Foamy oil transport as a multiphase flow system

Résumé

In some heavy and extra heavy oil production fields in Venezuela the oil production occurs due to the gas in solution, which tends to form a foam, consisting of a dispersion of gas and water in oil. Foamy oil behavior at reservoir conditions and its transport process through porous media have been the focus of many multiphase flow researches. However, few studies have been developed at surface conditions, in which the oil viscosity increases considerably and the gas bubbles that are trapped in the foamy oil are expanded due to the change in pressure and temperature. Transportation of foamy oil through pipelines is a challenge in Venezuelan fields due to the relatively high gas volumes produced with oil. Part of this gas is dispersed as foam and the rest flows as a separate phase generating different flow patterns in the pipelines. This experimental study is focused on the behavior of a multiphase mixture composed by foamed emulsion, with high oil viscosity flowing through horizontal pipelines. The evaluated conditions correspond to 8.5 wt.% water, 1.5 wt.% surfactant and 90 wt.% mineral oil, pressures up to 255 kPa, temperature of 20°C, superficial gas velocities between 0.92 - 17.56 m/s and superficial liquid velocities between 0.04 - 1.07 m/s, with pipeline diameters of 0.0243 and 0.0508 m. Three different flow patterns were obtained: foamy stratified, foamy slug and foamy annular. Foaminess and foam stability were found to be dependent on the operational conditions. Foamability increases with the increment of the gas and liquid flow rates, while foam stability tends to decrease when the liquid flow rate increases and the gas flow rate decreases.