Abstract
Natural gas hydrate (NGH) is a potential type of clean and efficient energy that is widely distributed in the ocean and permafrost, and most of the present researches are mainly focused on finding out efficient exploitation methods. Taking the effects of natural gas productivity and extraction time into account, one of the exploitation methods that are most commonly investigated is depressurization combined with thermal stimulation. However, few studies considered the effect of different mining methods on NGH production in vertical wells, especially aiming at the in-situ electric heating without mass injection and the comparison of production efficiency in different modes. Considering the current research status, four exploitation methods which are pure depressurization (PD), pure heating (PH), simultaneous depressurization combined with electric heating (SDH) and huff and puff (H&P) were carried out in this paper to study the influences of different production methods on NGH exploitation in a vertical well. Some parameters such as gas production (VP), water production (CP) and the energy efficiency (η) were investigated to evaluate the production performance of these methods. The results suggest that the temperature in the reactor is affected by the exploitation methods as well as the water production during exploitation. For PD, although it has no extra energy consumption, the longest production period is seen in it due to the insufficient pressure driving force. On the contrary, the NGH cannot be completely exploited only triggered by heating driving force with PH method. So there is a limited decomposition effect with it. Taking the gas production time, the VP, and the NGH dissociation rate into account, the production effects of SDH are more beneficial than other methods as the dual decomposition driving force was adopted in it. Furthermore, a reasonable heating power can result in a better production performance. On the other hand, promoted by pressure difference and discontinuous heating, H&P shows its obvious advantage in shortening production duration and improving energy efficiency, which is therefore believed to have the best commercial exploitation value among the four methods.
Highlights
Natural gas hydrate (NGH) is a kind of crystal compound that is mainly formed by water molecules binding methane molecules under the condition of low temperature and high pressure [1].The hydrate-forming gas molecules (e.g., CH4, C2 H6 and CO2 ) are usually small and light, and the Energies 2019, 12, 124; doi:10.3390/en12010124 www.mdpi.com/journal/energiesEnergies 2019, 12, 124 hydrate is found to have three types of structures in nature (i.e., Type I, II and H) [2,3]
It could be seen that the temperatures at different locations of the reactor increased gradually, meaning that the heat originated from electric heating could be efficiently transferred from the heating well to the hydrate sediment
This was because T1 and T9 were located in the corners of the reactor, the hydrate around which could absorb heat from two adjacent boundaries of the reactor
Summary
Natural gas hydrate (NGH) is a kind of crystal compound that is mainly formed by water molecules binding methane molecules under the condition of low temperature and high pressure [1].The hydrate-forming gas molecules (e.g., CH4 , C2 H6 and CO2 ) are usually small and light, and the Energies 2019, 12, 124; doi:10.3390/en12010124 www.mdpi.com/journal/energiesEnergies 2019, 12, 124 hydrate is found to have three types of structures in nature (i.e., Type I, II and H) [2,3]. Natural gas hydrate (NGH) is a kind of crystal compound that is mainly formed by water molecules binding methane molecules under the condition of low temperature and high pressure [1]. Formation and dissociation processes of NGH can be expressed by the reversible reaction equation below [4,5,6]: CH4 + n H H2 O ↔ CH4 ·n H H2 O + ∆Hen (1). The occurrence of gas hydrate is strongly dependent on the factors including temperature, pressure and constituent components, which result in the formation of NGH in polar and oceanic regions [7,8,9]. It is deposited in the natural slope under cold water along the bottom of the continental margin. NGH has been found to be contained in about 95%
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
