Abstract Surfactants improve oil recovery from tight oil-wet formations through wettability alteration and interfacial tension (IFT) reduction. The popular perspective believes that wettability alteration induced capillary-driven spontaneous imbibition is the major mechanism of Enhanced Oil Recovery (EOR) in tight oil reservoirs. Therefore, surfactant with functions of wettability alteration while guarding a relatively high IFT should be chosen as the best candidate. However, ultra-low IFT may change the phase behavior and flow-pattern within the porous media to improve the oil recovery through emulsification. Therefore, in this paper, we investigated the effect of spontaneous emulsifying surfactants on the oil recovery from tight sandstones through spontaneous imbibition experiments and the results are compared with that of regular surfactants The results manifested that the spontaneous-emulsifying surfactants with ultra-low IFT can improve oil recovery from oil-wet cores, and the performance surpassed that of regular surfactants through wettability alteration. It is because a spontaneous-emulsifying surfactant is capable of accelerating the oil dispersion and reducing the residual oil saturation by emulsifying the oil phase. Partly, it diffuses out from the porous media in the form of the microemulsion, and partly small oil droplets with ultra-low IFT may coalesce into larger ones so that it is easy for them to deform and to be produced by buoyancy. Therefore, comparing with the traditional viscous flow, the change of the flow pattern due to the addition of spontaneous-emulsifying surfactants further enhanced the recovery in term of producing rate and final recovery factor.

中文翻译：

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自发乳化对致密油湿油藏采收率的影响

摘要 表面活性剂通过润湿性改变和界面张力 (IFT) 降低来提高致密油湿地层的石油采收率。普遍认为，润湿性改变引起的毛细管驱动自吸是致密油藏提高采收率（EOR）的主要机制。因此，应选择具有润湿性改变功能同时保护较高 IFT 的表面活性剂作为最佳候选者。然而，超低的 IFT 可能会改变多孔介质内的相行为和流动模式，从而通过乳化提高石油采收率。因此，在本文中，我们通过自吸实验研究了自发乳化表面活性剂对致密砂岩采油率的影响，并将结果与​​常规表面活性剂的结果进行了比较。结果表明，具有超低 IFT 的自发乳化表面活性剂可以提高石油采收率。湿核，通过润湿性的改变，性能超过了普通表面活性剂。这是因为自乳化表面活性剂能够通过乳化油相来加速油的分散并降低残余油饱和度。一部分以微乳液的形式从多孔介质中扩散出来，一部分具有超低IFT的小油滴可能会聚结成较大的油滴，从而容易变形并产生浮力。所以，