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Geological information is essential for a country like Japan, located at a tectonically active area, to ensure a safe and secure society. The Geological Survey of Japan gathers, compiles, and provides geological information and promotes its wider use. We also develop technologies to overcome various difficulties related to global environment protection, exploration of minerals and energy resources, and natural disaster mitigation, and coordinate international cooperation as a national representative.
Researchers from AIST, in collaboration with Massachusetts Institute of Technology, have discovered that methanogenic archaea ("methanogens") living underground can change the "indicators" of thermogenic natural gas to those of biogenic gas. This could significantly change the information on the origins and reserves of natural gas, raising the possibility of uncovering new natural gas deposits that have previously been overlooked. Understanding where and how methane, the main component of natural gas, is produced is crucial for assessing global natural gas resources. Until now, "stable isotope signals" have been used as an indicator to distinguish the origin of methane. However, this approach has faced a major problem that has remained unsolved for nearly half a century: the stable isotope signal of biogenic methane produced by methanogens in the subsurface cannot be reproduced in a laboratory methanogen culture. In this study, researchers developed a high-pressure culture system that can faithfully simulate the underground conditions. Using this system, they achieved a world-first: experimentally replicating the stable isotope signals of biogenic methane produced underground. Furthermore, they uncovered a surprising phenomenon: methanogens can alter the stable isotope signals of coexisting thermogenic methane, effectively overwriting them to mimic those of biogenic methane. This discovery indicates that the quantity of thermogenic methane may have been underestimated, and highlights the need for a significant revision of our understanding about the origins of the natural gas deposits. Consequently, these findings prompt a reevaluation of exploration methods for natural gas deposits, raising the possibility of discovering previously overlooked reserves.
The origins of methane in natural gas deposits and the phenomenon of methanogens overwriting the origin indicators
In 2020, AIST researchers estimated the microbially mediated methane consumption rate by chemical and microbiological analyses coupled with stable isotope tracer experiments of sediments collected from the seafloor off Sakata City, Yamagata Prefecture, where methane hydrates are distributed. They also discovered that in the redox transition zone below the seafloor, methane-oxidizing microorganisms that require oxygen for growth (aerobic methanotrophs) and those that do not (anaerobic methanotrophs) are metabolically active and consume methane. These findings contribute to an accurate understanding of the seafloor budget of methane.
Methane consumption rate was estimated by geochemical and microbiological analyses and incubation experiments of subseafloor sediments. *Figure modified from Miyajima et al. (2024)
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