Page 304 - Fundamentals of Enhanced Oil and Gas Recovery

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10.2 DEFINITION

Microbial enhanced oil recovery (MEOR) is one of the tertiary oil recovery
categories. Any process utilizing microorganisms and/or their metabolic products
including biosurfactants, biomass, biopolymers, bioacids, biosolvents, biogases, and
also enzymes to improve the petroleum production from marginal or depleted reser-
voirs is referred to as MEOR [7,15 19]. This would improve the life of the oil wells.
Microbes are single-celled organisms existing everywhere in the nature, including the
hydrocarbon reservoirs [15,20] having a substantial impression on the reservoir geo-
chemistry and behavior as well as oil mobilization [10,21]. The microbes utilized in
MEOR are typically nonpathogenic hydrocarbon-utilizing microorganisms [22]. The
bioproducts generated by the microorganisms amend the physical-chemical properties
and consequently the oil 2 water 2 rock interaction to enhance oil recovery [22].
Microorganisms can also be employed to clean up the wellbore and remove the built-
up hydrocarbons. Although this would promote the well injectivity as well as the flow
out of the well, this is not categorized as MEOR. MEOR applies biotechnology to
enhance the oil recovery. Despite other tertiary recovery methods, there has not been
great attention regarding this method. However, numerous experimental studies has
proved that certain microorganisms are capable to develop under the high pressure,
temperature, and salinity condition of underground reservoir and produce metabolic
products such as biosurfactants, biopolymers, alcohols, acids, and gases. The men-
tioned compounds can displace the trapped oil via several mechanisms, which will be
discussed in the following sections. The combination of multiple mechanisms, which
work simultaneously, makes this method highly effective.
MEOR may receive especial attention due to its cost advantage over the synthetic
surfactants. Several tertiary oil recovery techniques such as steam flooding, polymer
flooding, chemical surfactant flooding, and in-situ combustion have been found to be
complex or induce heavy costs to be applicable for extensive utilization [23]. The
main expenditures of Enhanced Oil Recovery (EOR) projects are related with pro-
duction and transportation of EOR chemicals. In case of in situ production of EOR
chemicals, at the oil droplet, the costs will significantly reduce [10]. MEOR does not
require exceptional investments [23]. It is possible to use the existing waterflooding
facilities and equipment with minor modification in this regard [24]. Although the
microbes require plentiful nutrients to grow and develop, these nutrients are quite
cheap, thus the MEOR technique relatively costs less [25 27]. Fig. 10.1 shows the
incremental cost per barrel for various different EOR techniques. Microbial growth
takes place at exponential rates [28,29]. This may make it possible to rapidly generate
the desired bioproducts from cheap and renewable resources [6]. Moreover, the meta-
bolic generated biochemicals are independent of the crude price, whereas most of