Asphaltene instability in the presence of emulsified aqueous phase

Abstract

Water cut of high salinity, which is reported to be on the rise in many reservoirs, may profoundly exacerbate asphaltene related problems. In this work, the impact of the emulsified aqueous phase in synthetic oils on asphaltene precipitation has experimentally been studied. The oil phase of each emulsion was divided into three sub-fractions of oils 1, 2, and 3, based on their asphaltene’s affinity to interact with the oil/water interface. These three sub-fractions were then contacted with n-heptane as precipitator. The influence of ion types, temperature, and finally the presence of tetrahydrofuran (THF) in emulsified aqueous phases were further investigated for two different asphaltene samples. Moreover, the role of ions on asphaltene interaction with the oil/water was examined using interfacial tension, interfacial rheology, and droplet size analysis. The results showed that precipitation behavior of oils 1, 2, and 3 would be controlled by changes in relative distribution of asphaltene sub-fractions and their respective concentration. IFT measurements showed that asphaltenes in oils 1, 2, and 3 have different interactions with de-ionized water. Ions of higher valence, like Fe3+, also would profoundly decrease the size of water droplets in emulsion and also cause more asphaltene to remain in emulsions. When THF was added to the injected aqueous phase, then it got partitioned between aqueous and oleic phases. Thus, its addition to the emulsified aqueous phase firstly stemmed emulsion formation, and secondly, it alleviated asphaltene precipitation by diluting the oil phase at the oil/water interface. IFT measurements showed that asphaltenes in oils 1, 2, and 3 had different interactions with the de-ionized water. It was shown that brines did not directly affect the asphaltene precipitation. Instead, their presence had a noticeable impact on the distribution of asphaltene between the bulk of the oil and emulsion phases. This, in turn, altered the precipitation of asphaltene of the oil. The findings of this study address the main concerns about asphaltene destabilization by aqueous phase injection to petroleum reservoirs.