There has been much interest in recent years in the application of mobility control foams to improve the sweep efficiency of steam and gas miscible EOR processing. While it seems to be well established that foams can reduce gas mobility in oil-free systems, the effect of an oil phase on a foam is less understood.
This paper summarizes work that was carried out with the aim of gaining a better understanding of foam-oil interactions. A number of foam-forming surfactants were tested for their sensitivity to different crude oils using the following approaches: foaming capacity in a blender at atmospheric pressure, foaming capacity in a high pressure visual cell, visual observation in a glass micromodel, mobility reduction in core floods, and measurement of phase behavior and interfacial properties. Mixtures of surfactants that generate oil-sensitive and oil insensitive foams were also tested.
The results indicate that for the systems studied here the sensitivity of a foam to oil strongly depends on surfactant type, but is not affected as strongly by the type of oil. It is also shown that blending of surfactants may allow the formulation of systems with a desired degree of oil sensitivity.
The application of foams as mobility control agents for gas flooding applications LS a developing technology. The Petroleum Recovery Institute (PRI) has been involved 1n research aimed at developing this EOR technology for application in the Beaverhill Lake Carbonate and Gilwood Sand reservoirs and has identified several classes of surfactants suitable for use with the extremely high salinity brines found in these reservoirs. However, it has been observed that the presence of an oil phase can be detrimental to foams generated by most of these surfactants.
This paper describes work performed in an attempt to better understand the interactions between surfactant foams and crude oils so that foam sensitivity to crude oil can be predicted and possibly even controlled for improvement of oil recovery processes that employ foams.
Laboratory experiments designed to evaluate foaming surfactants for use as mobility control or blocking and diverting agents in oil reservoirs have in the past examined several aspects of surfactant performance. These include a surfactant's solubility, thermal (chemical) stability, foaming capacity, bulk foam stability, ability to generate a reduction in the mobility of fluids injected into a porous medium and adsorption/desorption phenomena. These subjects have been discussed in previous PRI publications, 1–5 as well as in numerous papers from other laboratories. One area of investigation which has been less thoroughly examined is the interaction of foam with a residual oil phase. This last topic is the focus of this paper, which describes preliminary efforts to understand the nature of the interaction between foams and crude oils.
It has been observed that the presence of a residual oil phase can significantly affect the pressure drop generated across a core. Previous research carried out at PRI4 has shown that light oils have a detrimental effect on the mobility reduction factor (MRF), presumably by disturbing the foam generation and propagation processes.