increases mobility. In surfactant flooding, surfactant reduces the IFT of injected
fluid, thus mobilization of residual oil improves oil production. In alkaline flooding,
the pH of injected fluids is increased by the addition of alkaline agents (sodium
carbonate, sodium silicate, sodium hydroxide, and potassium hydroxide) (Kumar
et al. 1989). Other than these, a binary mix of alkaline-surfactant (AS), surfactant/
polymer (SP), alkaline/polymer (AP), and alkaline/surfactant/polymer (ASP)
methods are also applied in tertiary chemical enhanced oil recovery. Combined
CEOR methods have improved efficiency for more oil production.
Other than traditional CEOR nanofluids flooding in the field has also been
evaluated by few researchers (Gbadamosi et al. 2019). Injected nanofluid contributes
to wettability alteration, IFT reduction, and improved viscosity of the injected fluid.
Nanofluid flooding can be combined with polymer flooding. Polymeric nanofluids
flooding improved rheological properties, increases stability at high temperature and
salinity conditions.
Miscible CO 2 gas injection is yet another EOR method in the tertiary oil recovery
process. CO 2 has unique displacing properties; it is due to low minimum miscibility
pressure with various types of crude oil. During CO 2 injection, it forms a singlephase fluid with hydrocarbon and disrupts the capillary effect to retaining oil in
place. CO 2 injection also promotes oil swelling, reduces fluid viscosity, and
increases oil mobility.
6.5.2 Novel Approaches for mEOR Using Toluene and Nitrate
During mEOR process, molasses and nitrate are also injected in the reservoir to
stimulate the growth of residents and introduced bacteria. Other than these, toluene
addition (light oil component) can be a good option, where toluene is present in
limiting concentration. Toluene is the preferable energy source of nitrate reducing
bacteria. Molasses is used in mEOR due to its high solubility in water and insolubility in oil, while toluene is oil soluble and low molecular weight mEOR substrate.
Hence, toluene binding to oil is prevented from been lost during water injection.
Gassara et al. (2015) investigated the effect of toluene and nitrate injection on mEOR
in laboratory scale (Gassara et al. 2015). They found that additional oil can be
produced from heavy oil containing bioreactors. In these bioreactors, they stimulated
the hNRB activity by the injection of aqueous nitrate and toluene. The mechanism
behind this lab trial is the biosurfactant and biopolymer production by microbes and
the stimulation of microbial activity by sequential addition of toluene and nitrate.
6.5.3 Polymers for Enhanced Oil Recovery
Polymer injected during polymer flooding can be categorized into two categories:
synthetic polymers and biopolymers. Synthetic polymers are polyacrylamide or its
derivatives (hydrolyzed polyacrylamide) and other copolymers of acrylamide. There
are a number of biopolymers tested for EOR efficiency such as xanthan gum,
6 Application of Biotechnology in Oil and Gas Industries
125
fluid, thus mobilization of residual oil improves oil production. In alkaline flooding,
the pH of injected fluids is increased by the addition of alkaline agents (sodium
carbonate, sodium silicate, sodium hydroxide, and potassium hydroxide) (Kumar
et al. 1989). Other than these, a binary mix of alkaline-surfactant (AS), surfactant/
polymer (SP), alkaline/polymer (AP), and alkaline/surfactant/polymer (ASP)
methods are also applied in tertiary chemical enhanced oil recovery. Combined
CEOR methods have improved efficiency for more oil production.
Other than traditional CEOR nanofluids flooding in the field has also been
evaluated by few researchers (Gbadamosi et al. 2019). Injected nanofluid contributes
to wettability alteration, IFT reduction, and improved viscosity of the injected fluid.
Nanofluid flooding can be combined with polymer flooding. Polymeric nanofluids
flooding improved rheological properties, increases stability at high temperature and
salinity conditions.
Miscible CO 2 gas injection is yet another EOR method in the tertiary oil recovery
process. CO 2 has unique displacing properties; it is due to low minimum miscibility
pressure with various types of crude oil. During CO 2 injection, it forms a singlephase fluid with hydrocarbon and disrupts the capillary effect to retaining oil in
place. CO 2 injection also promotes oil swelling, reduces fluid viscosity, and
increases oil mobility.
6.5.2 Novel Approaches for mEOR Using Toluene and Nitrate
During mEOR process, molasses and nitrate are also injected in the reservoir to
stimulate the growth of residents and introduced bacteria. Other than these, toluene
addition (light oil component) can be a good option, where toluene is present in
limiting concentration. Toluene is the preferable energy source of nitrate reducing
bacteria. Molasses is used in mEOR due to its high solubility in water and insolubility in oil, while toluene is oil soluble and low molecular weight mEOR substrate.
Hence, toluene binding to oil is prevented from been lost during water injection.
Gassara et al. (2015) investigated the effect of toluene and nitrate injection on mEOR
in laboratory scale (Gassara et al. 2015). They found that additional oil can be
produced from heavy oil containing bioreactors. In these bioreactors, they stimulated
the hNRB activity by the injection of aqueous nitrate and toluene. The mechanism
behind this lab trial is the biosurfactant and biopolymer production by microbes and
the stimulation of microbial activity by sequential addition of toluene and nitrate.
6.5.3 Polymers for Enhanced Oil Recovery
Polymer injected during polymer flooding can be categorized into two categories:
synthetic polymers and biopolymers. Synthetic polymers are polyacrylamide or its
derivatives (hydrolyzed polyacrylamide) and other copolymers of acrylamide. There
are a number of biopolymers tested for EOR efficiency such as xanthan gum,
6 Application of Biotechnology in Oil and Gas Industries
125