Fusion of 3D seismic exploration and seafloor geochemical survey for methane hydrate exploration*

Sadao Nagakubo; Toshiaki Kobayashi; Tetsuya Fujii; Takao Inamori

doi:10.1071/EG07005

RESEARCH ARTICLE

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Fusion of 3D seismic exploration and seafloor geochemical survey for methane hydrate exploration^*

Sadao Nagakubo ¹ ² Toshiaki Kobayashi ¹ Tetsuya Fujii ¹ Takao Inamori ¹

+ Author Affiliations

- Author Affiliations

¹ Japan Oil, Gas and Metals National Corporation, 1-2-2, Hamada, Mihama-ku, Chiba city, Chiba 261-0025, Japan.

² Corresponding author. Email: nagakubo-sadao@jogmec.go.jp

Exploration Geophysics 38(1) 37-43 https://doi.org/10.1071/EG07005
Submitted: 29 November 2006 Accepted: 18 December 2006 Published: 5 April 2007

Abstract

The MH21 Research Consortium has conducted a high-resolution 3D seismic survey and a seafloor geochemical survey, to explore methane hydrate reservoirs in the eastern Nankai Trough, offshore Japan. Excellent geological information about shallow formations was obtained from the high-resolution 3D seismic survey, which was designed to image the shallow formations where methane hydrates exist. The information is useful in constructing a geological and geochemical model, and especially to understand the complex geology of seafloor, including geochemical manifestations and the structure of migration conduits for methane gas or methane-bearing fluid.

By comparing methane seep sites observed by submersibles with seismic sections, some significant relationships between methane hydrate reservoirs, free gas accumulations below the seafloor, and seafloor manifestations are recognised. Bathymetric charts and seafloor reflection amplitude maps, constructed from seismic reflections from the seafloor, are also useful in understanding the relationships over a vast area. A new geochemical seafloor survey targeted by these maps is required.

The relationships between methane hydrate reservoirs and seafloor manifestations are becoming clearer from interpretation of high-resolution 3D seismic data. The MH21 Research Consortium will continue to conduct seafloor geochemical surveys based on the geological and geochemical model constructed from high-resolution 3D seismic data analysis.

In this paper, we introduce a basis for exploration of methane hydrate reservoirs in Japan by fusion of 3D seismic exploration and seafloor geochemical surveys.

Key words: BSR, seafloor geochemical survey, high-resolution 3D seismic survey, methane hydrate, Nankai Trough.

Acknowledgments

The authors express special thanks to J. Ashi (University of Tokyo), U. Tsunogai (University of Hokkaido), M. Tanahashi (National Institute of Advanced Industrial Science and Technology), and R. Sassen (Texas A&M University) for valuable advice and suggestions throughout this study. We also express thanks to M. Nakamizu and T. Saeki (Japan Oil, Gas and Metals National Corporation) who have encouraged us to write this paper and to the Ministry of Economics, Trade and Industry (METI), the Research Consortium for Methane Hydrate Resources and the Japan Oil, Gas and Metals National Corporation which gave permission to publish this paper.

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^* Part of this paper was presented at the 8th SEGJ International Symposium, 2006.