Microbial enhanced oil recovery (MEOR) process utilizes microorganisms or their metabolites to mobilize
the trapped oil in the oil formation after primary and secondary oil recovery stages. MEOR technique is
considered as more environmentally friendly and low cost process. There are several identified mechanisms
for more oil recovery using MEOR processes however; wettability alteration and interfacial tension
(IFT) reduction are the important ones. Enterobacter Cloacae, a facultative bio-surfactant producer bacterium,
was selected as a bacterial formulation due to its known performance on IFT reduction and
wettability alteration. To quantify the effects of these two mechanisms, different tests including oil
spreading, in situ and ex situ core flooding, wettability measurement (Amott), IFT, viscosity and pH
measurements were performed. The obtained results revealed that the experimental procedure used in
this study was able to quantitatively identify the individual effects of both mechanisms on the ultimate
microbial oil recovery. The results demonstrated considerable effects of both mechanisms on the tertiary
oil recovery; however after a proper shut in time period, more tertiary oil was recovered because
of wettability alteration mechanism. Finally, SEM images taken from the treated cores showed biofilm
formation on the rock pore surfaces, which is responsible for rock surface wettability alteration.
