A Pore-Level Investigation of Foam/Oil Interactions in Porous Media
- David J. Manlowe (U. of California) | Clayton J. Radke (U. of California)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- November 1990
- Document Type
- Journal Paper
- 495 - 502
- 1990. Society of Petroleum Engineers
- 5.4.6 Thermal Methods, 5.1 Reservoir Characterisation, 4.1.2 Separation and Treating, 5.4 Enhanced Recovery, 1.6.9 Coring, Fishing, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.1.5 Processing Equipment, 5.3.4 Reduction of Residual Oil Saturation, 4.3.4 Scale
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Direct visual studies of foam flow in etched-glass micromodels containing residual oil demonstrate that foam decays as a result of breakage of pseudoemulsion films. Foam films collapse whenever nearby thin aqueous films separating gas bubbles and oil rupture. Consequently, surfactant formulation for foam insensitivity to oil in porous media should be based on stabilizing pseudo-emulsion films.
Recently, use of foam as a mobility-control agent in EOR has shown success in steamflooding field applications. Foam has the unique attribute of exhibiting apparent viscosities up to 1,000 times greater than its constituent phases: liquid and gas. To achieve and maintain mobility control in oil reservoirs, the foam should remain stable against collapse. Unfortunately, oil deleteriously affects the stability of foam, which has obvious ramifications for the use of foam in EOR.
For the most part, foam/oil interactions in porous media have been characterized by studies on bulk foams. Typically, different variants of the common shake test are used in which surfactant solution, air, and oil are mixed to produce a foam, after which the decay of foam height is measured over time. The rate at which the foam height decays is thought to be a measure of the ability of the surfactant to produce and stabilize foam in the presence of the sample oil. This result may indeed be valid for bulk foams. However, direct application to foams in porous media is suspect. The type of foam present in a shake test may be radically different from that in porous present in a shake test may be radically different from that in porous media, especially with regard to the foam structure, the thickness of the lamellae, and the processes by which the foam collapses. Nevertheless, the shake test is commonly used to screen surfactants for use in steam and CO2 floods.
Assessing the mechanistic interactions of foam and oil in porous media demands studies other than those on bulk foam outside the medium. Foam confined in a porous medium is different from bulk foam. To date, the only method used to study foam stability against oil in porous media is to measure indirect properties such as pressure drops and foam-propagation rates across a core. Unfortunately, these secondary diagnoses have limited value for revealing the relevant interactions between foam and oil.
The objective of this work is to determine directly the mechanism(s) by which oil destabilizes foam in porous media. We visually studied foam in an etched-glass, porous-medium micromodel containing residual oil. The ability to create and analyze the foam in a transparent, prototype porous medium avoids the pitfalls of correlating results from bulk foam and secondary parameter studies and provides pore-level information on actual destabilizing events.
Previous Work Previous Work The strong destabilizing effect of crude oil on foam was first emphasized in the context of porous media by Bernard and Holm. They reported that foam's effectiveness in reducing gas mobility greatly diminished when crude oil was present.
More recently, Lau and O'Brien studied oil/foam interactions in laboratory sandpacks 90 % saturated with oil at ambient temperature and pressure. The surfactant solution was a 0.5 wt% solution of Siponate DS-10 (a branched-side-chain dodecylbenzene sodium sulfonate) in 1.2 wt% NaCl. They selected oils that did not scavenge surfactant or form macroemulsions: hexadecane and a 30/70 mixture of Nujol and Shell-Sol 71. Surface tension and interfacial tension (IFT) measurements between the phases revealed spreading coefficients of 1.8 and -0.8 mN/m for hexadecane (spreading oil) and for the Nujol mixture (nonspreading oil), respectively.
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