The foam-drive process has been considered in the oil and gas industry as an enhanced oil recovery method. However, practical application of this process is rather restricted. The main limitation of foam field application is the complexity of its flow behavior in porous media. Nevertheless, the key advantage of foam over any gas drive process is that foam is less mobile than free gas, decreasing gas mobility and thus increasing oil recovery. In addition, it has been demonstrated that the foam flooding process assures substantial recovery of oil not otherwise recoverable by waterflooding or immiscible gas injection. This paper depicts a pore level visualization study, through visual observation of foam flooding in transparent etched-glass micromodels. In this study the effect of aqueous foam flooding and polymer enhanced foam flooding on residual oil recovery efficiency is evaluated. In addition, the effect of foam texture and porous media morphology on foam flood displacement performance is considered. Photographed and videotaped experimental results provide visual demonstration of high oil recovery efficiency, as a result of foam flooding. Image analysis shows that more than 90% of the residual oil in place can be recovered after waterflooding and gasflooding. Ultimately, visual observations demonstrate that foam flood displacement efficiency increases with porous media connectivity. The visualization experiments are also used to identify the pore level displacement mechanisms.
The residual oil of a reservoir depleted by conventional displacement processes is retained primarily because of heterogeneity in rock permeability, pore geometry, capillary or surface properties of the solid-fluid contacts, and the relative viscosity characteristics of the fluid phases. In some areas of the reservoir a large part of the oil has been displaced, leaving globules or small discrete masses of oil. In other areas of the reservoir, oil has been bypassed and remains isolated in the reservoir body. It thus may be reasoned that to displace the residual oil, any subsequent recovery process must provide the following:
means by which expulsive energy may be brought to unswept regions of the reservoir.
Surface or capillary forces that cause retention of the oil must be counteracted.
Viscosity effects, which permit extremely high rates of flow of the displacing medium relative to the oil flow rates, must be favorably modified.
The number of flow paths available exclusively to the movement of the displacing phase must be decreased.
Analysis of foam characteristics seems to indicate that injection of foam might fulfill these requirements and increase oil recovery.1 In fact, numerous experimental studies2,3,4,5,6,7,8,9,10,11 and field applications12,13,14 have demonstrated the foam capability as an oil recovery agent, and as a selective permeability reducing agent. Foam may be very useful in waterflooding and other oil recovery processes, where highly permeable streaks or unfavorable mobility ratios are a problem.2 In the case of waterflooding, foam decreases the permeability to water by developing a high trapped gas saturation. 2 The efficiency of miscible and immiscible gas drive methods can be improved by the foam process, since foam is less mobile than free gas. 3
