Origin and migration-accumulation mechanism of methane gases present in shallow layers of Tokyo Lowland and their disaster risks

Abstract

Origins of methane gases present in shallow layers in the Tokyo Lowland have been investigated. The methane gases have often leaked during construction works such as pile driving, causing fire accidents and sometimes explosions. Based on observations and composition analyses of gas bubbles rising from canal-beds and river-beds, it was clarified that the gases have two kinds of origins: the South Kanto gas field and bottom mud microbials. Since the former is known as the largest gas field in Japan and has a huge amount of gas reserves, the potential risks at the construction works will be never reduced for a long time in the future. From this point of view, a natural gas production and carbon dioxide capture, utilization and storage（CCUS）might be the best solution to reduce the disaster risks from the methane gases in the Tokyo Lowland.