Persian Translation of a short story from functionalism perspective and Documentary vs. Instrumental Dichotomy. To this end, the Persian translation of the book titled “The Little Prince” was analyzed and compared with its English version (indirect translation from French) to see if the Persian translation was more documentary or instrumental oriented in nature. The theoretical framework of the study was Nord’s dichotomy of instrumental vs. documentary translation. The book was analyzed at the sentence and above sentence level and covered the whole book. As the qualitative analysis showed, the translation of the book was instrumental oriented, and the book reads like an original in the target language

Metadiscourse in Academic Written and Spoken English: A Comparative Corpus-Based Inquiry

This paper reports on a comparative study performed in the field of Corpus Linguistics. The objective of the research was to analyze the distributional pattern of interactive and interactional metadiscourse features in two modes of academic spoken and written English. For this reason, a list of metadiscourse characteristics was gathered. By using the Sketch engine software, all the words were scrutinized in the corpus and their concordance lines were analyzed one by one in both corpora (British Academic Written English Corpus and British Academic Spoken English Corpus). As the data can show, in both corpora, the general propensity of the authors was towards the interactive metadiscourse features. In addition, in the written corpus, the transitions and endophoric markers were used more often; while in the spoken, endophoric markers and transitions were the most frequently applied metadiscourse features. In the interactional metadiscourse features, hedges and self-mentions were the most frequent in the written form; whereas in the spoken, self-mentions and boosters were used moe often

Insights into the climate-driven evolution of gas hydrate-bearing permafrost sediments: implications for prediction of environmental impacts and security of energy in cold regions

The present study investigates the evolution of gas hydrate-bearing permafrost sediments against the environmental temperature change. The elastic wave velocities and effective thermal conductivity (ETC) of simulated gas hydrate-bearing sediment samples were measured at a typical range of temperature in permafrost and wide range of hydrate saturation. The experimental results reveal the influence of several complex and interdependent pore-scale factors on the elastic wave velocities and ETC. It was observed that the geophysical and geothermal properties of the system are essentially governed by the thermal state, saturation and more significantly, pore-scale distribution of the co-existing phases. In particular, unfrozen water content substantially controls the heat transfer at sub-zero temperatures close to the freezing point. A conceptual pore-scale model was also proposed to describe the pore-scale distribution of each phase in a typical gas hydrate-bearing permafrost sediment. This study underpins necessity of distinguishing ice from gas hydrates in frozen sediments, and its outcome is essential to be considered not only for development of large-scale permafrost monitoring systems, bus also accurate quantification of natural gas hydrate as a potential sustainable energy resource in cold regions

On the effect of flow regime and pore structure on the flow signatures in porous media

In this study, lattice Boltzmann method (LBM) is utilized for three-dimensional simulation of fluid flow through two porous structures, consisting of grains with the same diameter: (i) a homogeneous porous domain, in which the grains are placed with a simple cubic packing configuration, and (ii) a randomly packed porous domain. An ultra-fine mesh size is considered to perform the simulations in three orders of magnitude of Reynolds number (Re), covering laminar to turbulent flow regimes, and capture different flow signatures. Pore velocity fields are derived, and their sample probability density functions (PDF) are analyzed vs time to investigate the dynamics of the flow. The analysis of the PDFs clearly shows that stagnant zones play a significant role in the formation of the pore flow fields, manifested by multimodal PDFs, and the distribution of the velocities in porous media at various Re cannot be characterized by a single PDF model regardless of the pore structure. While the velocities at the stagnant regions and in the vicinity of the solid boundaries are primarily affected by the viscous forces and exhibit a power-law PDF at different Re, the velocities in the main (preferential) flow pathways away from the boundaries are shown to be influenced by the inertial forces, hence having an exponential PDF when Re is low. At high Re, however, depending on the tortuosity of the porous structure, the velocities may exhibit an exponential or even Laplace PDF

Gas hydrates in sustainable chemistry

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hassanpouryouzband, A., Joonaki, E., Farahani, M. V., Takeya, S., Ruppel, C., Yang, J., English, N. J., Schicks, J. M., Edlmann, K., Mehrabian, H., Aman, Z. M., & Tohidi, B. Gas hydrates in sustainable chemistry. Chemical Society Reviews, 49(15), (2020): 5225-5309, doi:10.1039/c8cs00989a.Gas hydrates have received considerable attention due to their important role in flow assurance for the oil and gas industry, their extensive natural occurrence on Earth and extraterrestrial planets, and their significant applications in sustainable technologies including but not limited to gas and energy storage, gas separation, and water desalination. Given not only their inherent structural flexibility depending on the type of guest gas molecules and formation conditions, but also the synthetic effects of a wide range of chemical additives on their properties, these variabilities could be exploited to optimise the role of gas hydrates. This includes increasing their industrial applications, understanding and utilising their role in Nature, identifying potential methods for safely extracting natural gases stored in naturally occurring hydrates within the Earth, and for developing green technologies. This review summarizes the different properties of gas hydrates as well as their formation and dissociation kinetics and then reviews the fast-growing literature reporting their role and applications in the aforementioned fields, mainly concentrating on advances during the last decade. Challenges, limitations, and future perspectives of each field are briefly discussed. The overall objective of this review is to provide readers with an extensive overview of gas hydrates that we hope will stimulate further work on this riveting field.A. H. and K. E. were partially supported by funding from UKRI-EPSRC (grant number EP/S027815/1). C. R. was partially supported by DOE-USGS Interagency agreement DE-FE0023495. C. R. thanks L. Stern and W. Waite for insights that improved her contributions. E. J. is partially supported by Flow Programme project sponsored by Department for Business, Energy and Industrial Strategy (BEIS), UK. Any use of trade, firm or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government