Adsorption-induced pore blocking and its mechanisms in nanoporous shale due to interactions with supercritical CO2

Abstract

Supercritical carbon dioxide (sCO2) has recently been used to recover hydrocarbons from shale formations due to its advantages in boosting production, saving water, and minimizing environmental impacts. Meanwhile, CO2 is sealed up underground, which would cut down the greenhouse gas emissions and reduce global warming. However, current knowledge regarding how sCO2 interacts with shale, especially its nanopores which are responsible for adsorption, migration and storage of oil and gas, has been lacking. Here we show that after sCO2 adsorption, the total pore volume decreases by ∼20% in nanoporous shale, majorly by up to 60% in the range of 0.85–2.0 nm. We analyze the morphology and composition changes in shale, and show that the nanopore is either closed up or newly opened, with more closed pores than new ones. We for the first time propose that this adsorption-induced pore blocking phenomenon is jointly voluminal and geochemical resulted from physisorption, associative chemisorption and dissociative chemisorption of sCO2 in shale. Our results help to effectively assess the hydrocarbon production capacity in shale gas reservoirs using CO2-fracking technique, and the CO2 storage potential in shale formations.