Microbial Enhanced Oil Recovery
It is well known from several core scale experiments that microbial activity inside a core
may lead to enhanced oil production. In this work we argue that the only realistic microbial
mechanism that contributes to oil production is that of the biofilm type, simply because of
the low concentration of microbes inside the porous media. Microbial activity can lead to
formation of a biofilm on the rock surface and the oil water interface. By modelling the
microbes as immiscible drops we show that they can change the wetting properties of the
rock. The model used is a Lattice Boltzmann algorithm for solving the multiphase Navier-
Experiments with two strains of microbes from oil fields have been
performed. The experiments are focused on studying the ability of microbes to attach to
interfaces and surfaces and thereby change the wetting properties of oil, brine and rock.
The first type is a microbial capillary tube experiment where microbes grown inside
capillary tubes may change the interfacial or wetting properties of the tubes. A change in
interfacial tension or wetting characteristic can be observed as a change in height of the oil
water interface. The second type is a sessile drop experiment, where the contact angle of an
oil drop has been observed over time, while subjected to microbial activity.
Microbial enhanced oil recovery (MEOR) is motivated by the fact that numerous core
scale experiments have shown an increased oil production due to microbial activity. In
some cases the increased oil production has been extremely high while in some cases very
low (see Bryant and Lockhart (2000)). The experimental evidences are convincing that
something is going on inside the core which increases the oil production. The interpretation
of core scale experiments is complicated due to one simple reason that when oil is released,
one never really knows what kind of mechanism is responsible for the increased oil
production. Even if the microbes or product produced by the microbes was responsible for
the extra oil produced, one does not know precisely what they did. The core acts as a black
box. In order to do a field trial or pilot one needs to understand in detail what the microbes
are doing. As an example core scale experiments are often performed on water wet cores.
If the mechanism for extra oil production is wettability change towards more oil wet
behaviour, then one needs to take into account that the reservoir is probably not water wet,
but mixed wet.
Biofilms can grow on the surface of the porous rock, which may lead to a change of
surface properties and/or a decrease in permeability (Gandler et al. (2006)). Permeability
reduction can not explain increased oil production from water wet cores. The properties of
the biofilm will be different from the rock properties. The change in surface properties
inside the porous rock can thus lead to a change in the wetting properties. If the microbes
locally change the wettability close to a trapped oil cluster, this oil cluster can be mobilized
when the receeding contact angle is reduced sufficiently. In addition microbes attached to
the oil water interface will not detach easily (we will return to this point). Microbes would
then be transported with the oil cluster to a new location and may induce new oil
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