Potential of dimethyl ether as an additive in CO2 for shale oil recovery

Abstract

CO2injection 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 CO2performance due to the reservoir heterogeneity and extremely low permeability. In this work, dimethyl ether is adopted as an additive in CO2for enhancing shale oil recovery. The effectof dimethyl ether on the interfacial tension and viscosity of shale oil-CO2systems are first measured. Using the low-field nuclear magnetic resonance (LFNMR) technique, dimethyl ether assisted CO2injectionis implemented on oil-saturated core samples to evaluate the performance of dimethyl ether as an additive in CO2for 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 andn-butane. In addition, oil viscosity is more decreased when dimethyl ether is added. Based on the LFNMR tests, CO2injection 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 andn-butane assisted CO2injection; dimethyl ether benefits to the solubility of CO2in shale oil, which decreases the interfacial tension between CO2and 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 CO2injection.