Page 96 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

88 Hybrid Enhanced Oil Recovery using Smart Waterflooding

surfactant EOR process are the sulfonated hydrocar- where n h is the number of hydrophilic groups; H h is the
bons such as alcohol propoxylate sulfate and alcohol value of the hydrophilic groups; n l is the number of
propoxylate sulfonate. lipophilic groups; and H l is the value of lipophilic
groups.
Hydrophile-lipophile balance
There are a number of methods to characterize surfac- Critical micelle concentration, Krafft
tants. One of the methods is the estimation of temperature, and cloud point
hydrophile-lipophile balance (HLB), which describes Another important characteristic is the critical micelle
the tendency to solubilize in oil or water. The HLB value concentration (CMC), which is defined as the concen-
indicates the tendency of surfactant to form water-in-oil tration of surfactants when the micelles spontaneously
or oil-in-water emulsion. The HLB is defined using a form. The addition of surfactant reduces the interface
couple of approaches. The studies (Graiffin, 1954; energy and removes the hydrophobic groups of the sur-
Griffin, 1949) have defined the HLB value using the factant from contact with water (Fig. 4.18A). As a result,
molecular mass of hydrophilic relative to the total mo- the free energy of the system decreases. When the surfac-
lecular mass as shown in Eq. (4.12), and the HLB value tant concentration subsequently increases in the system,
varies from 0 to 20. the surfactant molecules start to aggregate with other
molecule and micelles form (Fig. 4.18B). The formation
20MW h
HLB ¼ (4.12) of micelles sharply reduces the free energy of the system
MW
by decreasing the contact between the hydrophobic
groups of the surfactant and water, until the surfactant
where HLB indicates the value of HLB; MW h is the mo-
concentration reaches the CMC. The increasing concen-
lecular mass of the hydrophilic portion of the molecule;
tration of surfactant above the CMC results in more for-
and MW is the total molecular mass of the molecule.
mation of micelles but hardly reduces the free energy of
The zero of HLB value indicates the completely hy-
the system. Another factor to be related to CMC is Krafft
drophobic molecule of surfactant, and the value of 20
temperature or critical micelle temperature, which is
corresponds to the completely hydrophilic/lipophilic
molecule of surfactant. The other approach proposed defined as a minimum temperature where surfactants
by Davies (1957) considers the degree of the effect of can form micelles. Below the Krafft temperature condi-
hydrophilic group and defines the HLB value with Eq. tion, no micelles form regardless of the concentration of
(4.13). surfactant. The cloud point is another parameter to
illustrate the behavior of nonionic surfactant. It is
HLB ¼ 7 þ n h H h n l H l (4.13) defined as the temperature, at which the phase

FIG. 4.18 Description of distribution of surfactant molecules (A) below and (B) above CMC. (Caption: From
Sheng, J. (2011). Modern chemical enhanced oil recovery: Theory and practice. Amsterdam, Boston, MA: Gulf
Professional Pub.)