This paper demonstrates a comprehensive preparation study of field injection microbial nutrient starting from a quite extensive screening to select a field and wells, followed by a series of laboratory experiment seeking an optimum nutrient for the in-situ microbes through some oil properties examinations after giving the treatment. The laboratory examines many combination of nutrient to formulate an optimum nutrient, and compares oil sample compositions before and after treating at the optimum nutrient. The general screening evaluates field candidates based on the remaining oil in place, average porosity and average permeability for many fields in Indonesia. Having the field candidate is then followed by an Enhanced Oil Recovery screening that is a combination of Aladasani and Bryant methods. Hence, Bentayan Field is chosen and two wells were selected BN-38 and BN-81. We are confident that this field is possibly unfavorable for most EOR methods other than the MEOR. The laboratory experiment observed total bacteria number during the incubation period that was conducted every 7 days with method of Total Plate Count (TPC) on Nutrient Agar (NA) medium for aerobe facultative bacteria and Reinforced Clostridial Medium (RCM) for anaerobe bacteria. The results can be summarized and concluded that the optimum nutrient composition consists of molasses, nitrogen salts of (NH4)2PO4, and phosphate salt of NPK for BN-38 well is different from the one for BN-81 well, especially, the concentration of molasses. The oil composition after the treatment observed by GC/MS, clearly indicates becoming a much lighter composition then the previous to the extent that the heptane plus is degraded up to more than 30%. This irreversible mechanisms consequence to the viscosity reduction of up to 43.68% and 47.83% for BN-38 and BN-81, respectively. In addition, the imbibition experiment using synthetic core samples yield results of ultimate recovery factor of 56% at an optimum soaking time of 7 days for BN-81. Finally, a schematic diagram of field implementation the injection is presented that is much simpler than the microbial injection since does not need a cultivation tank at the surface.

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