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Abstract
Fujii, T., M. Nakamizu, Y. Tsuji, T. Namikawa, T. Okui, M. Kawasaki, K. Ochiai, M. Nishimura, and O. Takano,
DOI:10.1306/13201112M893350
2009 by The American Association of Petroleum Geologists.
Methane-hydrate Occurrence and Saturation Confirmed from Core Samples, Eastern Nankai Trough, Japan
Tetsuya Fujii,1 Masaru Nakamizu,2 Yoshihiro Tsuji,3 Takatoshi Namikawa,4 Toshiharu Okui,5 Masayuki Kawasaki,6 Koji Ochiai,7 Mizue Nishimura,8 Osamu Takano9
1Technology and Research Center, Japan Oil, Gas and Metals National Corporation (JOGMEC), Japan
2Technology and Research Center, Japan Oil, Gas and Metals National Corporation (JOGMEC), Japan
3Technology and Research Center, Japan Oil, Gas and Metals National Corporation (JOGMEC), Japan
4Japan Petroleum Exploration Co., Ltd., Tokyo, Japan
5Gas Resources Department, Tokyo Gas Co., Ltd., Japan
6Japan Drilling Co., Ltd. (JDC), Japan
7INPEX Corporation, Japan
8Research Center, Japan Petroleum Exploration Co., Ltd., Japan
9Research Center, Japan Petroleum Exploration Co., Ltd., Japan
ACKNOWLEDGMENTS
Drilling of the METI Tokai-oki to Kumano-nada wells was planned and financed by METI. The methane hydrate research program has been conducted by the MH21 research consortium consisting of JOGMEC, National Institute of Advanced Industrial Science and Technology, and Engineering Advancement Association of Japan, with financial support from METI. The domestic survey team of JOGMEC managed the well
drilling exercise. We would like to thank METI and JOGMEC for providing permission to publish this report. Full bore Formation Micro Imager and LithoQuickLook are trademarks of Schlumberger.
ABSTRACT
The Ministry of Economy, Trade and Industry, Japan, drilled the Tokai-oki to Kumano-nada exploratory test wells to obtain data for understanding the occurrence of methane hydrate and estimating the volume of gas stored as methane hydrates in the Nankai Trough, offshore central Japan. In this project, we conducted logging while drilling at 16 sites, coring at four sites, wireline logging at two sites, and long-term monitoring of formation temperature at a single site.
Massive or layered methane hydrates within muddy layers were recovered at sites 1 and 2 by drilling with a conventional wireline-core system. The methane-hydrate-bearing sediments in these sites are a combination of clay and silt, which is not commonly considered a favorable host sediment for hydrate formation; however, a significant decrease in core temperature was recorded within intervals of layered hydrates.
Pore-space-type hydrates were identified in sand layers from sites 4 and 13 within 82 m (269 ft) of recovered core using a pressure temperature core sampler (PTCS). Sediments within this core are mainly very fine- to fine-grained turbidite sand layers of several centimeters (inches) to 1.5 m (5 ft) in thickness (average of 20–40 cm [8–16 in.]). Core-temperature measurements and the relationship between well
-
log
resistivity and grain-size distribution indicate that methane hydrate is concentrated within layers of coarse-grained sand. We identify five sedimentary facies on the basis of a lithological column created from core and
well
-
log
data at sites 4 and 13. Facies
analysis
indicates that the depositional environment in hydrate-bearing zones at sites 4 and 13 consisted of distributary channels to distal lobes within a submarine-fan system. Shipboard hydrate dissociation tests on PTCS cores reveal that average hydrate saturation in the cored sand layers ranged from 55 to 68%, with the average sediment porosities ranging from 39 to 41%, based on the
analysis
of both
well
-
log
and core measurements.
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