Carbon dioxide emission into the atmosphere is considered as the cause of global warming and geologic storage of carbon dioxide is one of the most effective and safe way to reduce carbon dioxide concentration. There are several types of formation for geologic storage of carbon dioxide and coal beds receive attention due to its high efficiency of storage and additional production of methane which can reduce the implementation cost of geologic storage of carbon dioxide. In this study, a series of numerical simulations using a multi-dimensional thermo-hydrogeological-chemical numerical model is performed to analyze migration and adsorption of fluids (carbon dioxide, methane, and groundwater) and to estimate the influences of the cleat spacing and the formation dip on them due to geologic storage of carbon dioxide in coal beds. A conceptual model of simulation is based on Samcheock coal field which is the largest coal field in Korea to consider features of domestic coal field.
The results of the numerical simulations show that fluids flow in the coal cleat is impacted by the variation of cleat spacing and formation dip. The results of a series of numerical simulations show that up to the 88% of carbon dioxide are adsorbed in the matrix regardless of variation of cleat spacing or formation dip. And most of injected carbon dioxide migrates and are adsorbed to the top boundary of coal beds. Methane and groundwater are pushed to the outside from injection well by carbon dioxide, and some methane is adsorbed again in the carbon dioxide adsorbed area. The results of sensitive analysis of cleat spacing show that spatial distribution of carbon dioxide, methane and groundwater are impacted by change of cleat spacing. According to decreasing of cleat spacing, the more carbon dioxide and methane flows up to the boundary of coal beds, and the influenced areas of carbon dioxide increase. Results of sensitive analysis of formation dip show that flows of fluids are significantly affected by formation dip. Carbon dioxide and methane flow rapidly in the direction toward surface. Velocities of carbon dioxide and methane flow are drastically increased according to increasing of formation dip. As a result, some methane and carbon dioxide moves out of the domain.
Results of this study show that a multi-dimensional thermo-hydrogeological-chemical numerical model is useful to predict complex migration and adsorption mechanism of fluids due to geologic storage of carbon dioxide. And results of this study are expected to contribute to establish reasonable and effective plan of geologic storage of carbon dioxide.