(132c) Revisiting the Dynamic Evolutions of Crude Oil-Air and Crude Oil-Water Interfacial Properties

In this paper, crude oil-air and crude oil-water interfacial properties are investigated qualitatively and quantitatively over wide ranges of temperatures and pressures. Dynamic interfacial tensions of the crude oil-water and crude oil-air interfaces were measured and relevant influence factors were analysed.

Three crude oils were investigated. Dynamic surface tensions of the crude oils were measured at atmospheric pressure and temperatures of 20-120°C, while dynamic interfacial tensions of the crude oils against deionised water were measured at temperature and pressure up to 120°C and 300 bar, respectively. Additionally, a microscope fitted with a heated stage was used to observe precipitation of (possibly surface-active) components in the oils within the target temperature range. A series of mathematical models was employed to aid the interpretation of the surface/interfacial phenomena and conformational changes through the quantifications of molecular diffusion and adsorption/desorption.

The dynamic behaviour of the surface tension (ST) and interfacial tension (IFT) was found to be qualitatively different. Upon forming a pendant oil droplet in air, the surface tension was found to increase monotonically with time, approaching an asymptotic limit. Conversely, with a sessile oil droplet formed in deionised water, the interfacial tension was observed to decrease rapidly over an initial period on the order of 10 min. Following this, the IFT was observed to either (a) plateaux or (b) pass through a minimum and increase again, over a further period ~ 100 min, towards an asymptotic limit in between the initial and minimum values. The initial rapid decrease in IFT is attributed to surface active components diffusing towards the interface, where they are more- or less-strongly adsorbed. A subsequent increase in the IFT was observed with one particular oil and this might be attributed to surface reconfiguration through dissolution of surface active components into the surrounding water and/or formation of asphaltene flocs at the interface.

Interfaces of crude oil-water/air are of great importance in oil/gas exploration and post-production carbon geological storage. Most previous scientific studies simply used synthetic hydrocarbons while actual crude oil samples were barely studied. This study addresses key knowledge gaps in respect of crude oil-water/air interfacial phenomena by combining experimental measurements with theoretical interpretation. The results will be applicable for all academic and industry subjects where the crude oil-water/air interfaces occur.