Surfactant-Stabilized Foam Stability Analysis

Three surfactants were used to perform the experiments, namely: $C_{12}$ AOS (Anionic surfactant, Alpha Olefin Sulfonate, Germany, >99.0 wt% pure), $C_{12}$ Betaine (Zwittterionic surfactant, Cocamidopropyl Betaine, Russia, >99.0 wt% pure), and FARUS (Nonionic surfactant, $C_2$ Oxyethylated phenols in monatomic alcohols, Russia,>99.0 wt% pure). In this paper, they are hereafter referred to as AOS, BETAINE and FARUS, respectively. Two binary surfactant systems were prepared from these surfactants: AOS and FARUS, hereafter referred to as AOSFAR, and BETAINE and FARUS, hereafter referred to as BETFAR. All surfactants were used as received without further treatment. The surfactant solutions were prepared in a high salinity brine (23.4 wt%) with the compositions listed in the Table 1 below. All the salt components were purchased from Chimmed, Moscow and are >99.0 wt% pure, as declared by the manufacturer.Table 1

Brine composition.

Salt	NaCl	KCl	CaCl2	MgCl2
Composition, g/L	172.056	4.261	42.172	15.7

The critical micelle concentrations of both single surfactants and their binary mixtures have been earlier determined in our previous work¹² . Thus, in this study, each surfactant was used at 1.5 times their original CMC to maximally harness their enhanced surface activity (Table 2).Table 2

Surfactant compositions and their concentrations.

Surfactant composition	Active content	Concentration, wt%
AOS - Alpha Olefin Sulfonate	35%	0.315%
FARUS - Oxyethylated phenols in monatomic alcohols	50%	0.480%
BETAINE - Cocamidopropyl betaine	75%	0.525%
AOSFAR - AOS + FARUS (1:2)	–	0.135%
BETFAR - BETAINE + FARUS (1:2)	–	0.120%

CO₂ gas with a purity of 99.98% was used to generate foam. Three mineral oils and one crude oil model were used to investigate the effect of the oil on the foam stability. The mineral oils used were n-Decane, n-Octadecane (liquid paraffin) and Toluene. The crude oil model was a sample from a producing oilfield in Russia. Their densities and molecular weights are shown in Table 3Table 3

Oil properties.

Oil	Density (g/cm3)	Molecular weight (g/mol)
Decane	0.83	142.29
Toluene	0.77	92.14
Octadecane	0.88	254.49
Crude oil	0.85	215.74

For mineral oils, 0.05 wt% of Sudan I dye was added to the oil phase to visualize the oil droplets in the foam column. Preliminary tests, including interfacial tension, density and foam columns, were performed to ensure that the dye had no influence on foaming behavior.