Energy & Fuels, Vol.34, No.5, 5689-5695, 2020
Adsorption Behavior of CH4 and C2H6 on Shale under the Influence of CO2 and Flue Gas
CO2 injection has been accepted as a suitable method for enhancing shale hydrocarbon recovery as well as achieving CO2 storage in shale reservoirs. In this study, flue gas is proposed as a better injection gas for shale resource recovery. The objective of this work is conducted to investigate how introduced CO2 and flue gas affect the adsorption behavior of CH4 and C2H6, which are two main components in shale gas, on shale, which is critical for understanding the fundamental mechanism of shale gas recovery. In this work, the adsorption isotherms are first measured to evaluate the relative adsorption capacity of CO2, flue gas, CH4, and C2H6 on typical shale samples. The low-field nuclear magnetic resonance technique is consequently applied to study the influence of injected CO2 and flue gas on the adsorption behavior of CH4 and C2H6 at the reservoir pressure and temperature conditions. Test results show that flue gas presents the highest adsorption capacity on shale, which is followed by C2H6, CO2 and CH4, respectively. On the basis of the measured T-2 signals, CH4 and C2H6 exist in shale within the two patterns, i.e., the adsorbed pattern in pores and the free-state pattern at the pore center. After injection of CO2 and flue gas, the amount of adsorbed CH4 is reduced, accompanying with the increase of the quantity of free gas state that appeared at the pore center. In comparison to CO2 flue gas can further replace adsorbed CH4 and C2H6 from the shale surface, suggesting more feasibility of flue gas for enhancing CH4 and C2H6 recovery. This study may inspire new strategies that can be applied for shale reservoir development; more importantly, it may provide a new way for the usage of flue gas for energy supply while reducing the possibility for environmental pollution.