Verification of microbial activities for microbial restoration of methane deposit with subsurface CO₂ sequestration into the depleted oil fields

The objective of this research is to estimate the possibility of microbial restoration of methane deposits using subsurface sequestered CO₂ and indigenous anaerobes in depleted oil fields. The most important factors are the efficiency and velocity of methane conversion by indigenous anaerobes inhabiting a reservoir. Field samples (producing oil and water) from oil field in Japan were collected and analyzed in order to clarify the existence and survivability of indigenous methane-producing anaerobes under reservoir conditions. The hydrogenotrophic methanogen consortium MYH-4 consortium was separated from the enrichment culture added oil reservoir water. By using MYH-4 consortium, two experiments were conducted. (i)Direct calculation of the CO₂ to methane conversion rate for economic assessment. (ii)As the main objective of the field operation test, it is necessary to identify the state of the subsurface injection environment and the limitations that it poses to methane production. To clarify this, the experiment was carried out by using stable isotope probing. At the result of these studies, it has been understood that the methane conversion efficiency from CO₂ was approximately 50%.