This paper deals with experimental evaluation of the effect of residual oil on the mobility reduction capabilities of foams at high temperature. Foam floods were carried out in 30 cm long, 5.6 cm diameter sand cores containing steamflood residual saturations of heavy crude oils, and involved measurements of steady-state pressure drop across the one core at various combinations of gas and liquid flow rates and surfactant concentration. The total amount of oil displaced by foam was determined by material balance and extraction of the core, by the Dean-Stark method. Five different foaming agents were evaluated using two types of heavy oils, and the effect of foaming agent concentration was studied.
The results show that the effect of residual oil on mobility reduction performance of a foam varies with the type of surfactant employed as well as with the nature of the oil. In some cases, the extent of mobility reduction in the presence of oil was more than two orders of magnitude greater than the oil-free case, while in others the presence of oil was detrimental to the performance of the foaming agent. Foam injection resulted in partial mobilization of steamflood residual oil regardless of whether or not effective mobility reduction was achieved. The role of emulsion formation was also investigated, and it was determined that it was not a major factor in these tests.
There is considerable interest in the use of foam forming surfactants for mobility control in steam floods. The effectiveness of the steam foam process is affected by a number of different factors. These include the thermal stability of the foaming agent, its adsorption on solid surfaces, and the flow properties of the foam within the porous medium. A number of previous publications have reported evaluations of these factors for various surfactants. 1–13 Field tests of steam foams have produced mixed results.1–16 One aspect of the steam foam process that has not received sufficient attention concerns the influence of residual oil on the mobility control characteristics of the foam.
In field applications of the steam foam process, the injected foam inevitably contacts some residual oil This contact between oil and foam can have a large effect on foam properties. Since most heavy oils contain naturally occurring surface active compounds, the mixing of the injected foaming agent with surfactants already present in the oil can lead to enhancement of foam properties when the two surfactants behave synergistically. On the other hand. when incompatible species are involved, the foam properties can deteriorate. Even without natural surfactants, oil can de-stabilize a foam by spreading at the gas/water interface. Partitioning of the foaming agent into the trapped oil and the formation of an oil-in-water emulsion can also be a factor in overall mobility reduction behavior.
The tests reported in this paper were carried out to quantify the effects of residual oil on the mobility reduction behavior of foams.