| Tight sandstone reservoir is an important unconventional oil and gas resource in China,and spontaneous imbibition is its important oil displacement mechanism.Surfactant solution is widely used as assisted imbibition in tight sandstone reservoirs,but the microscopic mechanism of its action is still unclear.Taking the tight sandstone reservoir core of Yanchang Formation 7 in Ordos Basin as the research object,the mineral composition of the reservoir was analyzed by FIB-SEM and QEMSCAN scanning technology,and the molecular simulation physical model of tight sandstone was established.Molecular dynamics method is used to simulate the interaction between surfactant solution and oil phase on the rock surface.In addition,sodium fatty alcohol polyoxyethylene ether sulfonate(AESO-3),sodium-alkenyl sulfonate(AOS),sodium dodecylbenzene sulfonate(SDBS),and sodium dodecyl sulfate(SDS)were selected for core imbibition experiments,and the effects of surfactant type and concentration on reducing interfacial tension,wettability change,imbibition rate,and oil recovery were explored.The results show that the mineral composition of Chang 7 reservoir in Yanchang Formation of Ordos Basin mainly includes Shi Ying and feldspar,with intergranular pores developed and filled with clay minerals.Molecular dynamics simulation shows that AESO-3 can reduce the formation energy of the oil-water interface,increase the thickness of the oil-water interface,make it more stable,and reduce the contact angle of rockwater-oil.Core imbibition experiments show that the imbibition displacement effect of AESO-3 is the best at the same concentration.Before reaching the critical micelle concentration,the imbibition rate and recovery rate decrease with the increase of surfactant concentration,and the wettability of AOS and AESO-3 is stronger.The research results are helpful to reveal the mechanism of surfactant flooding and improve the recovery factor of tight reservoirs. |
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