Page 258 - Enhanced Oil Recovery in Shale and Tight Reservoirs

240 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 9.17 Schematic of wettability alteration of an anionic surfactant in a carbonate
rock.

oil-wet as shown in Fig. 9.18 (Liu et al., 2019). Bi et al. (2004) called this
process as the first adsorption of surfactant to form a monolayer when the
cationic surfactant concentration is low. When the surfactant concentration
is high, the second adsorption takes place to form a bylayer where the
hydrophilic parts of the surfactant expose to the water phase so that the
rock becomes more water-wet.
If the siliceous surface is originally intensely occupied by negative oil com-
ponents, and cationic surfactant molecules adsorb onto the rock surface via
competition adsorption, then the rock surface is less occupied by the positively
charged oil components, probably being able to lead to less oil-wet.

9.6.5 Monolayer adsorption by nonionic surfactants
Nonionic surfactants adsorb onto rock surfaces (either carbonate or siliceous
rocks) physically by hydrophobic bonding, rather than electrostatically or
chemisorbed, forming a surfactant monolayer on the oil-wet surface. The
oil wetness may be changed to less oil-wet or intermediate-wet, as shown

Figure 9.18 Schematic of wettability alteration of a cationic surfactant in a siliceous
rock.