Our previous coreflood experiments - injecting pure CO2 into carbonate cores - showed that the process is a win-win technology, sequestrating CO2 while recovering a significant amount of hitherto unrecoverable natural gas that could help defray the cost of CO2 sequestration. In this paper, we report our findings on the effect of "impurities" in flue gas - N2, O2, H2O, SO2, NO2, and CO - on the displacement of natural gas during CO2 sequestration. Coreflood experiments were conducted at 1,500 psig and 70°C, in which a flue gas was injected into a carbonate core containing initially methane. Two types of flue gas were injected: dehydrated flue gas with 13.574 mole % CO2 (Gas A), and treated flue gas (N2, O2 and water removed) with 99.433 mole % CO2 (Gas B).

Main results of our study to-date are as follows. First, during displacement of methane, the dispersion coefficient increases with concentration of the "impurities". Gas A exhibits the largest dispersion coefficients, 0.18 - 0.25 cm2/min, compared to 0.13 - 0.15 cm2/min for Gas B, and 0.15 cm2/min for pure CO2. Second, for all cases, recovery of methane at breakthrough is relatively high, ranging from 86% OGIP for pure CO2, 74-90% OGIP for Gas B, and 79-81% for Gas A. Lastly, injection of Gas A would sequester the least amount of CO2 as it contains about 80 mole % nitrogen. From the view point of sequestration, Gas A would be least desirable (though the cheapest separation process). Gas B (flue gas with N2, O2 and water removed) appears to be the most desirable as separation cost would probably be cheaper than that for pure CO2 while natural gas recovery are similar in both cases.

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