Influence of gas sweep on methane recovery from hydrate-bearing sediments

Kuang

et al. 2017

Ind. Eng. Chem. Res.

The application of air or nitrogen injection to extract natural gas from hydrates has attracted considerable attention because air and nitrogen are abundant; however, few studies have considered the relatively new method. This study employed magnetic resonance imaging to investigate the characteristics of hydrate dissociation via N2 injection. The results show that methane hydrate dissociation using N2 injection can be divided into three main stages: free gas and water liberation, hydrate dissociation driven by chemical potential differences, and restriction of hydrate dissociation due to increased resistance to N2 diffusion and a decreased contact area between N2 and hydrate. Various factors associated with the N2 injection method were considered, including injection rate and hydrate saturation. Furthermore, a comparison of recovery:injection ratio and methane cumulative production ratio to the results of hydrate dissociation via depressurization suggests that during low-hydrate saturation exploitation, N2 injection has advantages over the depressurization method.

Section: Resultsmentioning

confidence: 88%

Section: Industrial and Engineering Chemistry Researchmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Analyzing the Process of Gas Production from Methane Hydrate via Nitrogen Injection

Kuang

et al. 2017

Ind. Eng. Chem. Res.

“…Therefore, the heat released by 0.375 mol NaNO 2 and NH 4 Cl can decompose 0.96∼1.01 mol NGHs at the low temperature of 4 C. From the perspective of thermal decomposition, the thermochemical reaction system in this study is feasible in exploiting the of NGH reservoir. Moreover, a novel concept of injecting air or gaseous N 2 into NGHs has been proposed recently (Panter et al, 2011;Wang et al, 2015;Zhang et al, 2017b;Okwananke et al, 2018). As N 2 is injected at the gaseous state, it can readily be dispersed in plugged pipelines or NGH-saturated layers with high permeability.…”

Section: Discussionmentioning

confidence: 99%

A Thermal Chemical Reaction System for Natural Gas Hydrates Exploitation

Wang

Sun

et al. 2022

Front. Energy Res.

The methodology of using CO2 to replace CH4 to recover the natural gas hydrates (NGHs) is supposed to avoid geological disasters. However, the reaction path of the CH4–CO2 replacement method is too complex to give satisfactory replacement efficiency. Therefore, this study proposed a thermochemical reaction system that used the heat and the nitrogen released by the thermochemical reactions to recover NGHs. The performance of the thermochemical reaction system (NaNO2 and NH4Cl) regarding heat generation and gas production under low temperature (4°C) conditions was evaluated, and the feasibility of exploiting NGHs with an optimized formula of the thermochemical reaction system was also evaluated in this study. First, the effects of three catalysts (HCl, H₃PO₄, and NH2SO3H) were investigated at the same reactant concentration and catalyst concentration. It was confirmed that HCl as a catalyst can obtain better heat generation and gas production. Second, the effect of HCl concentration on the reaction was investigated under the same reactant concentration. The results showed that the higher the HCl concentration, the faster is the reaction rate. When the concentration of HCl was greater than 14 wt%, side reactions would occur to produce toxic gas; hence, 14 wt% was the optimal catalyst concentration for the reaction of NaNO2 and NH4Cl at low temperatures. Third, the heat generation and gas production of the thermochemical reaction systems were evaluated at different reactant concentrations (1, 2, 3, 4, 5, and 6 mol/L) at 14 wt% HCl concentration. It was found that the best reactant concentration was 5 mol/L. Finally, the feasibility of exploiting NGHs with the optimal system was analyzed from the perspectives of thermal decomposition and nitrogen replacement. The thermochemical reaction system provided by this study is possible to be applied to explore NGHs’ offshore.

“…Pure CO 2 is not suitable for the CH 4 –CO 2 exchange in MH. Direct injection of CO 2 would result in rapid CO 2 hydrate formation at the injection point and substantial loss of injectivity. , Therefore, N 2 is considered to be a suitable additive to prevent CO 2 hydrate formation and effectively enhances CH 4 recovery during the CH 4 –CO 2 replacement process. ,,− Park et al first pointed out that CH 4 recovery can be increased using N 2 and CO 2 , presumably because the N 2 molecules can easily drive out CH 4 from the small cages. Discussions of kinetics on CH 4 –CO 2 or CH 4 –(N 2 + CO 2 ) gas exchange can be described as follows: the gas exchange is observed as two-stage replacement initiated by almost instantaneous formation of a mixed hydrate layer on the hydrate surface, followed by a much slower diffusion-controlled process. ,,,− The mixed hydrate layer consists of CH 4 , CO 2 , and/or N 2 hydrate.…”

Section: Introductionmentioning

confidence: 99%

Estimation of Methane Recovery Efficiency from Methane Hydrate by the N₂–CO₂ Gas Mixture Injection Method

2020

Methane hydrate (MH) is the best-known unconventional energy resource and has begun to open its promising future, especially for Japan. In 2017, the second offshore gas hydrate field test was conducted in the Eastern Nankai Trough, Japan, where a depressurization technique was adopted for producing methane gas. Alongside the depressurization method, the replacement of CH4 from gas hydrates by a N2–CO2 gas mixture was suggested and adopted to increase performance for both methane gas recovery and carbon dioxide sequestration. The amount of abundant MHs is estimated to exist in the permafrost area; therefore, this method, which does not require any heat source, can be used as a standard method for recovering methane. In this study, experiments to continuously inject a N2–CO2 gas mixture (59 mol % CO2) into hydrate-bearing cores with different MH saturations were conducted. Simultaneously, the numerical simulation model was constructed, and to express the gas exchange phenomenon of CH4–(N2 + CO2), the phase equilibrium analyses were used between the gas mixture and hydrates. Good agreements were obtained between experiments and simulations. At these experiments, the recovery factor of 40.8% and the exchange ratio of 8.22% were recorded as an example. The validation of the simulation with experimental results strongly supported our study to find the efficient injection gas composition for methane recovery. Case studies of the numerical simulation were conducted with various CO2 concentrations of injection gas in the range of 24–72 mol %. Simulation results showed that the highest recovery factor was obtained for the 30–40 mol % CO2 gas injection cases. The higher the N2 concentration of the gas mixture, the more CH4 molecules in the hydrate phase can be replaced. In the gas exchange process, the portion of N2 occupied in guest gas molecules of the hydrate became larger with increasing the N2 concentration of the gas mixture. From the discussion above, we concluded that the CO2 concentration of 30–40 mol % was the most effective for CH4 recovery by the N2–CO2 gas mixture injection method.