Flow Behavior of Foam: A Porous Micromodel Study
- Owete S. Owete (Stanford U. Petroleum Research Inst.) | William E. Brigham (Stanford U. Petroleum Research Inst.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- August 1987
- Document Type
- Journal Paper
- 315 - 323
- 1987. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 5.7.2 Recovery Factors, 5.1 Reservoir Characterisation, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.3.4 Scale, 1.2.3 Rock properties, 4.1.5 Processing Equipment, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.4.3 Sand/Solids Control, 5.4 Enhanced Recovery
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Summary. The flow behavior of foam in porous micromodels has been studied visually by use of etched silicon wafers. Air was injected into homogeneous and heterogeneous porous media previously filled with an aqueous surfactant solution. The flow characteristics and the mobility of the injected air were determined under different conditions of pore dimensions, air injection rates, and surfactant concentrations.
In the experiments, air was found to be propagated by displacement of lamellae in long bubbles flowing and extending across several pore lengths, while the liquid flowed through the network of films. Propagation of foam bubbles formed at pore constrictions by snap-off was dominant in the heterogeneous model. Liquid and/or gas was trapped in some pores. The mechanisms observed depended on pore structure and surfactant concentration. A considerable reduction of effective air mobility was observed in the presence of foam. Mobility reduction depended on flow mechanisms.
Foam has been proposed as a mobility control agent under the assumption that foam reduces the gas mobility and that this reduction is proportionately higher in morepermeable sands. Previous studies attempted to explain how foam and its components are propagated through a network of pores.
Fried, Marsden and Khan, Raza and Marsden, and David and Marsden proposed the homogeneous fluid flow mechanism. Foam flows as a body; the gas and liquid flow at the same rate, and the foam behaves as a single fluid with high apparent viscosity. The work of Bernard et al, Holm, and Mast indicates that the gas component of foam flows through porous media by breaking and reforming films, while the liquid is transported as a free phase through the film network. Bernard and Holm, Marsden and Khan, and Nahid also suggest that the liquid flow could be treated according to Darcy's law. Work by Kolb, to Nahid, and Mast suggests that a portion of either gas or liquid or both is trapped in the porous medium, while the flowing phases flow according to Darcy's law.
None of these mechanisms fully explains all the observed flow properties of foam, and there is no generally accepted theory stating when a given mechanism is dominant. Researchers generally agree, however, that foam impedes the flow of gas in porous media. Most of the work already cited and the studies by Raza and Holcomb et al indicate that foamer concentration, pore structure, and flow rate, among other factors, influence the behavior of gas in the presence of foam. One problem with many foam experiments is that they are conducted in systems that do not allow direct observations of foam generation and propagation. Thus our objective was to make a visual study of the flow mechanisms of foam and its components in micromodels of differing pore structure and dimensions.
Fig. 1 is a schematic of the apparatus. A low-rate syringe pump injected fluid (water, surfactant solution, or air) into the micromodel. The pump advanced a piston at a constant rate. The actual input rate of injected air must be calculated, taking into consideration the compressibility of the air, the varying injection pressure, and the constant rate of the syringe piston. The outlet pressure was at atmospheric pressure, and the pressure drop across the model was monitored with two differential transducers connected in parallel.
An observation system was used to view and to document the flow of fluids in the micromodel. The upper half of Fig. 1 shows the spatial arrangement of the major components: an illuminator, a cycloptic microscope, a dualobservation system, a photographic assembly, and a video monitor and recorder. Two cameras, a 35-mm camera and a video TV camera, were mounted on the photographic tube adapters. A black-and-white 9-in. [23-cm] diagonal video monitor was connected to the input of a VHS video recorder. The linear magnification of this system depends on the objective eyepiece combination and the setting of the magnification-changer attachment. Typically, the system view field ranged from 0.03 x0.03 to 0.13 x0. 13 in. [0.7x0.7 to 3.2x3.2 mm].
In this study, we used two types of micromodels: those with homogeneous and those with heterogeneous pore structures. Each model consisted of an etched silicon wafer on which a monolayer of porous matrix was simulated. A layer of silicon dioxide was thermally grown on the silicon wafer to achieve a wettability similar to that of natural porous media.
Fig. 2, drawn to scale, shows the fluid flow area of the micromodel. The large central area, aXd, of the figure is a network of etched flow channels. The flow channels interconnect a system of unetched solid matrix.
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