Block foaming

Rigid and flexible polyurethane foams often utilize fire-retardant chemicals. For flexible foams, pentabromodiphenyl ether (now banned in Europe) is used, particularly to avoid the problem of scorch (yellowing of the inside of the block foam), which is most prevalent in hot, humid conditions. Tribromoneopentyl alcohol, which reacts into the urethane polymer, is also used. Brominated... 

The continuous loaf of foam made by the continuous pouring of liquid foaming components on a moving conveyor is called a slabstock foam, and a cut-off segment of the slabstock is called block foam or bun foam. The horizontal-conveyer process has been used widely since the beginning of the urethane foam industry. Recently, however, vertical production processes have been developed. 

Preparation. Urethane-modified isocyanurate foams are mostly fH epared by the one-shot process based on the jH inciple discussed previously in the urethane modification section. The semi-prepolymer process is used only in limited cases because of viscosity problems. This section describes several examples of formulations for producing block foams, slabstock foams, laminate foams, and spray foams. 

In the case of box foaming, the foam in a box must be kept in the box for post curing at room temperature. If the box foam is taken out immediately after foaming, many cracks may be formed. The same attention must be paid to bun foam (block foam). These foams must be post cured at ambient temperature, either by indoor or outdoor curing for at least a week. 

Foaming Process of Resol-Type Foam. The foaming processes for phenolic foam of both the resol type and benzylic-ether type are the same as those for rigid polyurethane foams. The block-foaming process (slab foaming), pouring process, continuous-laminate process, and spray process are used. See Figure 57. 

Table 66 General Properties of Resol-Type Foam Prepared by the Block Foaming Process (12)...

From the known practical benefits to such wells of geological barriers, it was envisaged that foam could be effective as a means of reducing gas coning if it could be made to form an in situ barrier between the oil and the gas cap. Experiments were designed to test the creation of a barrier of gas-blocking foam and measure its effect on production using sector models. 

Table L Sector Model Experiments Used To Study Gas-Blocking Foam Barriers...

Generation of a barrier of gas-blocking foam was accomplished by returning the sector model to production after a horizontal surfactant solution layer was in place. First, a cone of colored surfactant solution formed and excess injectant was produced back. Subsequent downward movement of gas was significantly delayed by the formation of a foam front trailing the surfactant cone. After some time, a foam cone having essentially the same shape as the previously observed gas cone formed, and gas breakthrough was delayed or hardly noticeable. Production rates could now be increased to provide, in Model 1, oil rates of 8 to 10 cm3/min (6—8 times the critical rate) with no or very low production of associated gas. 

Figure 3. Measured, production in sector models with gas coning in the absence and presence of barriers of gas-blocking foam.

Figure 4. Generation of gas-blocking foam in vertical 2-m long packs of 8-darcy glass beads. Volume of surfactant slug not to scale.

Figure 5. Generic apparatus used for studying gas-blocking foams. (Reproduced with permission from reference 13. Copyright 1993.)...

Oil. As for other applications of foam in porous media, the presence of oil is also important to gas-blocking foams because it may impair the ability of foam to reduce gas mobility in situ. A foam to be used in blocking gas around an oil well must withstand prolonged exposure to oil and should thus be intrinsically oil tolerant. This necessity is in contrast to other applications where dynamic metastability of the foam has been claimed to be sufficient because the foam is assumed to flow through the pores and will have its lamellae in contact with oil for only brief periods (30). Oil—foam interaction has been a main focus of our work on aqueous gas-blocking foams and is published separately. In the present context, however, because the topic is reviewed elsewhere in this book, only the main conclusions are given. 

Foam studies should not be done at atmospheric outlet pressure (37) because this introduces bubble expansion effects. We have found unpredictable differences between gas-blocking foams generated at atmospheric outlet pressure and outlet pressures of 5-6 bar (13). All our subsequent foam performance tests have been conducted at an elevated back pressure, even if reservoir conditions are not desired. We also attempt to limit the ratio between pressure drop and overall pressure, AP/P, to less than 20%... 

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