Page 448 - Fundamentals of Enhanced Oil and Gas Recovery

436 Afshin Tatar

with the cell attachment. Even in case of release of dying of cells, the biopolymers
will be left behind [792].
Fractured carbonate reservoir contains most of the world’s oil [793]. In this type of
reservoirs, the matrix blocks are mixed to oil-wet. This characteristic leads to difficult
water absorption onto the matrix blocks, which in turn diminishes the sweep effi-
ciency. In fact, the oil trapped in this region will be unaffected by the floodwater
[15]. It is proved that the oil recovery can be improved by turning the matrix surface
to a more water-wet condition [16]. As it was mentioned before, this can be done by
introducing surfactants, enzymes, or development of a biofilm on the reservoir rock
surface by microorganisms. Wettability alteration plays a crucial role in oil and surfac-
tant adsorption in carbonates and clays [10]. In spite of carbonates, wettability of the
mineral surfaces plays a secondary role in oil displacement in sandstone formations.
Thus, wettability reversal by microbial activity will not provide a promising mecha-
nism for enhancing oil recovery in sandstone formations [66]. However, when the
hydrocarbon degrading microorganisms coat the oil droplets with a biofilm, the role
of wettability may become trivial [771,794]. Karimi et al. [715] through their experi-
ments concluded that the effect of biofilm formation was much more significant com-
pared with many other microbial products including biosurfactants in enhancement of
wettability. It is reported that brine composition affects the wettability changes
[795 797] (Fig. 10.8).

10.11.7 Emulsification
Microorganisms are capable to produce bioemulsifiers (high molecular weight biosur-
factants). These biochemicals create micro-emulsion in which the water is solubilized
in hydrocarbon or hydrocarbon is solubilized in water. Further details are provided in
Section 10.10.1.

Figure 10.8 MEOR by modifying the wettability [31]. MEOR, microbial enhanced oil recovery.