Foaming In situ

Foams can be generated either in situ or above ground and injected into the contaminated zone. With in situ foam generation, no volatile organic compounds would be created. 

Extensive mobility control applications of foams are limited by inadequate knowledge of foam displacement in porous media, plus uncertainties in the control of foam injection. Because of the importance of in situ foam texture (bubble size, bubble size distribution, bubble train length, etc.), conventional fractional flow approaches where the phase mobilities are represented in terms of phase saturations are not sufficient. As yet, an adequate description of foam displacement mechanisms and behavior is lacking, as well as a basis for understanding the various, often contradictory, macroscopic core flood observations. 

Equation 53 has the same general form as Equations 44 and 49. At this point, K3 and n must be considered as empirical parameters which will be dependent on the in situ foam texture, gas saturation, and the porous medium structure. 

The liquid saturations in foam flow are typically close to irreducible liquid saturation. As a result, the liquid saturation in a foam filled medium is generally not a good measure of the quality of the in situ foam, but rather the fraction of pore segments completely filled with liquid. More permeable media, such as unconsolidated media, generally have smaller residual liquid saturations (32,33) and thus tend to have higher gas saturations when foam is flowing. 

Although the current permeability model properly reflects many of the important features of foam displacement, the authors acknowledge its limitations in several respects. First, the open pore, constricted tube, network model is an oversimplification of true 3-D porous structures. Even though communication was allowed between adjacent pore channels, the dissipation associated with transverse motions was not considered. Further, the actual local displacement events are highly transient with the bubble trains moving in channels considerably more complex than those used here. Also, the foam texture has been taken as fixed the important effects of gas and liquid rates, displacement history, pore structure, and foam stability on in situ foam texture were not considered. Finally, the use of the permeability model for quantitative predictions would require the apriori specification of fc, the fraction of Da channels containing flowing foam, which at present is not possible. Obviously, such limitations and factors must be addressed in future studies if a more complete description of foam flow and displacement is to be realized. 

Tertiary oil was increased up to 41% over conventional CO2 recovery by means of mobility control where a carefully selected surfactant structure was used to form an in situ foam. Linear flow oil displacement tests were performed for both miscible and immiscible floods. Mobility control was achieved without detracting from the C02-oil interaction that enhances recovery. Surfactant selection is critical in maximizing performance. Several tests were combined for surfactant screening, included were foam tests, dynamic flow tests through a porous bed pack and oil displacement tests. Ethoxylated aliphatic alcohols, their sulfate derivatives and ethylene oxide - propylene oxide copolymers were the best performers in oil reservoir brines. One sulfonate surfactant also proved to be effective especially in low salinity injection fluid. 

Apparatus and Procedure. It was necessary to design more definitive tests to further evaluate the better candidate surfactants. This was accomplished by means of a multi-phase dynamic-fiow test that consists of a small packed bed through which surfactant solution can be passed followed by gas to produce in situ foam. The pressure drop through the column is measured as the fiuid is drawn through the column at a constant volumetric fiow rate. From the recorded data, relative mobilities of the liquid and gas phases may be calculated. The change in gas mobility due to the presence of the surfactant is very closely related to the effectiveness of that surfactant for mobility control in oil core studies. A schematic drawing of the apparatus is shown in Figure 2. 

His research interests have included many aspects of colloid and interface science applied to the petroleum industry, including research into mechanisms of processes for the improved recovery of light, heavy, or bituminous crude oils, such as in situ foam, polymer or surfactant flooding, and surface hot water flotation from oil sands. These mostly experimental investigations have involved the formation and stability of dispersions (foams, emulsions, and suspensions) and their flow properties, elec-trokinetic properties, interfacial properties, phase attachments, and the reactions and interactions of surfactants in solution. 

It may happen that a foam that is desirable in one part of the oil production process may be undesirable at the next stage. For example, in the oil fields, an in situ foam that is purposely created in a reservoir to increase viscosity (and thereby improve volumetric sweep efficiency as part of an oil recovery process) may present a handling problem when produced. 

Foam Flooding Processes If the injection of the surfactant solution is followed by gas injection, it can form in-situ foam, which can improve oil recovery. Several aspects of foam flooding such as mechanism of foam flow in a porous medium, microscopic behavior of foam, bubble size, CO2 foam, steam foam and oil recovery have been discussed in the literature.Several aspects of the foam flooding process are schematically presented in Figure 7. 

The effect of oil viscosity on the displacement of oil is presented in Figure 10. In order to determine the oil displacement efficiency by foam flooding, the injection of gas phase was started at surfactant solution breakthrough. Both air and steam were employed to generate in-situ foams. The steam foam recovered more oil as compared to air foams. 

Surfactants play an important role in the formation and stability of foams. Investigators have determined foam stability by measuring the half-life (e.g. t 2) the foam. Half-life is the time required to reduce foam voLume to half of its initial value. It has been demonstrated that the foam stability (i.e.half-life) decreased with increasing temperature, whereas the foaminess of the surfactant solution increased with temperature. It is likely that these properties of foam depend on the molecular structure and concentration of the surfactant at the gas/liquid interface. Comparison of the results of static foam stability with that of the dynamic behavior of foam in porous media revealed that the foam stability is not required for efficient fluid displacement or a decrease in the effective air mc >ility in a porous medium. Moreover, the ability of the surfactants to produce in-situ foam was one of the important factors in the displacement of the fluid in a porous medium. 

It can be anticipated that all gas-flood projects, as they are presently being carried out, will leave a large fraction of the reservoir oil uncontacted by the injected fluids. This bypassed oil will remain inplace, undisplaced by the injected fluid. Thus, in each current field project, the amount of incremental oil produced by gas flooding could be substantially increased if the uncontacted oil could be reached. The improvement of the vertical and areal distribution of injected fluids through-out the reservoir requires much better methods of sweep and mobility control. The utility of the foams, in general, as mobility control agents has not been extensively tested. In principle they offer a spectrum of fluid mobility behaviour depending on the in-situ foam phase stability. 

Another commonly used technique is to use in situ foaming of e.g. poly(urethane) (PU) (21). However, PU is not considered as... 

Core materials and sandwich plies must be placed on to an adequate layer of resin and then firmly and evenly weighted to ensure full contact with the outer skin until bonded. Care needs to be taken to provide escape routes for entrapped air. They may be held against the wet resin by using a vacuum or pressure bag, press or autoclave instead of weights—this is a very efficient method. In situ foaming of core material can be used instead of ready foamed slabs, especially on difficult curves or for gap filling. 

In-situ foaming (i)in- sl-(i)tu [L, in position] (1740) adv, adj. The technique of depositing a foamable plastic (prior to foaming) into the volume where it is intended that foaming shall occur. An example is the placing of foamable plastics into cavity brickwork to provide insulation. Shortly after being poured, the liquid mix foams and fills the cavity. 

In situ foaming is an another typical on-site application used mainly for insulation purposes. Since rigid PU and polyisocyanurate foams provide the most energy efficient and versatile thermal insulations, they are preferable for use in roof and wall system applications, for both residential and commercial buildings. 

Bernal, M. M., M. A. Lopez-Manchado, and R. Verdejo. 2011. In situ foaming evolution of flexible polyurethane foam nanocomposites. Macrom. Chem. Phys. 212 971-979. 

To understand the inorganic foam formation as a function of silica fume constant, some experiments were performed (Figure 5). The F, sample was characteristic of the first in-situ foam synthesized (Table 1). The ratio of the final volume to initial volume was given to compare the influence of components depending on the molar ratio. The increase of the final volume in relation to the amount of silica fume revealed the important role of this compound for in-situ inorganic foam formation. Nevertheless, the amount of silica fume must be at least 50 wt. % to get a significantly porous material. For higher values, the volume enhancement was proportional to the silica amount and corresponded to an initial molar ratio of ns /nK = 2.5. 

Urea-formaldehyde (UF) foams are available in densities ranging from 80-160 kg/m both as in situ foams or preshaped. They have a narrow working range of temperature 243K ( 30°C) to 320K (47°C). In addition, the foams readily absorb a variety of liquids including water. This leads to one important application—cut flower arrangements UF foam of low density is easily pierced by the stems of flowers and the foam will absorb sufficient water to keep the flowers fresh for several days. 

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