**2. Foam generation**

Foam generates in porous media through three different mechanisms: (a) snapoff, (b) lamella division, and (c) leave-behind [16, 17].

In the snap-off mechanism, lamellae are created in gas-filled pore throats as a result of the capillary pressure difference between the pore body and the pore neck [16]. **Figure 2a** shows the foam-generation process by the snap-off mechanism. As

**127**

**Figure 2.**

*(after [19]).*

*CO2 Foam for Enhanced Oil Recovery Applications DOI: http://dx.doi.org/10.5772/intechopen.89301*

then snap-off the gas phase.

bubbles or lamellae [18].

parallel to the flow direction [17, 18].

**3. Experimental evaluation methods**

**3.1 Bulk foam stability and microscopic analysis**

the gas phase displaces the liquid zone, the difference in capillary pressure between the pore body and the pore throat forces the wetting phase (water) to flow back and

Lamella division generally occurs when a foam lamella that is larger than that of the pore body approaches a "branching point" and divides into two or more bubbles (**Figure 2b)**. If the lamella is at a branching point with more than one path that requires the same pressure for the lamella to flow, the lamella divides into two

Leave-behind occurs when the gas enters a porous medium that is initially saturated with a liquid or when two gas fronts approach a pore space that is filled with liquid; these processes squeeze the liquid into a lamella (**Figure 2c**). The leavebehind mechanism typically forms a weak foam because the generated lamella is

Foams are generally described in terms of their foamability, which is the ability of a foaming solution (water in the presence of foaming agents) to form a foam. Bulk foam stability or formability tests are static tests that can be used for screening different parameters such as foaming agents, concentrations, salinity, and effect of crude oil [20]. At ambient conditions, foamability of a solution can be studied by performing a shake test [21]. At high-pressure/high-temperature (HP/HT) conditions, foam can be generated by gas sparging into an HP/HT

*Foam lamella generation mechanisms: (a) snap-off mechanism, (b) lamella division, and (c) leave-behind* 
