Adsorption/Desorption Behavior of CH4 on Shale during the CO2 Huff-and-Puff Process

Abstract

The CO2 huff-and-puff method has been widely adopted for enhancing CH4 recovery in shale reservoirs. Revealing the behavior of CH4 adsorption/desorption in shale during the CO2 huff-and-puff process clarifies the recovery mechanisms of CH4 from shale reservoirs. In our work, the question of how CO2 plays a role in affecting the adsorption/desorption of CH4 is investigated using the low-field nuclear magnetic resonance technique. In addition, phase transition of CH4 is also analyzed to investigate how the existing states of CH4 transform in shale during this process. Specifically, the states in which CH4 resides in shale are first recognized by analyzing the measured T2 spectrum of shale after injecting CH4. CO2 huff-and-puff tests are then conducted to investigate how CO2 impacts the adsorption/desorption behavior of CH4 on shale samples. Furthermore, the T2 signals of shale during depressurization are measured to investigate the state transformation of CH4 in shale during the CO2 huff-and-puff process. T...