Controle estrutural-estratigráfico na distribuição de hidratos e gases livres do anticlinal Umitaka, Bacia Joetsu, margem leste do Mar do Japão
Palavras-chave:
Bacia Joetsu, chaminés de gás, exsudações de metano, hidratos de gás, Mar do Japão, sísmica monocanal, Umitaka SpurResumo
A Universidade de Tóquio, associada a outras instituições de pesquisas japonesas, tem implementado desde 2004 uma intensa atividade exploratória na Bacia Joetsu, margem leste do Mar do Japão, com a intenção de delimitar acumulações de hidratos de gás. Estes estudos têm integrado dados geofísicos, geológicos e geoquímicos, tendo identificado acumulações rasas de hidratos de gás, associadas a exsudações ativas de metano no fundo do mar e na coluna d’água. A principal ocorrência destas acumulações está localizada em um anticlinal assimétrico denominado Esporão Umitaka (Umitaka Spur), onde levantamentos sísmicos 2D monocanais têm revelado estruturas em forma de chaminés, as quais parecem estar fortemente controladas por um complexo sistema de falhas de plano axial. Estas chaminés apresentam branqueamento de refletores, característica da presença de gás, ocasionalmente exibindo fortes amplitudes sísmicas em seu interior. Algumas vezes podem se observar estruturas pull-up, provavelmente relacionadas a densas acumu-ações de hidratos de gás, cuja impedância acústica é mais elevada. Um refletor que simula o fundo marinho (bottom-simulating reflector - BSR) é visível dentro das chaminés de gás e no flanco leste mais suave do anticlinal assimétrico, sugerindo que os hidratos podem estar selando acumulações rasas não convencionais de gás livre abaixo da zona de estabilidade de hidratos (gas hydrate stability zone - GHSZ). Neste flanco ocorrem depósitos de fluxo de detritos (debris-flow deposits) que podem, a depender de condições permoporosas favoráveis, representar potenciais reservatórios para hidratos dentro da GHSZ e para gases livres abaixo desta. O sistema de falhas axiais, a geometria do anticlinal e as camadas e contatos carreadores induzem a migração de gás termogênico para o topo da estrutura, alimentando a GHSZ e formando intensas exsudações e plumas gigantes de metano na coluna d’água.
Referências
AOYAMA, C.; MATSUMOTO, R. Acoustic surveys of methane plumes by quantitative echo sounder in Japan Sea and estimate of the seeping amount of the methane hydrate bubbles. Journal of Geography, Indiana, v. 118, n. 1, p. 156-174, 2009.
BERNDT, C.; BÜNZ, S.; CLAYTON, T.; MIENERT, J.; SAUNDERS, M. Seismic character of bottom simulating reflectors: examples from the mid-Norwegian margin. Marine and Petroleum Geology, Guildford, v.21, n. 6, p. 723-733, June 2004.
EDMONDS, B.; MOORWOOD, R.; SZCZEPANSKI, R. A. Practical model for effect of salinity on gas formation. In: EUROPEAN PRODUCTION OPE-RATIONS CONFERENCE AND EXHIBITION, 1996, Stavanger, Norway. Proceedings… London: SPE, 1996. Paper 35569
FREIRE, A. F. M.; MENEZES, T. R.; MATSUMOTO, R.; SUGAI, T.; MILLER, D. J. Origin of the organic matter in the Late-Quaternary sediments of the eastern margin of Japan Sea. Journal of the Sedimentological Society of Japan, Fukuoka, v. 68, n. 2, p. 117-128, 2009.
FREIRE, A. F. M. An integrated study on the gas hydrate area of Joetsu Basin, eastern margin of Japan Sea, using geophysical, geological and geochemical data. 2010. 247 f. Thesis (PhD) – University of Tokyo, Tokyo, 2010.
FREIRE, A. F. M.; SUGAI, T.; MATSUMOTO, R. O uso de cinzas vulcânicas para correlações estratigráficas na margem leste do Mar do Japão. Boletim de Geociências da Petrobras, Rio de Janeiro, v. 18, n.1, p. 97-121. nov. 2009/maio 2010.
FREIRE, A. F. M.; MATSUMOTO, R.; SANTOS, L. A. Structural-stratigrafic control on the Umitaka Spur gas hydrates of Joetsu Basin in the eastern margin of the Japan Sea. Marine and Petroleum Geology, Guildford, v. 28, n. 10, p. 1967-1978, Nov. 2011.
FREIRE, A. F. M.; MATSUMOTO, R.; AKIBA, F. Geochemical analysis as a complementary tool to estimate the uplift of sediments caused by shallow gas hydrates in mounds at the seafloor of Joetsu Basin, eastern margin of Japan Sea. Journal of Geological Research, Cairo, p. 1-14, 2012.
HIRUTA, A .; SNYDER, G. T.; TOMARU, H.; MATSUMOTO, R. Geochemical constraint s for the formation and dissociation of gas hydrate in an area of high methane flux, eastern margin of the Japan Sea. Earth and Planetary Science Letters, Amsterdam, v. 279, n. 3-4, p. 326-339, Mar. 2009.
HOROZAL, S.; LEE, G. H.; YI, B. Y.; YOO, D. G.; PARL, K. P.; LEE, H. Y.; KIM, W.; KIM, H. J.; LEE, K. Seismic indicators of gas hydrate and associated gas in the Ulleung Basin, East Sea (Japan Sea) and implications of heat flows derived from depths of the bottom-simulating reflector. Marine Geology, Amsterdam, v. 258, n. 1-4, p. 126-138. Mar. 2009.
HYNDMAN, H. D.; DAVIS, E. E. A mechanism for the formation of methane hydrate and seafloor bottom-simulating reflectors by vertical fluid expulsion. Journal of Geophysical Research: Solid Earth, Richmond, v. 97, n. B5, p. 7025–7041, May 1992.
ISHIZAKI, O. Influence on the marine environment of active methane plumes off Naoetsu, eastern margin of Japan Sea. 2008. 79 f. Thesis (PhD.) – University of Tokyo, Tokyo, 2008.
JOLIVET, L.; TAMAKI, K.; FOURNIER, M. Japan Sea, opening history and mechanism: a synthesis. Journal of Geophysical Research: Solid Earth, Richmond, v. 99, n. B11, p. 22237-22259, Nov. 1994.
KOU, W. W-H.; SMITH, M. A.; AHMED, A.; KUZELA, R. Direct seismic indicators of gas hydrates in the Walker Ridge and Green Canyon areas, deepwater Gulf of Mexico. The Leading Edge, Tulsa, v. 26, n. 2, p. 152-155, Feb. 2007.
KVENVOLDEN, K. A. Gas hydrates as a potential energy resource: a review of their methane content. In: HOWELL, D. G. (Ed.). The future of energy gases. Washington: United States Government Printing Office, 1993, p. 555-561. (U.S. Geological Survey Professional Paper; 1570).
MATSUMOTO, R. Methane plumes over a marine gas hydrate system in the eastern margin of Japan Sea: A possible mechanism for the transportation of subsurface methane to shallow waters. In: INTERNATIONAL CONFERENCE ON GAS HYDRATES, 5., 2005, Trondheim. Proceedings...Trondheim: Torstein Austvik, Statoil R&D Centre, 2005. p. 749-754.
MATSUMOTO, R; OKUDA, Y.; HIRUTA, A.; TOMARU, H.; TAKEUCHI, E.; SANNO, R.; SUZUKI, M.; TSUCHINAGA, K.; ISHIDA, Y.; ISHIZAKI, O.; TAKEUCHI, R.; KOMATSUBARA, J.; FREIRE, A. F. M.; MACHIYAMA, H.; AOYAMA, C.; JOSHIMA, M.; HIROMATSU, M.; SNYDER, G.; NUMANAMI, H.; SATOH, M.; MATOBA, Y.; NAKAGAWA, H.; KAKUWA, Y.; OGIHARA, S.; YANAGAWA, K.; SUNAMURA, M.; GOTO, T.; LU, H.; KOBAYASHI, T. Formation and collapse of gas hydrate deposits in high methane flux area of the Joetsu Basin, Eastern Margin of Japan Sea. Journal of Geography, Indiana, v. 118, n. 1, p. 43-71, 2009.
NAKAMURA, K. Possible nascent trench along the eastern Japan Sea as the convergent boundary between Eurasian and North American Plates. Bulletin Earthquake Research Institute University of Tokyo, v. 58, n. 3, p. 711-722, 1983.
OKUI, A.; KANEKO, M.; NAKANISHI, S.; MONZAWA, N.; YAMAMOTO, H. An integrated approach to understanding the petroleum system of a frontier deep-water area, offshore Japan. Petroleum Geosciences, London, v. 14, n. 3, p. 1-12. p. 223-233, Aug. 2008.
OTOFUJI, Y.; MATSUDA, T.; NOHDA, S. Opening mode of the Japan Sea inferred from the palaeomagnetism of the Japan Sea. Nature, London, v. 317, n. 6038, p. 603-604. Oct. 1985.
SAEKI, T.; INAMORI, T.; NAGAKUBO, S.; WARD, P.; ASAKAWA, E. 3D seismic structure below mounds and pockmarks in the deep water southwest of Sado Island. Journal of Geography, Indiana, v. 118, n. 1, p. 93-110, 2009.
SENO, T. Synthesis of the regional stress fields of the Japanese islands. The Island Arc, Carlton, v. 8, n. 1, p. 66-79, Mar. 1999
SINGH, S. C.; MINSHULL, T. A.; SPENCE, G. D. Velocity Structure of a Gas Hydrate Reflector. Science, New York, v. 260, n. 5105, p. 204-207, Apr. 1993.
SLOAN JR., E. D. Fundamental principles and applications of natural gas hydrates. Nature, London, v. 426, n. 6964, p. 353-359, Nov. 2003.
SON, B-K; YOSHIMURA, T.; FUKUSAWA, H. Diagenesis of dioctahedral and trioctahedral smectites from alternating beds in Miocene to Pleistocene rocks of the Niigata Basin, Japan. Clays and Clay Minerals, Chantilly, v. 49, n. 4, p. 333-346, Aug. 2001.
SUZUKI, U. Petroleum geology of the Sea of Japan, northern Honshu. Journal of the Japanese Association for Petroleum Technology, Tokyo, v. 44, n. 5, p. 291-307, 1979.
TAKEUCHI, A. Recent Crustal Movements and Strains Along the Eastern Margin of Japan Sea Floor. In: ISEZAKI, N. et al. (Eds.). Geology and geophysics of the Japan Sea. Tokyo: Terra Scientific, 1996. p. 385-398. (Japan-URSS Monography Series; v. 1).
TAMAKI, K.; ISEZAKI, N. Tectonic synthesis of the Japan Sea based on the collaboration of the Japan-URSS Monograph Project. In: ISEZAKI, N. et al. (Eds.). Geology and geophysics of the Japan Sea. Tokyo: Terra Scientific, 1996. p. 385-398. (Japan-URSS Monography Series; v. 1).
TOMARU, H.; LU, H.; SNYDER, G. T.; FENH, U.; HIRUTA, A.; MATSUMOTO, R. Origin and age of pore waters in an actively venting gas hydrate field near Sado Island, Japan Sea: interpretation of halogen and 129I distributions. Chemical Geology, Amsterdam, v. 236, n. 3-4, p. 350-366, Jan. 2007.
