Chemical flooding of oil reservoirs .5. The multiphase behavior of oil/brine/surfactant systems in relation to changes in pressure, temperature, and oil composition

Multiphase PVT-studies are conducted on surfactant-brine-oil systems relevant for oil recovery processes. An alkyl-o-xylene sulfonate is used as surfactant, NaCl-solution as brine, and various types of live oil, i.e. crude oil, fraction of crude oil, and model oil. Solubilization parameters for the microemulsion phase are determined in the temperature range of 40-180 degrees C and the pressure range of 200-1000 bar. By increasing the pressure the trend in the phase behavior in all cases is II(+)/III/II(-). In the temperature scan the crude oil system showed a II(-)/III/II(+) phase behavior by increasing the temperature, while the model oil and the distillation cut of the crude oil without the heavy end fraction showed the opposite phase behavior, II(+)/III/II(-). The difference in the phase properties is discussed in terms of the resin-type compounds acting as cosurfactants, and the dissolution of water into the oil phase at high temperatures.