The Challenge

To increase the efficiency of the sweep by injecting gas as a foam instead of just gas. However, foams typically break down in the presence of oil.

Investigation

Using microvisual cells in the labs at the Petroleum Recovery Institute (PRI), we observed various interactions between foams and oil. The theories developed were compared with coreflood tests using foams flowing through rock samples at residual crude oil saturation.

Results

First, the identification of oil resistant foams; second, oil displacement can be increased by using moderately oil resistant foams.

Background

There is considerable interest in the application of foams in enhanced oil recovery processes involving miscible or immiscible gas displacement (CO2, hydrocarbon gases etc.). From a reservoir perspective foams can provide a means to counteract the displacing agent's naturally high mobility and low density and therefore can reduce fingering (channelling) and gravity override. Foams can also be applied near-well to reduce gas coning. Reference [1] provides a review of such applications.

In any reservoir application of foam there will come a point at which foams come into contact with residual oil and it has become common to hear the comment that it is impossible to make foams that will be stable in the presence of crude oil. After all, oils such as Castor oil are among the earliest chemicals to be used for foam inhibition and foam breaking. Even crude oils have been successfully used as defoaming agents in various industrial processes.

In order to test the validity of the prevailing paradigm we started to observe foam - crude oil interactions in microvisual cells for a variety of different foams [2]. This work immediately brought to light the fact that foams exhibit a wide range of sensitivities to the presence of crude oils. In fact three degrees of stability, ranging from completely oil resistant to extremely oil sensitive, have been distinguished. These characterizations depend on the extent to which the oil can become imbibed into the foam, as illustrated in Figure 1. That these stabilities translate into foam effectiveness in real porous media was shown in subsequent work with coreflood tests at waterflood residual oil saturation [3]. Related research has focussed on learning how the wettability of an oil-bearing porous medium influences foam performance [4].

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Figure 1. Degrees of oil sensitivity of foams from micromodel visualization.

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Some very important results have been derived from this work. First, we have clearly shown that it is indeed possible to make foams that are oil resistant, or retain their native stability in the presence of crude oil. This holds true for crude oils of different gravity, from light through heavy crude oils [5]. These oil resistant foams may be made with relatively pure foaming agents, which is usually quite expensive, or else with specially formulated mixtures, which can be cost-competitive with traditional foaming agents that do not have the desired insensitivity to crude oil. This technology is now ready for the field: a PRI patent [6] describes the field application of oil resistant foams made from formulations of a fluorocarbon surfactant mixed with either anionic or amphoteric hydrocarbon surfactant(s).

Secondly, we have found that we can make foams that have a moderate sensitivity to the presence of crude oil but still retain sufficient stability to be used in an oil recovery process, and which have the additional property of being able to emulsify and imbibe oil into the foam, where it can be transported. This amounts to a new kind of microscopic oil displacement and means that foams can be used to increase oil recovery not only by improving sweep efficiency, but also by microscopic displacement and transport (Figure 2). Two PRI patents describe the selection or formulation [7] of appropriate surfactant compositions and the field application [8] of foams that can function both to improve sweep eficiency and to imbibe and transport oil.

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Figure 2. Illustration of coreflood incremental recoveries due to oil imbibition and transport by foams.

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These are examples of technology developed for field application of foams which rely, in part, on the ability to generate and propagate foams having reasonable degrees of stability in the presence of crude oil. Both are currently available for field development and licensing. The myth that it is impossible to make foams having a practical stability in the presence of crude oil has now been debunked.

References

1. Schramm, L.L. (Ed.), Foams: Fundamentals and Applications in the Petroleum Industry, American Chemical Society: Washington, D.C. (1994).

2. Schramm, L.L. and Novosad, J.J., Micro-visualization of foam interactions with a crude oil: Colloids and Surfaces, 46, 21-43 (1990).

3. Schramm, L.L., Turta, A. and Novosad, J.J., Micro-visual and coreflood studies of foam interactions with a light crude oil: SPE Res. Eng. 8(3) 201-206 (1993).

4. Schramm, L.L. and Mannhardt, K., The effect of wettability on foam sensitivity to crude oil in porous media: J. Petrol. Sci. & Eng., 15, 101-113 (1996).

5. Schramm, L.L. and Novosad, J.J., The destabilization of foams for improved oil recovery by crude oils: Effect of the nature of the oil: J. Petrol. Sci. & Eng., 7, 77-90 (1992).

6. Rendall, A., Ayasse, C., Novosad, J., U.S. Patent 5,074,358, others pending.

7. Schramm, L.L., Ayasse, C., Mannhardt, K. and Novosad, J.J., U.S. Patent 5,301,539, U.K. Patent GB 2,271,593 B, others pending.

8. Schramm, L.L., Ayasse, C., Mannhardt, K. and Novosad, J.J., Canadian Patent 2,006,482, U.K. Patent GB 2,239,278 B, U.S. Patent 5,060,727, others pending.

Citation

This article originally appeared as: L.L. Schramm, "Foams can be effective in the presence of oil!" PetroMin, May/June, pp. 86-88, 1996.

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