(563d) Study of the Influence of Antifoaming Additives on the Crude OIL/Air Interface By Rheology

Each crude oil reservoir has unique conditions of temperature and pressure, where the crude oil has different amounts of dissolved gas in its constitution. During production, as the fluid rises in the pipes, the pressure and temperature decrease, causing the previously dissolved gas to be liberated. This activity, along with the agitation that occurs during the extraction process, leads to the formation of foams.

The foams generated during oil production are complex systems, making it hard to understand what occurs in the foam layers, due to the complexity of their continuous phase. Some studies have shown that the main species that stabilize foams are asphaltenes, because they reduce the surface tension of the bubbles due to their interfacial activity. The interfacial layer of the foam becomes viscoelastic due to the presence of these amphiphilic species, which have superficial action and can be adsorbed through the dispersed or continuous phase. Therefore, rheological analysis of this interface is necessary to understand its characteristics and stability, since the lifetime of this foam is closely associated with these conditions.

Interfacial rheology also provides information on the functional interplay of the deformation of an interface, the forces acting on it and the resulting flows in the adjacent phases of the fluid. This can be accomplished by dilatation and shear methods.

The aim of this work was to study the crude oil/air interface of different crude oil samples and different antifoaming products using the BiCone accessory, which is used in the shear method.

The tests of the foam formation in crude oil and the rheology of the crude oil/air interface were performed with or without the presence of antifoaming additives, using two samples of crude oil from Brazilian wells (P1 - 19 °API and P2 - 26 ^oAPI).

In this study, commercial silicone-based antifoaming agents and formulations composed of a nonionic surfactant based on poly(ethylene oxide) were used.

The tests of the foam formation in the two crude oil samples were carried out according to the method described by Fraga¹ and Rezende². The tests were performed using a Fann High Temperature Aging Cell® and a Fann 704Es roller oven. All the tests were performed in duplicate and the means of the data were used to plot the graphs. The tests in the presence of the antifoaming additives were carried out at concentrations of 20 ppm or 100 ppm.

The rheological properties of the interfacial films of the crude oil/air systems were determined with a Haake MARS 60 rotational rheometer using the BiCone accessory. The main objective of this study was to observe the influence of the antifoaming formulations on the values G’ and G” (elastic modulus and viscous modulus, respectively) of the interfacial films, since these properties are very important to understand the antifoaming action mechanism at the crude oil/air interfacial layer.

In all the tests, the crude oil samples, with or without the antifoaming formulations, were left in the accessory for 17 hours (aging time), to assure adsorption of the asphaltenic fractions at the crude oil/air interface. We performed oscillatory shear tests with variation to time but constant shear rate of 10% and frequency of 1 Hz.

The results indicate there was a reduction of the G’/G” ratio of the interfacial film formed by sample P1 and P2 with addition of 20 ppm of the commercial antifoaming agents in relation to the pure crude oil. This interfacial rheology result corroborates the results of the tests of foam formation efficiency, where it was possible to observe that the height of the foam formed by that crude oil sample with the addition of additives was considerably lower than that of the pure crude oil.

The study reported here showed that rheology measurements of the crude oil/air interface utilizing the BiCone accessory can be correlated with foam formation tests of crude oil samples.

References:

1. Fraga, A. K.; Rezende, D. A.; Santos, R. F.; Mansur, C. R. E. Braz. Petrol. Gas. 2011, 5(1), 25-33.

2. Rezende, D. A. Bittencourt, R. R., Mansur, C. R. E. Petrol. Sci. Eng. 2011, 76, 172-177.