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CO2 injection has been recently proposed as an efficient method for oil recovery from shale reservoirs. However, significant amount of shale oil is still remaining in oil reservoirs after CO2 performance due to the reservoir heterogeneity and extremely low permeability. In this work, dimethyl ether is adopted as an additive in CO2 for enhancing shale oil recovery. The effect of dimethyl ether on the interfacial tension and viscosity of shale oil-CO2 systems are first measured. Using the low-field nuclear magnetic resonance (LFNMR) technique, dimethyl ether assisted CO2 injection is implemented on oil-saturated core samples to evaluate the performance of dimethyl ether as an additive in CO2 for shale oil extraction. Test results show that dimethyl ether decreases the interfacial tension of CO2-shale oil system more significantly compared to the traditional solvents, i.e., propane and n-butane. In addition, oil viscosity is more decreased when dimethyl ether is added. Based on the LFNMR tests, CO2 injection with the assistance of dimethyl ether is more efficient in recovering shale oil from the smaller pores, which is much higher than the traditional flooding scenarios, i.e., propane and n-butane assisted CO2 injection; dimethyl ether benefits to the solubility of CO2 in shale oil, which decreases the interfacial tension between CO2 and the in-situ oil and reduces oil viscosity at the same time. It enables a much higher shale oil recovery from the smaller pores. This study is expected to inspire new strategies that can be applied for shale oil reservoir development by adding cosolvents as an additive to CO2 for assisting CO2 injection.

CH4 and C2H6 are occupying components in shale gas. Determination of adsorption/desorption isotherms of CH4 and C2H6 on shale samples is significant for estimating the storage of shale resources in shale reservoirs. In this study, the thermogravimetric method is used to obtain the excess adsorption/desorption of CH4 and C2H6 on two typical shale samples. Simplified local density theory/Peng-Robinson equation of state (SLD-PR EOS) model is then applied to calculate the adsorbed density of CH4 and C2H6 on both shale samples, which is then applied to convert the measured excess adsorption into absolute adsorption values. Results show that C2H6 presents higher adsorption capacity than CH4 on shale samples, indicating the more affinity of C2H6 to the organic shale. Based on the predicted results from the SLD-PR EOS model, a reasonable agreement has been achieved with the measured adsorption isotherms, indicating the accuracy of the SLD-PR EOS model for predicting adsorption of CH4 and C2H6 on shale samples. In addition, the calculated adsorbed density of CH4 and C2H6 is a function of temperature and pressure, which agrees well with the results from the molecular simulations. The obtained absolute adsorption is always higher than the measured excess adsorption, emphasizing the importance of determination of adsorbed density in predicting the absolute adsorption of CH4 and C2H6 on shale. This study compares the adsorption/desorption behaviors of CH4 and C2H6 on typical shale samples, and more importantly, we propose a more efficient method, i.e., the SLD-PR EOS model, to calculate the absolute adsorption of CH4 and C2H6 on shale samples.