Effect of Injection Pressure on CO2 Huff-n-Puff in Low-Permeability Sandstone Cores Using Nuclear Magnetic Resonance

In order to figure out the micro-scale recovery degree of different pore sizes, the T2 spectrum of low-permeability sandstone cores before and after CO2 huff-n-puff is obtained using NMR technique. The results show that the micro-scale recovery degree increases with increase of pore sizes. Oil in macropores and medium pores is more easily produced, and Oil in micropores is difficult to recover at 7-12MPa. The total recovery degree of three cores increases with the increase of injection pressure. This study is expected to be significant for understanding the mechanisms of CO2 huff-n-puff for enhancing oil recovery in low-permeability sandstone reservoirs.