Abstract: The microscopic imbibition mechanism of surfactants is a key factor affecting imbibition recovery in tight oil reservoirs. At the nanoscale pore level, the coupling between solid-liquid interfacial characteristics and fluid transport behavior becomes increasingly complex, resulting in unclear imbibition behavior in tight reservoirs; therefore, it is essential to clarify the microscopic imbibition mechanisms and phase behavior evolution of surfactant systems. Taking tight reservoirs in Ordos Basin as the research subject, three imbibition systems with distinct solid-liquid interfacial characteristics, including brine, conventional surfactant (AES), and in-situ microemulsion (SDBS-APS), were constructed. Low-field nuclear magnetic resonance (NMR) and nanofluidic techniques were employed to systematically conduct core-scale imbibition experiments and nanoscale pore-scale visualization experiments. A mathematical model for microemulsion imbibition was subsequently established. The results indicate that:(1) The core imbibition recovery factors of brine, AES, and SDBS-APS are 14.5 %, 26.1 %, and 34.3 %, respectively. (2) SDBS-APS exhibits ultra-low interfacial tension and solubilization-emulsification capabilities, enabling more uniform vertical sweep in the core to effectively mobilize oil in deep reservoirs. (3) SDBS-APS can diffuse into the oil phase within nanopores, inducing the solubilization of interfacial films to form extensive microemulsion zones. (4) By incorporating solubilization coefficients and time parameters into the oil-water imbibition mathematical model, the relationship between oil saturation and imbibition distance under ultra-low interfacial tension conditions was established, achieving dynamic prediction of recovery efficiency.

Key words: tight oil reservoir, imbibition, surfactant, nuclear magnetic resonance, nanofluidic, mathematical model

摘要： 表面活性剂的微观渗吸机制是影响致密油储层渗吸采收率的关键因素,尤其是在纳米尺度孔隙中,固液界面特征与流体传输行为的耦合关系更加复杂,导致流体在致密储层中的渗吸行为不清晰,因此必须明确表面活性剂的微观渗吸机制及相态演化规律。以鄂尔多斯盆地致密储层为研究对象,构建了盐水、常规表面活性剂(AES)、原位微乳液(SDBS-APS)3种具有不同固液界面特征的渗吸体系,采用低场核磁共振和纳流控技术,深入开展了岩心尺度渗吸实验和纳米孔隙尺度微观可视化渗吸实验研究,建立了适用于微乳液体系的渗吸数学模型。研究结果表明:①盐水、AES和SDBS-APS的渗吸采收率分别为14.5 % 、26.1 % 和34.3 %;②SDBS-APS微乳液具有增溶乳化能力,能将油水界面张力降低至超低水平,实现岩心更均匀的纵向波及,有效动用岩心深部油相;③SDBS-APS微乳液能在纳米级孔隙中扩散进入油相内部,诱导界面膜增溶形成大面积微乳液带;④将增溶系数和时间参量引入油水渗吸理论数学模型,建立了超低界面张力环境含油饱和度与渗吸距离的关系,实现了采收率的动态预测。

关键词: 致密油藏, 渗吸, 表面活性剂, 核磁共振, 纳流控, 数学模型