Insights into the Control Mechanism of Heat Transfer on Methane Hydrate Dissociation via Depressurization and Wellbore Heating

Abstract

The dissociation of natural gas hydrate is an endothermic reaction controlled by heat transfer, which is closely associated with the employed exploitation methods and well configurations. The main purpose of this study is to investigate the relationship between heat transfer and gas hydrate dissociation in a cuboid pressure vessel with different vertical well layouts (central well and side well) and production methods (pure depressurization (PD), depressurization combined with wellbore heating (DH), and huff and puff (HP)) through experimental and numerical simulations. The results show that the hydrate dissociation in the PD cases is promoted only by heat conduction from the surrounding environment. The heat transfer behaviors are basically the same when adopting depressurization with different wellbore locations. Addition of wellbore heating in the DH and HP cases will result in faster hydrate decomposition. However, heat conduction from the ambient will be impeded by wellbore heating. The cumulative heat transferred across the boundary will drop below 0 at a certain time, which would subsequently lead to a sharp rise of the heat loss. To reduce heat loss across the boundary, the heating section of the wellbore should be placed in the central area of the hydrate-bearing layer. In addition, it is found that intermittent heat injection with the HP method has the advantages of enhancing the heat convection effect and reducing the heat absorption of the hydrate deposit, which results in more favorable heat utilization efficiency and net energy gain.

Numerical Investigation into the Gas Production from Hydrate Deposit under Various Thermal Stimulation Modes in a Multi-Well System in Qilian Mountain

“…As the geographical conditions are characterized by low temperature, pure depressurization will be accompanied by a low recovery rate of natural gas due to the finite sensible heat stored in the underground deposit [ 21 ]. Many studies [ 15 , 16 , 23 ] came to a similar conclusion that the depressurization-induced gas production could be significantly improved if sufficient external heat is provided to overcome the problem of energy shortage. However, the adoption of pure thermal stimulation will also perform unfavorably if no other strategies are combined with it for hydrate decomposition.…”

“…Subsequent studies indicate that desirable gas-to-water ratio and energy efficiency can be obtained under suitable injection and production conditions with the huff and puff method. This is because the huff and puff method has the advantages of enhancing the heat convection effect and reducing the heat absorption of the hydrate deposit [ 22 , 23 ]. To provide insightful guidance for field-scale exploitation of gas hydrate, people have employed various numerical codes to simulate the production potentials of various hydrate deposits.…”

Thermal Diffusion Characteristics in Permafrost during the Exploitation of Gas Hydrate

“…From the field experience of Canada, Russia, and US hydrate production in the permafrost region ( Figure 1) [9,11,12,26], the hydrate production operation will change the temperature of reservoir skeleton (rock, ice, and hydrate). This temperature change will dramatically affect the efficiency of hydrate production [27,28]. It may conduct the wellbore instability, sand production ( Figure 2), and methane leakage [26,[29][30][31].…”

Experimental and Modeling Study of Kinetics for Hydrate Decomposition Induced by Depressurization in a Porous Medium

“…Compared with the productions of other conventional fossil fuels, the methane gas production from hydrate reservoir should make hydrate in situ dissociation and ensure the safety and stability of reservoir. Generally, the hydrate dissociation in porous media is controlled by dissociation reaction kinetics (Kim et al, 1987;Hong et al, 2003;Tang et al, 2007;Yin et al, 2020), heat and mass transfer (Selim and Sloan, 1989;Tonnet and Herri, 2009;Konno et al, 2014;Chen et al, 2017;Wan et al, 2020;Yin et al, 2020;Li et al, 2021), and fluid flow (Yousif et al, 1990;Moridis, 2004;Tang et al, 2007;Kumar et al, 2010;Yu et al, 2021). It is considered that different control mechanisms are coupling, and any of the abovementioned mechanisms (mechanisms discussed above) could be the dominating factor in the gas production process according to the scale and properties of hydrate-bearing sediments (Tang et al, 2007;Tonnet and Herri, 2009;Kumar et al, 2013;Wang Y.-F. et al, 2020;.…”