Successful application of microbial enhanced oil recovery requires a lot of understanding of not only the
reservoir properties but also an understanding of the
effect of microbial treatment on reservoir rocks in order
to get a desirable result.
The experiment with treatment
of carbonate rocks with a media inoculated with a strain
of Clostridium tryobutryrium indicated porosity increase
in the course of the experiment. The porosity increase
observed in all the rock samples was mainly due to significant dissolution of carbonate by the organic acids
produced during microbial metabolism. The pattern of
dissolution lead to reduction in the bulk volume with
pore volume slightly reduced or generally remains in
the pore spaces. The effect on pH is clearly related to the
concentration of Ca2+ ions in the media over time due
to bacteria metabolism or those coming from salinity
alone, however the electrical conductivity shows a weak
correlation with calcium ions release suggesting that
the calcium ions in this media are not completely dissociated. Since modification of rock properties during
microbial process can be positively applicable in increasing the reservoir porosity can expose larger fraction
of the reservoir rock and inducing wettability that can
improve oil recovery due to the type of nutrient chalk
with C. tryobutyrium.