The joint research project was started in 2008 to study new microbial enhanced oil recovery (MEOR) method using microbes which convert oil into methane in reservoir. In advance of starting the project， petroleum geochemistry researches were conducted for INPEX domestic oil fields. Clear signs of bio-degradation caused by microbial reactions were observed in some fields while no signs in nearby other fields. Based on the geochemistry research results， we started the project to implement this method in the domestic depleted oil fields. It was intended to initiate the microbial reactions artificially in the reservoir， by injecting water containing microbes. In general， gas recovery factor is higher than that of oil because of the difference in fluid mobility. Therefore， this method can increase hydrocarbon recovery factor by converting immovable oil to movable methane.
In order to evaluate the potential of this method， microbial cultivation experiments have been conducted under the reservoir condition. The bio-augmentation processes were reproduced in the cultivation bottles by mixing oil and water containing the functional microbe communities. The experimental results showed that the oil conversion reactions can be promoted by optimizing cultivation conditions: porous media reproduced by packing sands， in particular. For detailed evaluation under more actual reservoir condition， further microbe cultivation experiment is ongoing in reservoir rock core. In parallel， a field pilot operation is being planned. For estimating the methane producing rate in a well scale， a simple tank model was constructed to evaluate oil conversion reaction near wellbore. Our results show a positive potential of the new MEOR method that converts residual oil into methane in the depleted oil fields.
