Review of CO2-kerogen interaction and its effects on enhanced oil recovery and carbon sequestration in shale oil reservoirs

Shale oil resources have proven to be quickly producible in large quantities and have recently revolutionized the oil and gas industry. The oil content in a shale oil formation includes free oil contained in pores and trapped oil in the organic material called kerogen. The latter can represent a significant portion of the total oil and yet production of shale oil currently targets only the free oil rather than the trapped oil in kerogen. Shale oil reservoirs also have a substantial capacity to store CO2 by dissolving it in kerogen. In this paper, recent progress in the research of CO2-kerogen interaction and its applications in CO2 enhanced oil recovery and carbon sequestration in shale oil reservoirs are reviewed. The relevant topics reviewed for this relatively new area include characterization of organic matter, supercritical CO2 extraction of oil in shale, experimental and simulation study of CO2-hydrocarbons counter-current diffusion in organic matter, recovery of oil in kerogen during CO2 huff 'n' puff process, and changes in microstructure of shale caused by CO2-kerogen interaction. The results presented in this paper show that at reservoir conditions, supercritical CO2 can spontaneously replace the hydrocarbons from the organic matter of shale formations. This mass transfer process is the key to releasing organic oil saturation and maximizing the capacity of carbon storage of a shale oil reservoir. It also presents a concern of the structure change of organic materials for long term CO2 sequestration with shale or mudstone as the sealing rocks.