Page 452 - Fundamentals of Enhanced Oil and Gas Recovery

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If the microorganisms needed to perform specific metabolisms are absent, injection of
microorganisms along with the nutrients is the alternative. It would be difficult for
the exogenous microorganisms to establish themselves over the indigenous ones. As
the supplied nutrients may stimulate the detrimental microbial activities such as sour-
ing and corrosion, extreme caution should be considered [17].
The oil fields worldwide exhibit complicated biological systems, the exact replica-
tion of which in laboratory is very challenging [15]. Maudgalya et al. [23], after
reviewing several field trials, stated that in most of the cases the laboratory results can-
not be replicated by the field trials. As an example, the performance of the
lipopeptide-producing Bacillus strain JF-2 [806] was tested in both laboratory core
flood and field [88,687] and the results were inconsistent. Emerge of new advanced
technology will provide acceptable explanations by analyzing the data. Generally, it is
observed that microbial behavior is inconsistent. Employment of a specific bacteria
type may be successful at times but unsuccessful at other times [23,24]. It is very diffi-
cult to duplicate the prevailing dynamic environment of an underground reservoir in
laboratory [84]. Moreover, in the laboratory studies, the cores’ length is in the range
of inches to a few feet, thus they cannot truly represent the characteristics of the pet-
roliferous formations [736]. The other point is that interaction of the multiplying
microorganisms with the porous media matrix leads to some chemical and physical
changes within the reservoir duplication of which is not possible in the laboratory
[84]. It goes without saying that the studied cores must be acquired from petroliferous
formations. It should be mentioned that many patents on MEOR are based on labo-
ratory studies [736].

10.12.3 Temperature

As it was mentioned before, temperature is the most controlling parameter of the
microbial life in deep biosphere [118]. The most important criteria to apply MEOR
is the reservoir temperature [24]. There is a direct relationship between depth and
temperature, as temperature increases with an increase in depth [25,807]. For example,

the temperature gradient in the North Seas is about 2.5 C/100 m [808]. This indi-

cates a temperature as high as 90 C for depth of 3000 m. Temperatures greater than
80 C are common in oil reservoirs [119]. Bachman et al. [121] mentioned the natural

temperature of oil reservoirs varies from 10 C in the Canadian Athabasca oil sands
[688] to 124 C [8] with the majority in range of 40 80 C [561,809 811]. As the

extreme temperatures, Donaldson et al. [25] mentioned maximum and minimum res-

ervoir temperatures of 404.4 C and 25.6 C in Wyoming and Mississippi, respec-

tively. Temperatures greater than 80 C may prevent anaerobic oil degradation [129].

High temperatures hinder the biochemical production by the microorganisms [25].In
addition, temperature highly influences the enzymes functionality [24]. Enzymes are