9:30 AM - 9:45 AM
[MIS22-03] Drilling survey on the shallow methane hydrate-bearing area off Sakata and Joetsu, Sea of Japan.
Keywords:shallow methane hydrate, off Sakata, off Joetsu, Drilling survey, Geotechnical survey, The D/V Chikyu
Since 2013, marine geological and environmental survey for shallow methane gas hydrate production are conducting by the National Institute of Advanced Industrial Science and Technology (AIST) funded by METI (the Ministry of Economy, Trade and Industry, Japan). Geomechanical information of the hydrate-bearing sediments are important, because direct drilling method is proposed for natural gas recovery and production from shallow methane gas hydrate, which are occurred in shallow unconsolidated sediments bellow seafloor. Therefore we conducted three cruises for geomechanical survey on hydrate-bearing areas, off Sakata area in August 2021 (PS21 Research Cruise), off Joetsu area in September 2022 (CK22-03C Research Cruise) and both area in August 2023 (CK23-02C Research Cruise). In this presentation, we report the general information of those three Research Cruises during 3 years.
PS21 Research Cruise were conducted used by the D/V Poseidon-1 belonging to the Fukada Salvage & Marine works Co., Ltd, and CK22-03C and CK23-02C Research Cruises were conducted used by the D/V Chikyu belonging to the JAMSTEC.
We drilled every 2 sites on 3 areas. One site is on mound bellow which methane hydrate occurred (MH site), another site is on no-hydrate site (RE site), all of 3 areas. Drilling depth were 160 mbsf at SK-MH site (WD 532.5 m) and SK-RE site (WD 556.0 m) , 200 mbsf at JK-MH site (WD 981 m), 144 mbsf at JK-RE site (WD 984 m), 122 mbsf at UTN-MH site (WD 916 m) and 144 mbsf at UTN-RE site (WD 925 m), and all of those depth were deeper than estimated depth of base of gas hydrate stability (BGHS). We finally fixed the drilling position according to the seafloor observation by ROV, thus we were able to keep adequate distances and directions from previous holes.
Sediment core sampling and wireline logging were successfully conducted on all of those holes. Continuous sediment cores bellow seafloor were recovered of 41m length at SK-RE site, 99m at JK-RE site and 90m at UTN-RE site, but limited recovery at other depth because of hard sediment, such as solid gas hydrate and carbonate rocks, and limited ship times. Total recovered length of cores were 30m at SK-MH site, 32 m at JK-MH site and 12 m at UTN-MH site.
On D/V Chikyu, recovered sediment cores were immediately sampled for gas and interstitial water analysis, after that, nondestructive measurement such as X-ray CT scan and multi sensor core truck (MSCL) were conducted. After measurement, cores were sorted to whole-round core for onshore geomechanical soil test and split core for onboard description, sub-sampling and measurements, based on XCT-images. On D/V Poseidon-1, only gas and interstitial water sampling were conducted onboard, all of rest processes were conducted onshore after cruise.
Wireline logging were conducted at all 6 sites, at where continuous data, such as velocity, resistivity, natural gamma ray, NMR, density, etc. from seafloor to 110 or 170 mbsf were acquired, however some data are lacked because of problem of logging tools and limited ship times.
Onboard geomechanical measurement data, onshore geomechanical soil test data, wireline logging data and CPT measurement data (PS21 only) are analyzed for geomechanical property evaluation of hydrate-bearing or around hydrate sediments. Geochemical and sedimentological analysis, and dating data (from tephra, microfossil, carbon isotope, etc.) will be use as geological background data for geomechanical property evaluation.
This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan).
PS21 Research Cruise were conducted used by the D/V Poseidon-1 belonging to the Fukada Salvage & Marine works Co., Ltd, and CK22-03C and CK23-02C Research Cruises were conducted used by the D/V Chikyu belonging to the JAMSTEC.
We drilled every 2 sites on 3 areas. One site is on mound bellow which methane hydrate occurred (MH site), another site is on no-hydrate site (RE site), all of 3 areas. Drilling depth were 160 mbsf at SK-MH site (WD 532.5 m) and SK-RE site (WD 556.0 m) , 200 mbsf at JK-MH site (WD 981 m), 144 mbsf at JK-RE site (WD 984 m), 122 mbsf at UTN-MH site (WD 916 m) and 144 mbsf at UTN-RE site (WD 925 m), and all of those depth were deeper than estimated depth of base of gas hydrate stability (BGHS). We finally fixed the drilling position according to the seafloor observation by ROV, thus we were able to keep adequate distances and directions from previous holes.
Sediment core sampling and wireline logging were successfully conducted on all of those holes. Continuous sediment cores bellow seafloor were recovered of 41m length at SK-RE site, 99m at JK-RE site and 90m at UTN-RE site, but limited recovery at other depth because of hard sediment, such as solid gas hydrate and carbonate rocks, and limited ship times. Total recovered length of cores were 30m at SK-MH site, 32 m at JK-MH site and 12 m at UTN-MH site.
On D/V Chikyu, recovered sediment cores were immediately sampled for gas and interstitial water analysis, after that, nondestructive measurement such as X-ray CT scan and multi sensor core truck (MSCL) were conducted. After measurement, cores were sorted to whole-round core for onshore geomechanical soil test and split core for onboard description, sub-sampling and measurements, based on XCT-images. On D/V Poseidon-1, only gas and interstitial water sampling were conducted onboard, all of rest processes were conducted onshore after cruise.
Wireline logging were conducted at all 6 sites, at where continuous data, such as velocity, resistivity, natural gamma ray, NMR, density, etc. from seafloor to 110 or 170 mbsf were acquired, however some data are lacked because of problem of logging tools and limited ship times.
Onboard geomechanical measurement data, onshore geomechanical soil test data, wireline logging data and CPT measurement data (PS21 only) are analyzed for geomechanical property evaluation of hydrate-bearing or around hydrate sediments. Geochemical and sedimentological analysis, and dating data (from tephra, microfossil, carbon isotope, etc.) will be use as geological background data for geomechanical property evaluation.
This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan).