Page 428 - Fundamentals of Enhanced Oil and Gas Recovery

416 Afshin Tatar

10.9.1 Injection of Microbial Bioproducts
If there is no suitable indigenous microorganisms present in the target formation and it
is not possible to inject exogenous microorganisms maybe due to the prevailing harsh
condition, it is possible to directly inject the ex situ produced bioproducts. In this
approach, the metabolic biochemicals are generated outside the well in laboratories and
then the bioproducts maybe along with some synthetic chemicals will be injected. The
advantage of this approach is that the operators are able to exert more direct control on
the process. It is possible to directly select the desired produced compounds to be
injected to the well. The bioproducts will be mixed with water before waterflooding.
To be brief, in this approach, the metabolic bioproducts are injected to well rather than
the microorganisms or nutrients. By this approach, there is a concern about the loss of
injected biochemicals [6]. The other drawback of this approach is the high costs of labo-
ratory equipment, maintenance of the bioreactors, facilities, and purification practices
compared with lower yield of the induced production [24,31]. Because of this, direct
injection of bioproducts may not be economically feasible.

10.9.2 Stimulation of Indigenous Microorganisms
In this approach, the microorganisms indigenous to the reservoir will be stimulated to
generate the desired bioproducts. For this, it is necessary the microorganisms doing
the preferred function (bioplugging or producing biochemicals) are present. If the
proper microorganisms are already present, the next step is deciding how to stimulate
them. Analysis of the produced fluids as well as core sample (if available) can be help-
ful in making the decision [6]. A standardized framework such as specialized sampling
in coring techniques is essential for evaluation of microbial activity [415]. There are
some procedures that minimize the contamination problems during the core material
sampling [416]. Youssef et al. [6] mentioned both molecular and microbial techniques
to confirm the presence of the suitable microorganisms. After this, the next step is to
apply more tests to verify the production of desired biochemicals or activity [6].
Despite the exogenous microorganisms, which may be unable to adapt with the reser-
voir condition, the indigenous ones have more chance to thrive under the reservoir
condition [23]. In economic point of view, the indigenous bacteria are more desired
as it is only necessary to supply the nutrients. It is important to find a way to selec-
tively stimulate only the target microorganisms. In order to stimulate the aerobic
microorganisms, it is necessary to inject oxygen or chemical, which can be converted
to oxygen (such as hydrogen peroxide (H 2 O 2 )) [6].

10.9.3 Injection and Stimulation of Exogenous Microorganisms
In cases in which the desired microorganisms are not present, an alternative is inject-
ing and stimulating exogenous microorganisms. In this approach, the microorganisms