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[MIS20-08] Controlling Factors on the Biogenic Gas Generation along the Sea of Japan : A Case Study of Niigata Area
Keywords:Biogenic Gas, Niigata, Methane Hydrate
Biogenic Gas has been attracting attention as a new exploration target in offshore Japan. Identifying key factors controlling biogenic gas generation is essential for exploration and exploitation. Suzuki et al. (2024) proposed the comprehensive concept in the Nankai Trough subduction area. On the other hand, along the Sea of Japan within the back arc setting, no comprehensive concept has been proposed so far, especially from the perspective of exploration.
Niigata is one of the best areas to represent the general exploration concepts of biogenic gas as this area is one of the most prolific regions along the Sea of Japan.
The presence of biogenic gas and common factors of biogenic gas formation were compiled from MITI/METI(Ministry of Investment, Trade and Industry/Ministry of Economy, Trade and Industry, Japan)exploratory wells onshore and offshore Niigata. In addition, we have also interpreted supply pathways of fluids from deeper strata using seismic reflection data.
As a result of the preliminary examination, the following common findings were identified in Niigata area. Mud gas analysis confirmed the mixing of biogenic and thermogenic gas in most wells. In addition, a higher geothermal gradient compared to the Pacific side and a faster sedimentation rate cause a narrow biogenic gas generation zone. These suggest mature source rocks lie deeper than the biogenic gas generation zone in Niigata area. Hydrocarbons generated in these deep formations likely to migrate upward, where microbial decomposition forms biogenic gas. 3D seismic data suggest the presence of deep-reaching faults near BSRs (Bottom simulating reflectors) and mud volcanoes, which are interpreted to act as fluid pathways from deeper to shallower formations.
We concluded that hydrocarbons expelled from the deeply buried source rocks in Niigata area are likely to act as the fluids required for biogenic gas generation by migrating to shallower formations through deep-reaching faults.
We are expanding the area of interest to other basins along the Sea of Japan, while exploring the applicability of quantitative evaluation criteria that reflect regional differences.
Acknowledgement
This study was conducted as part of the National Program for Oil and Natural Gas Prospecting (Kokunai Kisochosa) led by the Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry (METI). We would like to express our gratitude to the agency for permission to use the survey data.
References
Suzuki et al. (2024) Communications Earth & Environment. 5, 97.
Niigata is one of the best areas to represent the general exploration concepts of biogenic gas as this area is one of the most prolific regions along the Sea of Japan.
The presence of biogenic gas and common factors of biogenic gas formation were compiled from MITI/METI(Ministry of Investment, Trade and Industry/Ministry of Economy, Trade and Industry, Japan)exploratory wells onshore and offshore Niigata. In addition, we have also interpreted supply pathways of fluids from deeper strata using seismic reflection data.
As a result of the preliminary examination, the following common findings were identified in Niigata area. Mud gas analysis confirmed the mixing of biogenic and thermogenic gas in most wells. In addition, a higher geothermal gradient compared to the Pacific side and a faster sedimentation rate cause a narrow biogenic gas generation zone. These suggest mature source rocks lie deeper than the biogenic gas generation zone in Niigata area. Hydrocarbons generated in these deep formations likely to migrate upward, where microbial decomposition forms biogenic gas. 3D seismic data suggest the presence of deep-reaching faults near BSRs (Bottom simulating reflectors) and mud volcanoes, which are interpreted to act as fluid pathways from deeper to shallower formations.
We concluded that hydrocarbons expelled from the deeply buried source rocks in Niigata area are likely to act as the fluids required for biogenic gas generation by migrating to shallower formations through deep-reaching faults.
We are expanding the area of interest to other basins along the Sea of Japan, while exploring the applicability of quantitative evaluation criteria that reflect regional differences.
Acknowledgement
This study was conducted as part of the National Program for Oil and Natural Gas Prospecting (Kokunai Kisochosa) led by the Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry (METI). We would like to express our gratitude to the agency for permission to use the survey data.
References
Suzuki et al. (2024) Communications Earth & Environment. 5, 97.