Microbial enhanced oil recovery (MEOR) is receiving renewed interest worldwide in recent years as a viable method while not damaging the reservoir is proven to be remarkably effective, however to some extent costly. This method is based on microorganisms' activities to reduce residual oil of reservoirs, which is dependent on behavior of inherent microorganisms or injection of bio-product of external microorganisms.
In this work, five bacterial species were taken from MIS crude oil that is one of the aging Persian fractured reservoirs. These microorganisms are substantially strong in increasing oil recovery especially by reducing IFT and other MEOR mechanisms such as change of wettability of rock at the favorable condition for the activities of these bacteria observed within the temperature range of 50°C to 90°C at the atmospheric pressure.
Two series of visualization experiments were carried out to examine the behavior of microbial enhanced oil recovery in micromodels designed to resemble the fractured system: static and dynamic. In the static one, carbonate rock-glass micromodel is used to simulate the reservoir conditions and the latter is performed by a glass micromodel which has a fracture with 45 degree inclination. The image processing methodology is used to determine the recovery achieved by MEOR in the micromodel made of glass.
A prevalent question in the oil industry is: what is the best method for improving the recovery factor of a certain reservoir? Jumping to the answer is not always an easy task. The effectiveness of a method in a specific reservoir does not necessarily guarantee the chance of success somewhere else.
Essentially the prevailing condition of a reservoir is the determining factor in success or failure of a method. So, if the method is designed in a way the least affecting the reservoir, there would be a higher chance of success. MEOR is one of these lately high-profile methods. Even though, this method can be very powerful, but its associating problems are still to be taken into thorough consideration.
MEOR has long been considered by hydrocarbon-related scientists and microbiologists as an effective method to recover tertiary oil from reservoirs. MEOR can recover tertiary oil by improving macroscopic sweep efficiency through microbially induced permeability profile modification; or reducing interfacial tension between oil and water with microbial bio-surfactants to lower the capillary trapping forces; or stimulating the reservoir porosity and permeability with microbial products such as acids, or combining all three mechanisms. This paper concentrates mainly on the application of bio-organisms which are also referred to as microorganisms throughout this study to recover residual oil trapped within the pores of a rock. The glass micromodels are largely used for visualization purposes in literature. In addition to conventional micromodels two other types were also utilized which could be considered as hybrid models of the reservoir rock and a micromodel.
At the end of the water-flooding of reservoirs, a large quantity of oil may remain trapped within the reservoir. The oil is retained by capillary forces acting on oil globules within the porous medium. Surfactants reduce capillary forces by lowering the interfacial tension between oil and water. This allows any displacing force such as the viscous force of injected or flowing surfactant to recover some of this oil. Microbial bio-surfactants are similar to synthetic surfactants in terms of the oil recovery mechanism. What differentiates them from synthetic surfactants is that they are generated in situ, inside the reservoir, by microbes when sufficient nutrients and suitable conditions are present.
A new surface sample of the MIS oil was taken at the well head and physical specifications were measured at the lab. This is fairly light oil with API gravity of 42.5. The respective specifications are according to the table 1.