We use confocal microscopy to measure velocity and interfacial tension between a trapped wetting phase with a surfactant and a flowing, invading nonwetting phase in a porous medium. We relate interfacial tension variations at the fluid-fluid interface to surfactant concentration and show that these variations localize the destabilization of capillary forces and lead to rapid local invasion of the nonwetting fluid, resulting in a Haines jump. These spatial variations in surfactant concentration are caused by velocity variations at the fluid-fluid interfaces and lead to localization of the Haines jumps even in otherwise very uniform pore structure and pressure conditions. Our results provide new insight into the nature of Haines jumps, one of the most ubiquitous and important instabilities in flow in porous media.

中文翻译：

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Haines跳跃过程中多孔介质中的表面活性剂变化使毛细血管局部失稳。

我们使用共聚焦显微镜来测量表面活性剂截留的润湿相与多孔介质中流动的侵入性非润湿相之间的速度和界面张力。我们将流体-流体界面处的界面张力变化与表面活性剂浓度相关联，并表明这些变化使毛细作用力的不稳定化局部化，并导致非润湿性流体快速局部侵入，从而导致海恩斯跃迁。表面活性剂浓度的这些空间变化是由流体-流体界面处的速度变化引起的，即使在非常均匀的孔隙结构和压力条件下，也导致Haines跳变的局部化。我们的结果为海恩斯跳跃的性质提供了新的见解，海恩斯跳跃是多孔介质中流动中最普遍和最重要的不稳定性之一。