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OS6B-5:AN INVESTIGATION OF THE INFLUENCE OF N2 SWEEP ON METHANE RECOVERY FROM HYDRATE DEPOSITS
发布时间:2014-07-28
Xiaohui WANG, Changyu SUN , Yanan HE, Yifei SUN, Nan LI, Guangjin CHEN
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, CHINA
The replacement of CH4 hydrate with CO2 recently has been suggested as an alternative option for recovering CH4 from seafloor gas hydrate deposits. The direct use of gas mixture (N2+CO2) instead of pure CO2 can greatly enhance the overall CH4 recovery ratio. In the actual hydrate exploitation, the replacement process through injecting large amounts of gas mixture may be accompanied with depressurization and thermal stimulation. To evaluate the influence of gas sweep on methane recovery, pure N2 was injected into hydrate-bearing sediments. This experiment was carried out in a scale-up three-dimensional apparatus with volume of 7L, and simultaneously contrasted the difference of the interval injection mode and the continual injection mode. The influence factors, including hydrate saturation, N2 injection rate, the total amount of N2 and initial production pressure were investigated. The experimental results indicate that the gas sweep process is mainly a depressurization process and the methane recovery rate by pure N2 injection is much quicker than CO2 replacement and direct depressurization. With the decreasing of initial production pressure, the hydrate dissociation rate increases, causing the temperature of hydrate sediments decreases rapidly and reaches the phase equilibrium condition. Compared with the interval injection mode, the continual injection mode needs more N2 to fully recover methane from hydrate-bearing sediments. According to the experimental results, the injection of gas indeed can cause hydrate decompose and improve methane recovery ratio. Therefore, when evaluating the recovery efficiency of gas mixture（N2+CO2）replacement method, it is important to distinguish the contribution of depressurization caused by gas sweep with replacement in future research.
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, CHINA
The replacement of CH4 hydrate with CO2 recently has been suggested as an alternative option for recovering CH4 from seafloor gas hydrate deposits. The direct use of gas mixture (N2+CO2) instead of pure CO2 can greatly enhance the overall CH4 recovery ratio. In the actual hydrate exploitation, the replacement process through injecting large amounts of gas mixture may be accompanied with depressurization and thermal stimulation. To evaluate the influence of gas sweep on methane recovery, pure N2 was injected into hydrate-bearing sediments. This experiment was carried out in a scale-up three-dimensional apparatus with volume of 7L, and simultaneously contrasted the difference of the interval injection mode and the continual injection mode. The influence factors, including hydrate saturation, N2 injection rate, the total amount of N2 and initial production pressure were investigated. The experimental results indicate that the gas sweep process is mainly a depressurization process and the methane recovery rate by pure N2 injection is much quicker than CO2 replacement and direct depressurization. With the decreasing of initial production pressure, the hydrate dissociation rate increases, causing the temperature of hydrate sediments decreases rapidly and reaches the phase equilibrium condition. Compared with the interval injection mode, the continual injection mode needs more N2 to fully recover methane from hydrate-bearing sediments. According to the experimental results, the injection of gas indeed can cause hydrate decompose and improve methane recovery ratio. Therefore, when evaluating the recovery efficiency of gas mixture（N2+CO2）replacement method, it is important to distinguish the contribution of depressurization caused by gas sweep with replacement in future research.
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