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The successful development of shale oil is significant to provide oil steadily. The comparisons of enhanced shale oil recovery by CO 2  flooding and huff-n-puff methods for shale cores without and with fractures were investigated by nuclear magnetic resonance (NMR) spectra and physical simulation experiments. The effects of injection pressure and injection amount on enhanced shale oil recovery by CO 2  flooding were considered, as well as the displacement mechanism of oil at different sections of the core. With the increases of injection pressure and injected PV, the oil recovery of CO 2  flooding increases while the utilization efficiency decreases. The oil recoveries of CO 2  with 2PV are 14% and 23% at 9 and 18 MPa, meanwhile, the values of the produced oil amount per mole of CO 2  are 7% and 5% at 9 and 18 MPa. The oil content near the inlet of the core decreases greatly with the increasing PV while the oil content near the outlet has a slight decrease. After CO 2  injection of 7 PV, the oil content near the outlet is still as high as 80%. Moreover, the factors of pressure, cycles, and soaking time were examined for CO 2  huff-n-puff. The oil recovery increases while the utilization efficiency decreases with the increasing pressure and cycles in CO 2  huff-n-puff. The total oil recoveries after three cycles are 56% and 69% at 9 and 20 MPa, while the values of the produced oil amount per mole of CO 2  are 42% and 20%. With the increase of cycle, the swept area increases and the displacement efficiency of the swept core has a great enhancement. Compared with CO 2  flooding, CO 2  huff-n-puff method has greater oil recovery and CO 2  utilization efficiency because of the sufficient contacting time between oil and CO 2  and high swept ability. Therefore, CO 2  huff-n-puff is beneficial for shale oil production. This work can provide the optimized method and parameters for the production in Enan Chang 7 zone.

Nuclear magnetic resonance study on enhanced shale oil recovery by CO 2 injection: A case study