Method and apparatus for characterizing interfacial tension between two immiscible or partially miscible fluids

An apparatus for characterizing interfacial tension between a non-wetting phase fluid and a wetting phase fluid of a slug flow, comprising:

• a capillary structure configured to contain a slug of the non-wetting phase fluid of the slug flow, the slug having a leading edge meniscus and a trailing edge meniscus, and the capillary structure having a venturi-like section;
• a pressure sensor configured to measure differential pressure between first and second locations of the capillary structure, the first location disposed upstream of the leading edge meniscus of the slug with the leading edge meniscus of the slug contained within the venturi-like section of the capillary structure, and the second location disposed downstream of the trailing edge meniscus of the slug;
• and
• data processing means, operably coupled to the pressure sensor, for deriving a measure of interfacial tension between the non-wetting phase fluid and the wetting phase fluid of the slug flow based upon the differential pressure measured by the pressure sensor.