科研之友
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摘要
Recently, exhaustion of primary energy sources and increase in the atmospheric CO2 levels have become two major energy challenges of the world; therefore, utilization of alternative energy sources and avoiding the emission of greenhouse gases to the atmosphere are some of the serious problems of this century that should be addressed immediately. Many alternatives are being assessed to solve or at least to cease the negative effects of these issues. %26lt;br%26gt;Vast amount of methane in the form of gas hydrates is stored in several deep marine sediments and in permafrost region. Therefore, production of methane from hydrates may postpone the former problem for significant period of time. Although several production mechanisms like depressurization, thermal treatment and inhibitor injection have been proposed, recovery of methane from hydrate bearing sediments is still an issue of debate. Also, it is widely believed that CO2 emissions due to fossil fuel combustion and transportation are mainly responsible for the increase in the global temperature level. Therefore, several options are being evaluated to diminish the anthropogenic CO2 emissions like storing the captured CO2 in another domain of the planet for example, the geosphere. At this point, the injection of CO2 into CH4 hydrate bearing sediments deserves particular attention as this technique may enable integration of CO2 storage with production from CH4 hydrates. %26lt;br%26gt;In this study, gaseous CO2 was injected into the unconsolidated sand pack system which includes 30% methane hydrate saturation at free CH4 excess conditions. After the CO2 injection, cyclic behaviors at the pressure gauges were observed for approximately 6 h that may indicate CH4-CO2 swap within hydrate cages. It was thought that the cyclic behaviors in the pressure gauges indicate CO2-CH4 swap within the hydrate cages. Upward and downward trends in cycles results from the gaseous CH4 that was leaving the cages and gaseous CO2 that was stabilizing the cages respectively. Swap process was confirmed by estimating the gas compositions at the instant of CO2 injection and by measuring via gas chromatography analyses after the swap process. As a result of the swap process, it was estimated that 86.3% of the CO2 filled the hydrate cages. After stabilization, system was left to dissociate for several days and samples taken from the cell at different time intervals were analyzed via gas chromatography in order to gain an insight on hydrate distribution in porous media after the swap process. Analyses showed that, amount of free CO2 in the cell were increasing gradually reached a peak value and then decreased. This suggests that, CH4-CO2 swap process mostly took place at the surface of the system as the injected CO2 initially accumulated at the external part of the unconsolidated sand pack system and the area where the reaction took place was maximum. The results obtained from this research proposed that the injection of gaseous CO2 causes dissociation of methane hydrate also samples that were taken during the dissociation process may give some insight about the probable hydrate distribution at the system.
- 出版日期2014-7
