Toward an improved understanding of emulsion stabilization at elevated temperatures by direct visualization and reversibility analysis

Abstract

Harsh conditions of high temperature are often encountered during production and application of emulsions. For example, in crude oil recovery, the emulsification performance of natural emulsifiers in oil at elevated temperatures is crucial but rarely studied, largely due to the lack of appropriate apparatus. In the present work, the emulsion stabilization by asphaltenes and fines at elevated temperatures up to 200 °C was investigated by using a custom-made windowed cell, which permits real-time direct visualization of the emulsion phase. The temperature-reversibility of the prepared emulsions was analyzed under our controlled heating and cooling temperature cycle program. The resultant emulsions at room temperature from the proposed apparatus are consistent with the results obtained from the most widely used bottle test approach, confirming its validity. The emulsion volumes significantly reduced with the increasing temperature in both cases of asphaltenes and fines by 100% and 62% at maximum, respectively. The asphaltenes were unable to stabilize emulsions at the temperature of 150 °C and higher, while the fines can stabilize a 12 vol% emulsion layer even at 200 °C. Under our temperature cycle program, the asphaltenes-stabilized emulsions were reversible, indicating that the adsorption and desorption processes of asphaltenes from the interfaces did not irreversibly alter their interfacial activity. In contrast, the volumes of emulsions stabilized by the fines generally remained unchanged during the cooling operations, suggesting that the temperature-induced desorption of the Pickering particles from the interfaces irreversibly affects their re-adsorption. The high thermal stability of fines-stabilized emulsions is beneficial for their application in enhanced oil recovery at harsh reservoirs. The novel method of temperature-reversibility analysis is an effective tool to explore the stabilization mechanism of emulsion systems.