Compositional dependence of wetting and contact angles in solid-liquid-liquid systems under realistic environments

Document Type

Conference Proceeding

Publication Date

12-1-2005

Abstract

The wetting and contact angles in porous media are important for the characterization of multi-phase flow behavior. However, when the two immiscible fluids coexist, the adhesion and spreading of wetting phase are largely influenced by each of the components present in both the fluids. When compared to polar components such as asphaltenes in the oil-phase, which have been widely believed to be a major source of oil-wetting characteristics, the effect of light gaseous ends (methane to pentane) present in the oil on wetting is rarely studied. This is mainly due to the difficulty in measuring contact angles with live oil at elevated pressures and temperatures. Hence, in this study, the Dual Drop Dual Crystal (DDDC) contact angle measurement technique has been used with a high-pressure high-temperature optical cell apparatus to measure dynamic contact angles of live crude oil and brine on different rock substrates. The effect of light gaseous ends in crude oil on wetting is studied by depleting the pressure at regular intervals during the experiments. The light ends partially came out of oil phase when the pressure declined below the bubble-point pressure of crude oil (4.7 MPa). The variation of contact angles observed with the pressure during the pressure depletion clearly showed the influence of light ends on wetting. The water-advancing contact angle of live crude oil gradually increased from 55° at bubble point pressure to 154° at ambient pressure. The de-asphaltened and the deresined crude oils showed the similar strong oil-wet characteristics as stocktank crude oil. Contrarily, the addition of asphaltenes to toluene induced strong oil-wet behavior. These observations indicate that the asphlatenes could shift the wetting characteristics towards oil-wet but they may not be solely responsible for oil-wetting behavior observed in oil-brine-solid systems. The light gaseous ends in oil phase appear to peptize the asphaltene molecules by surrounding them, thereby preventing their agglomeration and migration to the interface. The differences observed in the behavior of dynamic interfacial tensions between live and stocktank crude oils further substantiates the influence of light gaseous ends on the activity of polar components in live oil. In addition to oil compositional effects, the influence of solid surface roughness, mineralogy of rock substrates as well as the brine composition on wetting and contact angles have also been investigated. For highly smooth substrates, carbonate and silica showed relatively similar high water-advancing contact angles, while for rough substrates, the advancing contact angles on silica were much lower compared to the carbonates. The multivalent ions in the brine increased the water-advancing contact angle, while the monovalent ions decreased the advancing contact angles. The ratio of multi to monovalent ions influenced the oil spreading on the rock substrates. Thus, this paper discusses in detail the comprehensive effects of all the fluid components that control the wetting behavior in solid-liquid-liquid systems and provides several mechanistic explanations for various compositional effects observed during the course of this experimental study. © 2005 IEEE.

Publication Source (Journal or Book title)

Proceedings - 2005 International Conference on MEMS, NANO and Smart Systems, ICMENS 2005

First Page

50

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