Evaluation of supercritical CO2 fracturing effect in Da 'an reservoir of Songliao Basin

Carbon dioxide (CO2) fracturing technology is introduced to improve the development effect of low permeability reser-voirs. To understand the advantages of CO2 fracturing and the mechanism of CO2 assisting oil displacement efficiency, laboratory core displacement experiments and nuclear magnetic resonance (NMR) tests are conducted. For core dis-placement experiments, a water flooding, a water flooding-CO2 huff and puff experiment are conducted. Water flooding simulates the oil displacement after hydraulic fracturing and the latter simulates the effect after CO2 fracturing. Fur-thermore, an NMR test is conducted in each stage of the experiments to quantify the recovery degree of crude oil in different pore throats for a low-permeability reservoir. The results show that the water flooding recovery of the two cores is 31.26% and 30.14%, respectively. The CO2 huff and puff enhanced oil recovery and subsequent water flooding are 11.48% and 5.19%, respectively. Compared with conventional hydraulic fracturing, CO2 fracturing enhanced oil recovery by 15.55%. Furthermore, the crude oil recovery degree of water flooding in macro-pores is 75.71%, while that in mesopores is 62.17% and that in small pores is 7.49%. After CO2 huff and puff, the recovery degrees in macrop-ores, mesopores, and small pores are 99.10%, 67.51%, and 23.21%, respectively. It demonstrates CO2 can penetrate deeply into the tiny pores that cannot be affected by water flooding for oil displacement, effectively increasing the swept volume and improving the oil recovery. Research shows the advantages of CO2 fracturing and may help to enlarge its application in low-permeability reservoirs.