CO

2

injection may be the most effective method to enhance shale oil recovery due to its good injectivity and miscibility with crude oil.However

unlike conventional reservoirs

shale reservoirs usually feature fractures and micro/nano-scale pores

and thus whether CO

2

can enter micro/nano-scale pores to mobilize oil inside is the key to a successful CO

2

-EOR in shale reservoirs.Therefore

a CO

2

-EOR experiment was carried out to find out the features and mechanism of oil mobilization in the micro/nano-scale pores of shales by means of nuclear magnetic resonance (NMR).In addition

effects of total exposure time and times of exposure on recovery performance were also investigated.Both NMR T

2

spectrum and images indicate that oil in all shale pores can be effectively mobilized by CO

2

injection.The recovery factor is 32.63% for the first shale oil -CO

2

contact.The production rate is correlated to the exposure time:an initial fast-increa-sing stage followed by a declining stage hereafter.The CO

2

diffusion is the main mechanism driving the CO

2

-EOR in shale reservoirs.In conclusion

the study has proven that CO

2

injection serves to effectively enhance shale oil recovery

which may provide an analogy to the effective development of continental shale oil elsewhere.