Tectono-Stratigraphic Control on the Umitaka Spur Gas Hydrates,

1. 1 Tectono-Stratigraphic Control on the Umitaka Spur Gas Hydrates, Joetsu Basin, Eastern Margin of Japan Sea Antonio Fernando Menezes Freire (Petrobras) Luiz Alberto Santos (Petrobras) Ryo Matsumoto (The University of Tokyo)

2. Why we decided to study gas hydrates in Japan? 2 BSRs exist at both Pacific Ocean and Japan Sea margins. Japan Sea Joetsu Basin (study area) Pacific Ocean Nankai Trough Gas hydrates from the northern part of Nankai Trough represent 7 to 14 times the Japanese methane consumption in one year!!! (Fujii et al., 2008). Introduction Source: JOGMEQ

3. The Joetsu Basin gas hydrate study area 3 Study Area Joetsu Basin Methane hydrate has been recognized in Joetsu Basin at Japan Sea since 2004 on both Joetsu Knoll and Umitaka Spur, two ridges located to the south of Sado Island. Introduction

4. 4 • In 2003-2004 the Ministry of Economy, Trade and Industry executed • a 3D seismic survey, and two wells (METI Deep and Shallow) were • drilled in the southern and northern part of Umitaka Spur to explore • deep oil accumulations; Previous studies in Joetsu Basin • An active petroleum • system with oil-bearing • sandy layers was found • from 1000 to 1300 mbsf; • A 15 m oil column was • confirmed in tuffaceous • sandstones at around • 1050 mbsf in the Shiya • Formation. Introduction Saeki et al., 2009

5. 5 • From 2004 to the present, the Department of Earth and Planetary Science • of the Graduate School of Science, The University of Tokyo, in association to • other Japanese institutions and companies has conducted an extensive • exploratory effort to understand the gas hydrate system of Joetsu Basin, • including both Umitaka Spur and Joetsu Knoll; • Extended studies on gas hydrates issues as seafloor topography • (Matsumoto, 2005), geochemistry of sediments (Freire et al. 2009; Freire, 2010), seawater chemistry at plume sites (Ishizaki, 2008), pore water chemistry (Hiruta et al., 2009; Snyder et al., 2008; Tomaru et al., 2007), and acoustic and seismic surveys (Aoyama and Matsumoto, 2009; Saeki et al., 2009; Freire et al. 2010), provide a great knowledge about the gas hydrates of Joetsu Basin. Previous studies in Joetsu Basin Introduction

6. 6 • The special issue of the Journal of • Geography vols. 118 (1) and(5) • highlights state-of-the-art research in • gas hydrates of the eastern • margin of Japan Sea (Matsumoto et al., • 2009). Previous studies in Joetsu Basin Introduction

7. 7 Questions we would like to answer about the Joetsu Basin gas hydrates? Why and how the gas hydrates bubbles are formed in JB? From where the thermogenic gas is coming from? Why the seeps are concentrated over mounds? Why the mounds are aligned? Why the seeps are concentrated in the central part of Umitaka Spur? Is there other hydrocarbon accumulations associated with gas hydrates in JB? Are there potential gas hydrate/free-gas reservoirs in JB? What is the influence of these seeps on the shallow sediments? Introduction

8. The SCS acquisition survey 8 R/V Natsushima Nyquist frequency: 500 Hz Method

9. The SCS acquisition survey 9 • A total of around 196 Km linear was • executed • 26 dip lines (~5 km vs. 0.4 km) • 3 strike lines US23 US19 US08 US51 Method

10. Tectono-stratigraphic control on the gas hydrates of Umitaka Spur The central part of Umitaka Spur is the most fractured and also it is the region where methane seeps and gas hydrate outcrops occur on the seafloor. The anticline shape also induces gas migration to the central part of the spur. 10 US51-strike Results and discussion

11. Tectono-stratigraphic control on the gas hydrates of Umitaka Spur 11 Axial vertical faults in the central part of Umitaka Spur connects deeper hydrocarbon reservoirs to the seafloor, inducing the occurrence of both methane seeps and hydrate outcrops. Mounds and pockmarks are also controlled by the fault distribution. BSR enhanced reflectors US51-strike gas chimneys non-interpreted interpreted Results and discussion

12. Tectono-stratigraphic control on the gas hydrates of Umitaka Spur 12 The central part of Umitaka Spur is the most fractured on both strike and dip directions. non-interpreted interpreted BSR enhanced reflectors US19-dip Results and discussion

13. Tectono-stratigraphic control on the gas hydrates of Umitaka Spur 13 Chaoticzonesare regions where reflectors are not continuous, and were interpreted as debrisflowsdeposits. Note a flatreflectorassociated to debris representing a possible gas/watercontact just below the GHSZ in the western wing of Umitaka Spur. BSR flat reflector enhanced reflectors BSR chaotic zones (debris) US23-dip enhanced reflectors US08-dip Results and discussion

14. Tectono-stratigraphic control on the gas hydrates of Umitaka Spur If proven by drilling wells this is an unconventional free-gas play concept because of the shallow occurrence and the nature of trap and seal caused by the gas hydrate concentration above! On the other hand, the debris in the GHSZ may contain gas hydrate deposits. 14 BSR GHSZ flat reflector ~200 mbsf enhanced reflectors potential free-gas reservoirs potential gas hydrate reservoirs BSR GHSZ chaotic zones (debris) US23-dip potential free-gas reservoirs enhanced reflectors US08-dip Results and discussion

15. Seismic-based map of Umitaka Spur 15 potential free-gas reservoirs A NE-SW trend of faults is observed in Umitaka Spur. These faults are arriving to the seafloor and seems to control the gas chimneys distribution. A NW-SE trend is inferred by Saeki et al. (2009) and Muramoto et al. (2007) using 3D seismic data. The 400 m interval between SCS lines does not promote the identification of small faults and than the NW-SE trend is not observed in SCS. gas chimneys ? ? potential gas hydrate reservoirs fault system Results and discussion

16. Gas hydrates occurrence • and distribution of • Umitaka Spur are • controlled by: • Axial fracturing and faulting • system • Anticline convex shape • Carrier beds and • boundaries; • Hydrocarbon migration • from deeper reservoirs. 16 Arrows indicate the predominantly gas migration pathway; Gas migration is focused on the axial zone because of faults, anticline convex shape and carrier beds and boundaries. US19 Results and discussion

17. 17 THANK YOU for your attention! For additional information: Freire, A.F.M., Matsumoto, R., Santos, L.A. (2010). Structural and Stratigraphic Control on the Umitaka Spur Gas Hydrates of Joetsu Basin in the Eastern Margin of Japan Sea. Journal of Marine and Petroleum Geology (accepted on September, 2010).