**3.1 Bulk foam stability and microscopic analysis**

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

**Figure 2.**

*Foam lamella generation mechanisms: (a) snap-off mechanism, (b) lamella division, and (c) leave-behind (after [19]).*

visual graduated cell [22, 23]. The foam half-life time can be measured by monitoring the foam height over time.

Additionally, bubble-scale experiments can be conducted under an optical microscope to investigate the foam stability [24]. The foam bubbles are allowed to stabilize and are then placed on a microscope slide. The foam texture and the thin liquid films (lamellae) are then monitored with time to investigate the foam decay rate [23]. **Figure 3** shows a microscopic image for an AOS foam system in contact with a crude oil.
