HR: 11:35h
AN: OS42A-06    [Abstracts]
TI: Temperature variation in methane hydrate bearing sediments in the eastern Nankai Trough, Japan
AU: * Fujii, T
EM: fujii-tetsuya@jogmec.go.jp
AF: Japan Oil, Gas and Metals National Corporation (JOGMEC), 1-2-2 Hamada, Mihama-ku, Chiba-shi, 261-0025 Japan
AU: Nagakubo, S
EM: nagakubo-sadao@jogmec.go.jp
AF: Japan Oil, Gas and Metals National Corporation (JOGMEC), 1-2-2 Hamada, Mihama-ku, Chiba-shi, 261-0025 Japan
AU: Kawasaki, T
EM: kawasaki-tatsuji@jogmec.go.jp
AF: Japan Oil, Gas and Metals National Corporation (JOGMEC), 1-2-2 Hamada, Mihama-ku, Chiba-shi, 261-0025 Japan
AU: Fukuhara, M
EM: fukuhara@fuchinobe.oilfield.slb.com
AF: Schlumberger K.K., 2-1, Fuchinobe 2-chome, Sagamihara-shi, 229-0006 Japan
AU: Fujii, K
EM: fujii@fuchinobe.oilfield.slb.com
AF: Schlumberger K.K., 2-1, Fuchinobe 2-chome, Sagamihara-shi, 229-0006 Japan
AB: In the Nankai Trough, seismic data indicates widespread existence of BSR, which is interpreted as an indicator of bottom boundary of methane hydrate bearing zone. Methane hydrate is regarded as future possible natural gas resource, although the mechanisms of its occurrence and distribution have been poorly understood. In order to obtain data for the understanding of methane hydrate occurrence and natural reserves estimation, METI exploratory test wells _e_fTokai-oki to Kumano-nada_h were drilled from January to May in 2004 in the eastern Nankai Trough, offshore central Japan. As a part of this project, continuous formation temperature measurement in hydrate bearing sediments in ocean area, the first attempt in the world, was carried out in order to investigate in-situ temperature condition in hydrate bearing sediments and to obtain basic data to evaluate methane hydrate occurrence. Optical fiber sensor was used for the measurement of temperature distribution. Sensor cable was set in the borehole, with the measurement system (data logger) set above the seafloor. 2 kinds of sensor cable, DTS (Distributed Temperature Sensor) and FBG (Fiber Bragg Grating), were set in the borehole. Continuous temperature distribution data for 50 days was obtained successfully at the location where pore space type hydrate was confirmed in sand layer by coring. Averaged temperature depth profile was constructed after analysis such as data conversion, quality control, evaluation of temperature stability, temperature correction and depth correction (Fukuhara et al., 2005). The thermal gradient obtained from temperature depth profile showed good matching with expected thermal gradient in this area (3C/100m), below hydrate bearing zone. On the other hand, apparent lower thermal gradient was observed in hydrate bearing zone and also around lower BSR. In addition, as a result of preliminary estimation of bottom depth of a hydrate stability zone (BGHS) from phase diagram with measured temperature data, significant depth discrepancy between theoretical BGHS and BSR were recognized. The variation of thermal gradient in hydrate bearing zone and below could be related to the exothermic or endothermal reactions accompanied by hydrate formation or dissociation. Further analysis using core, well log and seismic data could bring us useful information to understand this complicate temperature variation. This study was conducted as a part of research consortium for methane hydrate resources in Japan (MH21).
DE: 3004 Gas and hydrate systems
DE: 3015 Heat flow (benthic)
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3022 Marine sediments: processes and transport
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005