Preliminary Risk Assessment of Microbial Associated CO₂ Geological Storage and CH₄ Production (Bio-CCS)

Abstract

Among in-situ microbes within depleted oil-gas reservoir, the species dominant in CO₂ rich environment produce methane much faster than those dominant in CO₂ poor environment. CO₂ acts as a catalyst in the reaction. If we maintain preferable conditions for methanogenic microbes during geological CCS, we will be able to abate greenhouse gas emission and produce natural gas as one of natural energy resources at the same time. We named the technological concept as‘ Microbial Associated Geological CCS (Bio-CCS)'. In Bio-CCS, CO₂ will be injected from a well for two purposes: to abate greenhouse gas emission and to cultivate methanogenic geomicrobes. CH₄ gas will be produced later using other wells. The procedure is similar to the Enhanced Oil/Gas Recovery (EOR/EGR) operation, but in Bio-CCS, the target is production of methane gas out of residual oil in depleted oil/gas reservoir CO₂ abatement. To evaluate the basic feasibility of the new conceptual technology, we conducted preliminary risk assessment of Bio-CCS conceptual process. First of all, based on result of numerical calculations using geological model of Bio-CCS process, we assumed a procedure of Bio-CCS site: 1 million CO₂ will be injected into depleted oil reservoir in 10 years; the reservoir will be kept still for 90 years and 0.5 million t CH₄ will be produced; after 100 years from the first CO₂ injection, CH₄ production will be started. We developed hazard scenarios by way of literature survey and statistical analysis of accident statistics. Then we applied the hazard scenarios to the assumed Bio-CCS procedure. As the result, the preliminary risk assessment assures that the Bio-CCS process will be safe. Even it happens any leaking accidents, most impacts on peripheral area of Bio-CCS site will be negligible.