Foams gelled

In the case of flexible foams, gelling usually occurs before rise and tack-free times come after rise is completed. In contrast, tack-free times of rigid urethane foams sometimes are needed before rise is completed, although they are usually reached after rise. 

Foamed stability afreets add-etched fradure flow capacity in the same way that it affects fluid loss control. By indeasing foam stability, a substantial indease in fradure flow condudivity will occur. By indeasing the foam stability, the pattern of rock removal is more effedive without overetching the fradure face (30). Using lower quality foams, gelling the reaction phase and indeasing the viscosity of the foam achieve maximum fracture flow capacity. 

To a foamed gelling hydrocolloid system a firming agent and a fibrous material are advantageously added. When articles prepared from such compositions are coated with a suitable coating, they are impervious to boiling water and able to withstand microwave heating (33). 

Examples for the foamed gelling hydrocoUoid system are summarized in Table 7.7. 

Polyurethane is pulverized to iacrease its bulk density, mixed with 30—80% of a thermoplastic mol ding material, gelled, and then granulated to give coated urethane foam particles 0.1 to 0.15 mm in size (48). The particle bulk density is three times that of the polyurethane, while the volume is 15% less. This material may be injection molded or extmsion molded into products (49). Other technologies for recycling polyurethanes have also been reported. 

Catalysis of the flexible polyurethane foaming operation is accompHshed through the use of tertiary amine compounds, often using two different amines to balance the blowing and gelling reactions. OrganometalHc compounds, usually staimous salts, are also used to faciHtate gelling and promote final cure. 

Box Foa.ms. A measured quantity of the reaction mixture can be placed ia an open-topped crate or box and allowed to foam ia a free rise mode. The block is removed after gelling and is cut iato end use pieces after curiag. 

After the compound is prepared, it is whipped either on a batch or continuous basis. The Oakes continuous mixer is the standard piece of equipment ia the iadustry. Then the gelling agents, ie, Na2SiFg and ZnO, are added, the foam poured iato molds and cured, and the product stripped from the mold for further cure. 

In the Talalay process, the froth is produced by chemical rather than mechanical means. Hydrogen peroxide and an enzyme decomposition catalyst are mixed iato the latex and the mixture placed ia the mold. Decomposition of the peroxide by the added enzyme results ia the Hberation of oxygen which causes the latex mix to foam and fill the mold. The foam is then rapidly chilled and CO2 is iatroduced to gel the latex. The gelled foam is then handled ia a manner similar to that used ia the Dunlop process. 

Carrageenan is a gelling agent that forms a complex with the milk proteins, adding bulk and strength. A small amount will make a large difference in the ability to hold air in the foam. 

Gelatin has long been used as a food ingredient (e.g., gelling and foaming agent), in the preparation of pharmaceutical products (e.g., soft and hard capsule, microspheres), in the... 

In the case of aerated protein icings, however, stabilizers are essential. Where hot water is used, gelling-type stabilizers work best (agar, gelatin, Irish moss extract). In cold foams, prepared with cold water, cellulose-type gums are used to contain water in the foams colloidal precipitates, such as are formed through the reaction of carrageenin and protein, are very helpful. 

Certainly the optimal techniques depend on the type of reservoir. Reports that compare the techniques in a related environment are available. In the Kansas Hugoton field (Mesa Limited Partnership), several hydraulic fracturing methods were tested [403]. A method in which a complexed gelled water fracture was applied was the most successful when compared with a foam technique and with older and simpler techniques. The study covers some 56 wells where such techniques were applied. 

Incomplete texturization or partial denaturation at temperatures below 60 °C significantly increased gel strength, but at 75 °C or above, complete loss of the gelling property resulted. Foam volume remained high up to 50 °C but decreased significantly (p < 0.05) above 75 °C. Foam stability followed the same pattern as foam volume, being very stable for an hour below 50 °C. On the contrary, Phillips et al. (1990) reported that WPI heated to 80 °C had little effect on foam stability. 

Carico(139-140) has published comparative information about the various gelling agents. Xanthan has been adapted to foam fracturing gels. Xanthan gels can be broken by the addition of lithium hypochlorite(141). 

Distinctly different approaches to avoid these problems and still achieve high viscosities were conceived and applied. The different approaches can be categorized as 1) preparation of emulsions or foams and 2) addition of crosslinkers to the polymer. Two separate processes which utilized crosslinking of polymer gelling agents were pursued. These are the use of secondary (or delayed) gelling agents and the use of metallic crosslinkers added on-site. 

Emulsions. Emulsion fluids and foams came into routine use in competition with crosslinked fluids during 1970-80. Simple, barely stable emulsions had been used early in fracturing. These were mainly emulsified acids that "broke" when the acid spent on the formation surfaces. In the late 1960 s Kiel became a proponent of very high viscosity oil fluids as a method to place exceptional (at the time) amounts of proppant(337,338). To avoid the frictional resistance typical of gelled oils he advanced the concept of preparing a very viscous oil-external emulsion with one part fresh water, 0.1% sodium tallate surfactant, and two parts oil. The viscous emulsion had to be pumped simultaneously with a water stream to minimize frictional pressure. This process was clumsy and still... 

A method of manufacturing latex foam. Compounded latex is foamed and gelling agent added the mould is filled and the gelled foam vulcanised by steam at 100 °C the product is stripped from the mould, washed and dried. See Talalay Process. 

The gelling agent used in the manufacture of latex foam by the Dunlop process. 

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