Comparison and Optimization of Methane Hydrate Production Process Using Different Methods in a Single Vertical Well

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.

Numerical Simulations of Combined Brine Flooding With Electrical Heating–Assisted Depressurization for Exploitation of Natural Gas Hydrate in the Shenhu Area of the South China Sea

“…To overcome the shortcoming of traditional hot water/steam flooding method, novel thermal stimulation methods of electrical or electromagnetic heating and methane in situ combustion have been proposed, which generate heat directly in the formation to avoid wellbore heat loss. In this study, we focus on electrical heating, and many laboratory experiments have been conducted to clarify the effects of electrical heating-assisted depressurization on hydrate dissociation and methane recovery (Falser et al, 2012;Li et al, 2018a;Liang et al, 2018;Minagawa et al, 2018;Wan et al, 2020a;Wan et al, 2020b;He et al, 2021). For example, Li et al (2018b) found that the production efficiency of depressurization can be greatly enhanced by using the electrical heating simultaneously for the methane hydrate in a cuboid pressure vessel.…”

Research on the Influence of Injection–Production Parameters on Challenging Natural Gas Hydrate Exploitation Using Depressurization Combined with Thermal Injection Stimulated by Hydraulic Fracturing

“…This method can also significantly improve the energy ratio compared with the thermal stimulation method alone. Current studies determined that depressurisation combined with hot water injection (D + T iw ) significantly increased the NGH decomposition rate and CH 4 production rate. ,− However, in a low-permeability NGH reservoir, the poor depressurisation effect and hot water flow capacity severely limit the production capacity of D + T iw. , …”

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

“…To solve the problem of insufficient heat supply by depressurization, the thermal stimulation method has attracted people’s attention . It is realized by providing extraneous heat to raise the reservoir temperature above the equilibrium temperature . Heat can be supplied to the hydrate deposit in the form of hot water injection, steam stimulation, electrical heating, in situ catalytic oxidation of CH 4 , etc.…”

“…17 It is realized by providing extraneous heat to raise the reservoir temperature above the equilibrium temperature. 18 Heat can be supplied to the hydrate deposit in the form of hot water injection, 19 steam stimulation, 20 electrical heating, 21 The hydrate dissociation rate can be enhanced prominently due to faster heat transfer from the injection point to the hydrate regions. 23 This method is usually combined with depressurization to optimize the exploitation process.…”