Investigation into the Methane Displacement Behavior by Cyclic, Pure Carbon Dioxide Injection in Dry, Powdered, Bituminous Indian Coals

摘要

Understanding competitive sorption effects for the carbon dioxide-methane system in coal is essential for the implementation of enhanced methane production with concomitant CO_2 sequestration in coal. The paper discusses the methane displacement behavior of a set of eight dry, powdered Indian bituminous coal samples when subjected to cyclic, pure CO_2 injection, employing a "huff and puff" scheme. The coal samples were partially saturated with methane, and CO_2 was then injected at a fixed pressure. This was followed by gas drainage to reduce pressure to the pre-injection level, and about 12-15 such cycles of CO_2 injection and gas drainage were carried out In general, the process successfully displaced die adsorbed methane. The adsorption ratio of CO_2/methane was found to be higher than pure gas sorption capacities at the same pressure. Carbon dioxide was preferentially adsorbed into the coals, and during gas drainage, preferential desorption of methane was observed for all coals. The coals also exhibited different methane displacement behavior. For three coal samples, it was possible to recover 1 mol of methane by injecting less than 1 mol of CO_2. For the other coal samples, 1.5-2 mol of CO_2 was required for 1 mol of methane. However, no relationship could be established between the methane release characteristics of the coals and their petrographic composition.