This large quantity is generally drawn from nearby water aquifers (e.g., sea, river,
and lake or ponds) and sewage treatment plants. Besides, the onshore oil fields adopt
a sustainable process, produced water re-injection (PWRI), wherein the produced
water after oil separation is reused for re-injection in oil field. The offshore oil fields,
on the other hand, have access to large sums of sea water, and, therefore, do not
require PWRI strategies (Prajapat et al. 2019).
6.2
Microbiology of Oil and Gas Industry
Microbes are ubiquitous in nature and are present in a variety of extreme
environments. However, earlier beliefs added oil and gas industries as an exception,
till the nineteenth century, when the microbiology of oil reservoirs was introduced
(Bastin et al. 1926). It was found that the oil reservoir heterogeneous nature itself
provides different extreme environments such as high pressure, temperature, salinity, and depth barriers for the growth of organisms. There are varied microbial
communities thriving in different oil reservoir zones. Some of these communities
are sulfate reducing bacteria (SRB), fermentative bacteria, nitrate reducing bacteria
(NRB), iron reducing bacteria (IRB), iron oxidizing bacteria (IOB), and
methanogens. These bacterial groups are known to perform their metabolism
based on different hydrocarbon sources. Hydrocarbons or oil organics present in
the reservoir act as energy sources for these microorganisms with inorganic
molecules as an electron acceptor.
Among the different microbial communities, SRB are known to be the dominant
species present in the oil fields (Voordouw et al. 1996). Many studies have also
stated, they are indigenous to the oil reservoir (Stetter et al. 1987), however,
controversies exist whether SRB are indigenous to oil fields or are been introduced
with injection water. Though, the existence of similarities between the oil field and
hydrothermal SRB population shows the mobility/transportation of SRB
communities between two geological distinct environments (Stetter et al. 1987;
Voordouw et al. 1996). SRB communities are further known to belong to both
eubacterial and archeal lineages. Besides SRB population two different types of
NRB are present in the oil reservoir, i.e., heterotrophic nitrate reducing bacteria
(hNRB) and sulfide oxidizing nitrate reducing bacteria (so-NRB). The hNRB are
known to perform dissimilatory heterotrophic nitrate reduction (into N 2 or ammonia)
with the oxidation of oil organics, while so-NRB reduce nitrate into N 2 or ammonia
with the oxidation of sulfide into elemental sulfur or sulfate. The NRB abundance is
privileged when the nitrate is injected in the reservoir in order to control microbial
souring.
The iron reducing bacteria (IRB) and oxidizing bacteria (IOB) are yet other
dominant bacterial groups present in various oil fields setup. Iron reducing bacteria
uses ferric iron as a terminal electron acceptor, while iron oxidizing bacteria are
found to oxidize the ferrous ions. Additionally, IOB are known to oxidize the Fe
under different set of conditions, e.g., acidic, neutral pH, phototrophically, anaerobically, autotrophically, and heterotrophically (Ionescu et al. 2015).
6 Application of Biotechnology in Oil and Gas Industries
115
and lake or ponds) and sewage treatment plants. Besides, the onshore oil fields adopt
a sustainable process, produced water re-injection (PWRI), wherein the produced
water after oil separation is reused for re-injection in oil field. The offshore oil fields,
on the other hand, have access to large sums of sea water, and, therefore, do not
require PWRI strategies (Prajapat et al. 2019).
6.2
Microbiology of Oil and Gas Industry
Microbes are ubiquitous in nature and are present in a variety of extreme
environments. However, earlier beliefs added oil and gas industries as an exception,
till the nineteenth century, when the microbiology of oil reservoirs was introduced
(Bastin et al. 1926). It was found that the oil reservoir heterogeneous nature itself
provides different extreme environments such as high pressure, temperature, salinity, and depth barriers for the growth of organisms. There are varied microbial
communities thriving in different oil reservoir zones. Some of these communities
are sulfate reducing bacteria (SRB), fermentative bacteria, nitrate reducing bacteria
(NRB), iron reducing bacteria (IRB), iron oxidizing bacteria (IOB), and
methanogens. These bacterial groups are known to perform their metabolism
based on different hydrocarbon sources. Hydrocarbons or oil organics present in
the reservoir act as energy sources for these microorganisms with inorganic
molecules as an electron acceptor.
Among the different microbial communities, SRB are known to be the dominant
species present in the oil fields (Voordouw et al. 1996). Many studies have also
stated, they are indigenous to the oil reservoir (Stetter et al. 1987), however,
controversies exist whether SRB are indigenous to oil fields or are been introduced
with injection water. Though, the existence of similarities between the oil field and
hydrothermal SRB population shows the mobility/transportation of SRB
communities between two geological distinct environments (Stetter et al. 1987;
Voordouw et al. 1996). SRB communities are further known to belong to both
eubacterial and archeal lineages. Besides SRB population two different types of
NRB are present in the oil reservoir, i.e., heterotrophic nitrate reducing bacteria
(hNRB) and sulfide oxidizing nitrate reducing bacteria (so-NRB). The hNRB are
known to perform dissimilatory heterotrophic nitrate reduction (into N 2 or ammonia)
with the oxidation of oil organics, while so-NRB reduce nitrate into N 2 or ammonia
with the oxidation of sulfide into elemental sulfur or sulfate. The NRB abundance is
privileged when the nitrate is injected in the reservoir in order to control microbial
souring.
The iron reducing bacteria (IRB) and oxidizing bacteria (IOB) are yet other
dominant bacterial groups present in various oil fields setup. Iron reducing bacteria
uses ferric iron as a terminal electron acceptor, while iron oxidizing bacteria are
found to oxidize the ferrous ions. Additionally, IOB are known to oxidize the Fe
under different set of conditions, e.g., acidic, neutral pH, phototrophically, anaerobically, autotrophically, and heterotrophically (Ionescu et al. 2015).
6 Application of Biotechnology in Oil and Gas Industries
115