5:15 PM - 6:45 PM
[MIS22-P04] Wireline logging results for researching physical property of methane hydrate reservoirs of off Joetsu and off Sakata area in the Japan Sea
Keywords:surface gas-hydrate, wireline logging, physical property, Sonic velocity
The research of the deep marine surface-methane hydrate (SMH) in the National Institute of Advanced Industrial Science and Technology (AIST) was started as the resource survey to grasp the amount of their volume since 2013 to 2015, then, until 2018, the feasibility study of how to develop it had been studied. Since 2019, R&D have been progressed as the trinity of the production method development, resource survey for production test, and evaluation of environment effect. Especially in this phase, we have started the geomechanical study of SMH sediments at 2 area of methane hydrate reservoir. One of them was the research campaign at the off-Joetsu area and the off-Sakata area using D/V Chikyu struggled in September, 2022 and August, 2023. Both champaign was successfully done finally, and many sediment core samples and wireline logging results, such as sonic, nuclear-magnetic resonance , resistivity, density and sigma, were gathered. Moreover, geomechanical tests in on-vessel and on-shore laboratory had been done on sediment cores those were retrieved.
We have drilled the set of methane hydrate site and reference site, at the Sakata knoll, Joetsu knoll and Umitaka spur during the campaigns. At first, we tried to grasp the physical properties of sediments at SMH site by cone-penetration test, directly, but it was hardly to penetrate SMH. Also, variation of methane hydrate morphology made sediments' property widely, so that it is quite difficult to unveil their heterogeneity. Thus, we grasped the sediment properties from the results of the reference site without SMH by wireline logging, then interpret the SMH sediments at the MH site. Analysis of Sakata-knoll MH site using the resistivity, density and P/S wave-velocity relationships, highly concentration of SMH is only distributed until the depth of 20mBSF, which is quite shallower than the depth of the base of gas hydrate stability zone (BGHSZ) that estimated from geothermal gradient. On the contrary, gas hydrate is observed the depth until nearly BGHSZ at Joetsu knoll and Umitaka spur, those depth were 106mBSF and 96mBSF, respectively. The gas hydrate saturation varied from 0 to 100% in depth, which is only corresponded with resistivity, partially. It implies that relationships between hydrate saturation and resistivity would not be unique, and could be changed by various morphology of MH, salinity, and existence of gases. We will discuss the structures and properties of SMH within hydrate reservoir not only resistivity but also considering from the neutron capture cross-section for chloride, sonic velocity for properties and geomechanical test results in presentation.
This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan).
We have drilled the set of methane hydrate site and reference site, at the Sakata knoll, Joetsu knoll and Umitaka spur during the campaigns. At first, we tried to grasp the physical properties of sediments at SMH site by cone-penetration test, directly, but it was hardly to penetrate SMH. Also, variation of methane hydrate morphology made sediments' property widely, so that it is quite difficult to unveil their heterogeneity. Thus, we grasped the sediment properties from the results of the reference site without SMH by wireline logging, then interpret the SMH sediments at the MH site. Analysis of Sakata-knoll MH site using the resistivity, density and P/S wave-velocity relationships, highly concentration of SMH is only distributed until the depth of 20mBSF, which is quite shallower than the depth of the base of gas hydrate stability zone (BGHSZ) that estimated from geothermal gradient. On the contrary, gas hydrate is observed the depth until nearly BGHSZ at Joetsu knoll and Umitaka spur, those depth were 106mBSF and 96mBSF, respectively. The gas hydrate saturation varied from 0 to 100% in depth, which is only corresponded with resistivity, partially. It implies that relationships between hydrate saturation and resistivity would not be unique, and could be changed by various morphology of MH, salinity, and existence of gases. We will discuss the structures and properties of SMH within hydrate reservoir not only resistivity but also considering from the neutron capture cross-section for chloride, sonic velocity for properties and geomechanical test results in presentation.
This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan).