Page 477 - Fundamentals of Enhanced Oil and Gas Recovery

Microbial Enhanced Oil Recovery: Microbiology and Fundamentals 465

A new concept in MEOR is to employ the enzymes to enhance oil recovery.
Generally speaking, addition of enzymes to the waterflood can enhance oil recovery
from both sandstone and carbonate cores [60]. Enzymes are a specific group of pro-
teins synthesized by living cells capable to catalyze several biochemical reactions [947].
As the catalysts, enzymes reduce the activation energy of a reaction and consequently
significantly enhance the rate of the reaction [948,949]. Enzymes can either degrade
the unwanted chemicals or generate the desired ones [946]. Some enzymes having
potential for enhancing oil recovery are [60]:
1. Greenzyme, which is a commercial EOR enzyme and consists of enzymes and sta-
bilizers (surfactants),
2. The Zonase group consists of two types of pure enzymes, Zonase1 and Zonase2,
which are protease enzymes and whose catalytic functions are to hydrolyze (break-
down) peptide bonds,
3. The Novozyme group consists of three types of pure enzymes, NZ2, NZ3 and
NZ6, which are esterase enzymes and whose catalytic functions are to hydrolyze
ester bonds, and
4. Alpha-lactalbumin, which is an important whey protein.
The main processes, aiding the enzyme enhanced oil recovery are the adsorption
ability of enzymes 2 proteins as well the accompanying increase in the water-wetness
[950]. Enzymes 2 proteins can improve the waterflooding efficiency by converting the
wettability to a more water-wet condition, especially in oil-wet reservoirs
[60,951,952]. Enzymes can amend the fluids 2 rock interfacial dynamics and influence
the wettability and capillary action and also make emulsions, which can promote oil
recovery [60,953]. Moreover, enzymes can improve the plugging methods by degrad-
ing the insoluble bacterial cells resulted from the fermentation process and also molec-
ular aggregates or micro-gels for improving the injection efficiency of biopolymers
[954]. The generated products during the catalyzed reactions can promote the plug-
ging efficiency, thus, enzymes can be used to modify the reservoir permeability profile
too [955]. Several authors have proposed the application of enzymes to modify the
permeability profile of the porous media in conventional and fractures reservoirs
[955,956]. Nemati and Voordouw [955] successfully utilized enzymes to catalyze a
CaCO 3 formation to reduce the porous media permeability. It is proved that several
hydrolases (the enzymes, which catalyze the hydrolysis of a chemical bond) can break
down the crude oil components [60]. For example, hydrolase enzymes catalyze the
bond cleavage via introduction of water, which may break down the crude oil com-
ponents into either smaller molecules with increased water solubility and reduced
interfacial activity or more polar molecules such as hydrolyzing ester to form acid and
alcohol [60]. The mentioned process may affect the wettability and IFT (see
Fig. 10.9). It is worthwhile to mention that Khusainova [957] specified that crude oil
may contain esters in the form of either free compound such as dioctylphthalate [958]