Effect of surfactant on oil displacement efficiency of imbibition/huff and puff in low permeability reservoirs

Low permeability and tight reservoirs are rich in microscale and even nanoscale pores, resulting in a large interfacial tension between oil and water in the pores. Surfactant can effectively improve the oil displacement efficiency during imbibition and huff and puff. In this paper, the low permeability cores with different permeability are taken as the research object, and the effects of surfactant and distilled water on the oil displacement efficiency of imbibition/huff and puff are compared and analyzed using the nuclear magnetic resonance technology. Results show that: (a) Huff and puff can significantly improve displacement efficiency, and there are mainly three reasons: the soaking time, surfactants improve infiltration efficiency, and elastic energy. (b) Imbibition is a spontaneous phenomenon in tight reservoirs, while huff and puff is artificially manipulated. (c) Due to the slow infiltration process, as the soaking time increases, the oil displacement efficiency increases. (d) when the pressure is increased from 0.1 MPa to 12 MPa, the oil recovery and displacement efficiency are increased by about 2 times. (e) Compared with imbibition displacement, huff and puff can significantly improve displacement efficiency. (f) The T-2 spectrum shows that the oil displacement efficiency of surfactant imbibition is higher, and the oil displacement efficiency of imbibition is significantly lower than that of huff and puff.