Impact of citrate ester surfactants on the MMP, extraction and swelling behaviors between CO2 and oil: Applications for enhanced shale oil recovery

The impacts of citrate ester surfactants on the MMP, extraction and swelling behaviors between CO2 and oil were investigated to enhance shale oil recovery. Firstly, the dissolution behaviors of citrate ester in CO2 and the influence of citrate ester on the MMP between CO2 and oil were investigated by the phase-transition-point measurement. Then, the effects of citrate ester on the extraction and swelling behaviors between CO2 and oil were explored by a newly-designed method. At last, the effect of surfactant on the shale oil recovery during CO2 huffn-puff process was discussed. The results show that compared with citrate ester B, citrate ester A has a lower cloud-point pressure and higher effect to decrease the MMP of oil and CO2. The extraction ratio and swelling ratio both increase with the increase of CO2 pressure and the increase of oil content in the oil and CO2 systems. Citrate ester A can enhance the extraction and swelling effects of CO2 to oil and the promoting effect increases with the increasing surfactant concentration. The presence of 1% citrate ester A in CO2 can enhance the oil recovery about 10% caused by the decreasing MMP, improvements of extraction, swelling and solution-gas-drive effects.