Studies of Water-in-Oil Emulsions: Stablity and Oil Properties

摘要

This paper summarizes studies to determine the stability of water-in-oil emulsions resulting from asphaltene or resin content and viscosity stabilization into three categories: stable, unstable and meso-stable. Water can also reside in oil as 'entrained water', in whick larger droplets of water are temporarily suspended by viscous forces. These have been distinguished by physical measures as well as visual differences. The viscosity of a stable emulsion at a shear rate of one reciprocal second, is at about three orders-of-magnitude greater than that of the starting oil. An unstable emulsion usually has a viscosity no more than about 20 times greater than that of the starting oil. A stble emulsion has a significant elasticity, whereas an unstble emulsion does not. A meso-stable emulsion has properties between stable and unstable, nowever breaks down after a few days of standing. The usual situation is that emulsions are obviously either stable, meso-stable or unstable. Entrained water, water suspended in oil by visous forces alone, is also evident. Very few emulsions have questionable stability. Analystical techniques were developed to test these observations. Studies in the past four years have shown that a class of 'verystable' emulsions exists, characterized by their persistence over several days to years. These stable emulsions actually undergo an increase in viscosity over time. Monitoring of all water-in-oil states resulting from oil/water mixtures prepared in this study, has been performed for at least one week. This show that meso-stable emulsions, unstable emulsions and entrained water states clearly separate into oil and water layers. Stable emulsions increase in apparent viscostiy and elasticity. The stability of emulsions has been studies by examining the asphaltene and resin content and secondarily, the visco-elast properties of eight-two oils. results are reported which show that these factors are resposible for the stability regimes moted.