A Review of Carbon Dioxide Adsorption to Unconventional Shale Rocks Methodology, Measurement, and Calculation

Carbon dioxide (CO2) injection has been applied extensively in hydrocarbon reservoirs for both increasing oil recovery and CO2 storage purposes. Recently, CO2 injection has been proposed to increase oil recovery and for CO2 storage in shale reservoirs. During CO2 injection in shale reservoirs, adsorption will take place on the surface of the rock, which will impact both the oil recovery and the storage capacity. This research provides a roadmap to the different types of adsorption and the adsorption measurements and calculations with emphasis on the ones most applicable during CO2 injection in shale reservoirs. The main two types of adsorption are initially explained including physisorption and chemisorption, and the major applicable adsorption isotherms are explained and their limitations are listed. The research then focusses on physisorption and its types, and hysteresis trends since chemisorption does not occur in shale reservoirs during CO2 injection. The different methods used to measure adsorption are then illustrated and explained including volumetric, gravimetric, volumetric-gravimetric, oscillometry, and impedance spectroscopy. The different calculation methods for volumetric adsorption are then explained. Finally, the most common errors that have been observed during measurement and calculation of adsorption are listed and explained, while mentioning the method to avoid each error. This research provides a guideline to the proper and accurate measurement of CO2 adsorption on shale rock during enhanced oil recovery applications and CO2 storage operations in unconventional shale reservoirs to improve the productivity and applicability of this application