Investigation of asphaltene-derived formation damage and nano-confinement on the performance of CO2 huff-n-puff in shale oil reservoirs

In this study, the behavior of asphaltene formation and nano-confinement during the CO2 huff-n-puff process in liquid-rich shale reservoirs is investigated. Asphaltene precipitation and deposition in the pore volume of shale formation from mixing between oil and CO2 could cause formation damage, which reduces the permeability and/or changes the rock surface condition toward more oil-wet. In addition, the nano-confinement effect changes the phase behavior of the fluid affecting the asphaltene formation in tight shale formations. With the development of a reservoir simulation model that incorporates both asphaltene formation and the nano-confinement effect, this study quantifies the effects of asphaltene deposition and nano-confinement on shale oil production of CO2 huff-n-puff. While ignoring the permeability reduction and wettability alteration due to asphaltene deposition, the nano-confinement effect increases the shale oil production by up to 42% during the CO2 huff-n-puff process. However, the nano-confinement effect increases the asphaltene precipitation and deposition in nano-scaled tight formation. On incorporating the formation damage due to asphaltene deposition, more deposited asphaltene due to nano-confinement effect decreases the oil production by 4%. This study clarifies that the effects of asphaltene formation and nano-confinement should be taken into consideration for an accurate prediction of hydrocarbon production during CO2 huff-n-puff in tight shale formation.