Microbial enhanced oil recovery (MEOR) is well-known as a developing and promising method to improve the oil recovery through microbial's activities. The basic theory behind this is very simple. Specifically selected suitable nutrients are introduced into the producing formation near the wellbore. When the well is shut-in, after nutrients injection, the microbes are encouraged to produce biometabolites and extend colonization outward into the producing formation. Bioproduction of solvent, polymer, and surfactant is done in-situ. when the well is put into production, the fluids flow toward the wellbore, and result in increasing oil recovery.

MEOR had been applied in some old oil fields in Indonesia, such as Prabumulih field (1992), Klamono and Kawengan fields (1993). By that time, a research group was set up to conduct an intensive research on MEOR in LEMIGAS. Samples were collected from Indonesian oil fields, i.e. Rantau, Jambi, Prabumulih, Cirebon, and Cepu fields. Several potential microbes were identified. However, for the first priority microbes from Cepu fields only were further tested in coreflooding. Beside that, variety of medium were formulated to promote bi-osurfactant, biosolvents, and bioacid production.

To simulate the MEOR processes, coreflood experiments were conducted using standard and native cores, and activated microbes from Cepu oil field at reservoir conditions. The mixed cultures were injected into core sample, after completing a waterflood. The core was shut in to let microbes to produce bi-ometabolites. Nutrient or brine was then injected as a post flood. The injection results indicated that the oil recovery increased 10% to 60% of Sor. SEM and X-ray analyses results revealed no damage on the core samples. The permeability test, after the injection of microbes, showed an insignificant decrease on the standard cores. The decrease was significant, however, for the native cores.

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