3:00 PM - 3:15 PM
[MIS26-04] High-resolution 3D seismic reflection survey of a shallow off Sakata, eastern margin of the Sea of Japan
Keywords:shallow methane hydrate, high-resolution survey, 3D seismic reflection survey
The existence of natural gas hydrate is known offshore of Japan (Sato et al., 1996). The existence of methane hydrate (MH) deposits in sandy sediment are well known on the Pacific side of Japan. In that type, MH fills the interstices of the particles of subseafloor sand layers. A lot of research works in Japan have been done on this type of HM. On the other hand, on the Sea of Japan side, shallow MH in the mud-dominant sediment near the seafloor, is known.
The National Institute of Advanced Industrial Science and Technology (AIST) has been conducted comprehensive research and development as part of the methane hydrate development promotion project of the Ministry of Economy, Trade and Industry (METI) since 2013. We are currently studying to select the potential locations of MH production test site. One of the candidates is the sea area off Sakata City, Yamagata Prefecture, on the eastern margin of the Sea of Japan. Off Sakata area (tentative name: Sakata Knoll), several research works, such as, acoustic mapping using ships and AUVs, deep-towed control-source electromagnetic exploration (CSEM), logging while drilling (LWD), sampling have been conducted. These results, especially the results of LWD, strongly suggest that shallow MH is present in sediment near the seafloor at the top of the Sakata Knoll.
In this study, we will introduce a high-resolution 3D reflection seismic survey (HR3D) conducted in the area of about 4 km x 10 km (160 survey lines) of Sakata Knoll, for the purpose to investigate the 3D geological structure from the seafloor to several hundred meters below it. The vessel used for data acquisition was "Tsushima" with 188 total tons and hull dimensions of 38m x 8.5m x 3.6m. A GI gun with a chamber size of 150 cubic inches shot every 6.25 m. The streamer cable length used for the HR3D survey was as short as 100 m. Two-dimensional (2D) reflection data were additionally acquired at a survey line interval of 500 m. The velocity information extracted from the 2D data was used for HR3D data processing.
In the data processing, after sorting the data by the common reflection point recording, the bin data that could not be acquired due to such as the bending of the track was estimated by interpolation from the surrounding bin data. In addition, after multiple reflection and ghost reflection suppression, which is characteristic noise sources for the reflection surveys in the marine area, common reflection point stack and post-stack migration were performed.
Since a high-frequency energy source was used in HR3D survey, it became possible to obtain high-resolution results and detect fine geological structures and faults. In particular, by performing 3D migration, a very clear 3D cross section could be obtained. As a result, it was possible to obtain the 3D geological structure from the seafloor (500 m deep) to the depth of about 900 m with high accuracy. In particular, the geological features such as the strike and dip of the high-angle normal faults, which are often found on the northwestern slope of the knoll were clearly imaged.
This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan). Thanks to the cooperation of Yamagata Prefecture, and Yamagata Prefecture Fisheries Cooperative. The seismic reflection data acquisition was carried out with the cooperation of JGI, Inc.
The National Institute of Advanced Industrial Science and Technology (AIST) has been conducted comprehensive research and development as part of the methane hydrate development promotion project of the Ministry of Economy, Trade and Industry (METI) since 2013. We are currently studying to select the potential locations of MH production test site. One of the candidates is the sea area off Sakata City, Yamagata Prefecture, on the eastern margin of the Sea of Japan. Off Sakata area (tentative name: Sakata Knoll), several research works, such as, acoustic mapping using ships and AUVs, deep-towed control-source electromagnetic exploration (CSEM), logging while drilling (LWD), sampling have been conducted. These results, especially the results of LWD, strongly suggest that shallow MH is present in sediment near the seafloor at the top of the Sakata Knoll.
In this study, we will introduce a high-resolution 3D reflection seismic survey (HR3D) conducted in the area of about 4 km x 10 km (160 survey lines) of Sakata Knoll, for the purpose to investigate the 3D geological structure from the seafloor to several hundred meters below it. The vessel used for data acquisition was "Tsushima" with 188 total tons and hull dimensions of 38m x 8.5m x 3.6m. A GI gun with a chamber size of 150 cubic inches shot every 6.25 m. The streamer cable length used for the HR3D survey was as short as 100 m. Two-dimensional (2D) reflection data were additionally acquired at a survey line interval of 500 m. The velocity information extracted from the 2D data was used for HR3D data processing.
In the data processing, after sorting the data by the common reflection point recording, the bin data that could not be acquired due to such as the bending of the track was estimated by interpolation from the surrounding bin data. In addition, after multiple reflection and ghost reflection suppression, which is characteristic noise sources for the reflection surveys in the marine area, common reflection point stack and post-stack migration were performed.
Since a high-frequency energy source was used in HR3D survey, it became possible to obtain high-resolution results and detect fine geological structures and faults. In particular, by performing 3D migration, a very clear 3D cross section could be obtained. As a result, it was possible to obtain the 3D geological structure from the seafloor (500 m deep) to the depth of about 900 m with high accuracy. In particular, the geological features such as the strike and dip of the high-angle normal faults, which are often found on the northwestern slope of the knoll were clearly imaged.
This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan). Thanks to the cooperation of Yamagata Prefecture, and Yamagata Prefecture Fisheries Cooperative. The seismic reflection data acquisition was carried out with the cooperation of JGI, Inc.