801

137°58' 138°00' 138°02' 138°04'

37°24'

37°26'

37°28'

37°30'

37°32'

0 1 2

km

METI_S well

US-08

US-19

US-

51 METI_D well

US-07

US-23

US-03US-04US-05US-06

US-09

US-10

US-11US-13

US-15

US-17US-16

US-18

US-20US-22

US-25US-26US-27US-28

US-29

US-

53

US

-54

JK/US-108

JAPAN

Pacific Ocean

500 km

128°E 130°E 132°E 134°E 136°E 138°E 140°E 142°E32°N

34°N

36°N

38°N

40°N

42°N

44°N

Sendai

Akita

Tokyoa

Niigata

Kanazawa

e

e

i

100 km0

Umitaka Spur

Japan Sea

KOREA

Hiroshima

Sakata

Hokkaido

Nagazaki

Sapporo

Honshu

Joestu Basin

Sado Island

Joetsu

ShikokuKyushu

CHINA

UMITAKA SPUR

NORTH

UMITAKA SPUR

CENTER

UMITAKA SPUR

SOUTH

-100

0m

-110

0m

-1100m

-1100m

-900

m

Gentle

Slope

Steep

Slope

Depression (pockmark)

Mound (seep)

Mound (seep)

Depression (pockmark)

-1000m

-900m

-1000m

-1100m

Contour interval = 5m

continental slope

FIG

. 03

FIG. 05a

FIG. 05b

FIG. 04

-47‰ δ13CCH4

-54‰ δ13CCH4

-89‰ δ13CCH4

-99‰ δ13CCH4

-67‰ δ13CCH4

Figure 1: Location map of Umitaka Spur. Map of the seafloor relief showing mounds and pockmarks in a NE-SW trend. Stars indicate plume/seep sites. Open circles indicate carbon isotope analyses of mud-gas, suggesting thermogenic originat the central part of the spur. The 2D single channel seismic survey is shown.

METI DEEP WELL (Proj.) METI SHALLOW WELL (Proj.)1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

TW

T (s

)

US-51

0 1Km

Haizume Fm.Seafloor

S N108

BSR

EnhancedReflectors

(2b)

Debris Flow

Debris Flow

H-IH-IIH-IIIH-IV

H-VH-VI

Umitaka SpurSouth

Umitaka SpurCentral

Umitaka SpurNorthl

METI DEEP WELL (Proj.) METI SHALLOW WELL (Proj.)1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

TW

T (s

)

US-51

0 1Km

Haizume Fm.Seafloor

S N03 06 07 08 09 2654 28 29 108

BSR

EnhancedReflectors

GasChimney

(2b)

Debris Flow

Debris Flow

Nishiyama Fm.

H-IH-IIH-IIIH-IV

H-VH-VI

Umitaka SpurSouth

Umitaka SpurCentral

Umitaka SpurNorthl

Depression (pockmark)Mound (seep)

Depression (pockmark)Mound (seep)

GasChimney

Zoom area for fig. 3

Zoom area for fig. 3

Final Depth: 1027 mbsf ( 2.5 s TWT)Final Depth: 2088 mbsf (3.3 s TWT)

Nishiyama Fm.364 mbsf (~1.3 Ma)

Nishiyama Fm.622 mbsf (~1.3 Ma)

10 13 15 18 1917 20 22 23 2511 16 270405

03 06 07 08 09 2654 28 2910 13 15 18 1917 20 22 23 2511 16 270405

Figure 2: Near-strike SCS profile US-51. Note mounds and pockmarks at the seafloor in the central part of the spur, where fracturing is more intense.

Top of Nishiyama Fm.

BSR

EnhancedReflectors

GasChimney

GasChimney

GasChimney

SW NE

mound seep site

H-VI

H-V

H-IV

H-III

H-IIH-I

pockmark US-511.2 -

1.4 -

1.6 -

1.8 -

2.0 -

TW

T (s

)

10 13 15 18 19

- 1.2

- 1.4

- 1.6

- 1.8

- 2.0

TW

T (s

)

SW NE

17 20 22 23 2511 16 10 13 15 18 1917 20 22 23 2511 16

0 500m0 500m

??

Figure 3: Detailed image of the near-strike SCS section US-51 shown in figure 2. Reflectors H-I to H-VI can be observed and correlated in all SCS sections. Note that faults link deep parts of the spur below the top of Nishiyama Formation to the seafloor and to the GHSZ, where offsets are observed. Pink dashed line is the potential BSR.

EnhancedReflectors

BSR

mounds seep site

1.2 -

1.4 -

1.3 -

1.5 -

TW

T (s

)

US-19

“pull-up”

gaschimney

offset

W EW E

0 500m 0 500m

54 54

1.6 -

?

Figure 4: Detailed image of dip section US-19 showing pull-up structure within gas chimneys inside the GHSZ. Note that the seismic events, BSR and enhanced reflectors are offset by gas chimney boundary faults.

BSR

EnhancedReflectors Fluid

Contact(Flat-Spot)

CahoticZones

Free Gas?

Water

Enhanced Reflectors

BSR

Debris Flows

CahoticZone

Debris FlowsCahotic Zones

Debris Flows

Debris Flows

Debris Flows

FluidContact

(Flat-Spot)

H-III

H-II

H-IV

H-IV

H-III

H-V

H-II

W E

US-231.5

1.7

1.6

1.8

TW

T (s

)T

WT

(s)

US-081.5

1.7

1.6

1.8

0 500m

53W E

W E W E

0 500m

0 500m

0 500m

(a)

(b) 53 53

53

Figure 5: Detailed image of dip SCS profiles US-23 and US-08. Chaotic zones are zones where reflectors are not continuous, and are here interpreted as debris-flow deposits. Note a flat reflector (light blue dashed line) associated to the debris representing a possible gas/water contact just below the BGHSZ on the western flank of Umitaka Spur. In this case, gas hydrates above represent a seal for a shallow free-gas accumulation below.

GW

?

? ?

H-IVH-V

H-VI

H-IH-IIH-III

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

TWT

(s)

5351 54US-03METI DEEP WELL

Final Depth: 2088 mbsf (3.3 s TWT)

Water Depth: 885 m

continental

slope

0 1Km

W E

Haizume Fm.Seafloor

Debris-Flow

Nishiyama Fm.622 mbsf (~1.3 Ma)

Umitaka Spur South

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

TWT

(s)

5354 51US-29

0 1Km

Water Depth: 971 m

METI SHALLOW WELL

Final Depth: 1027 mbsf (2.5 s TWT)

W E

BSR

EnhancedReflectors Fluid Contact

(Flat-Spot)

(3a)

Debris Flow

Debris Flow

H-IH-II

H-IIIH-IV

H-VH-VI

Haizume Fm.

Nishiyama Fm.364 mbsf (~1.3 Ma)

Seafloor

Umitaka Spur North

(3b)

Figure 6: Dip SCS profiles US-29 and US-03, respectively at the northern and the southern part of Umitaka Spur. METI Deep and Shallow wells are plotted. See figure 1 for location of profiles and wells.

H-I

H-II

H-III

H-IV

H-V

H-VI

?

??

??

?

gaswater

gaschimney

pull-up enhanced reflectors

BSRseafloorHaizume Fm.

Nishiyama Fm.

moundseep site

1.2 -

1.4 -

1.6 -

1.8 -

2.0 -

2.2 -

2.4 -

TWT (

s)

W E

W E

1.2 -

1.4 -

1.6 -

1.8 -

2.0 -

2.2 -

2.4 -

TWT (

s)

0 1Km

US-013

0 1Km

535451

535451

US-013

debris

debris

Figure 7: Dip SCS profile US-13 located on the central part of Umitaka Spur. Note strong gas chimney with blanking hiding weak reflectors. Pull-up structures within the gas chimneys affect both seismic events and the BSR.

? ??

Debris-Flow

Occurrence Area

(projected)

Free Gas

Target

Below

BSR

(projected)

801

137°58'

137°58'

138°00'

138°00'

138°02'

138°02'

138°04'

138°04'

37°24' 37°24'

37°26' 37°26'

37°28' 37°28'

37°30' 37°30'

37°32' 37°32'

0 1 2

km

JOET

SU-U

MITAKA TR

OUGH

UMITAKA SPUR

NORTH

JOETSU KNOLL

SOUTH

UMITAKA SPUR

CENTER

UMITAKA SPUR

SOUTH

Gas Hydrate Target (projected on the seafloor)

Gas Chimney (seafloor)

Normal or Vertical Faults (seafloor)

1

Assimetrical Anticline Axis

Transfer Zone Mound Seep Sites

-100

0m

-1000m

-110

0m

-1100m

-1100m

-900

m

Seafloor Lineaments

BSR Area

(Projected)

Debris-Flow

Occurrence Area (projected)

Free-Gas Occurrence

Area (projected)

BSR Area (projected)

continental slopeBORDER FAULT

Figure 8: SCS-based map of Umitaka Spur. Deeper features are projected on the seafloor. A NE-SW trend of faults is observed. These faults connect to the seafloor and seem tocontrol gas chimneys distribution.

potentialfree-gasreservoir6x107 m3

0,001 TCF(free gas)

potentialgas hydratereservoirs

4x108 m3

0,007 TCF(gas hydrates)

0

200

0 1Km

W E

BSR

Fluid Contact

Debris Flow

Debris Flow

Depression (pockmark)Mound

Gas ChimneyEnhanced

Reflectors

Nishiyama Fm.

100

300

400

500

mbsf

Water Depth ~ 900m

Free Gas? Water

TW

T (s

)

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

US-19

Gas Chimney

H-IH-II

H-III

H-IV

H-V

H-VI

Free Gas?

Giant Plumes

Deep Oil/Gas Reservoirs and Source Rocks(>1000mbsf)

Carrier Beds (low methane flux)Carrier Beds

Faults and Fractures (high methane flux)

Base of the Gas Hydrate Stability Zone

Potential Thermogenic Gas Hydrate Zone

SeafloorMud Gas Analysisδ13CCH4 < -60‰

Seafloor Mud Gas Analysisδ13CCH4 < -60‰

Mud Gas Analysisδ13CCH4 > -60‰

Concentration of Methane Seeps and Gas Hydrate Seafloor Outcrops

Structural and Stratigraphic Gas Focused Model

Figure 9: Model for gas hydrate occurrence and main features of the Umitaka Spur gas hydrate/free-gas system, based on dip profile US-19, crossing the axial part of the structure in a W-E direction. H-I to H-VII are seismic events mapped along the SCS profiles within the Haizume formation. Orange areas represent debris-flow deposits. Arrows indicate potential gas migration pathways along faults, fractures and carrier beds. The arrow size represents the migration intensity.

Methane / Gas HydrateBubbles

MoundMound

Pockmark

Holocene

mound flank

Pre-Holocene

Pre-Holocene

GasChimney

0m

1m

2m

3m

Gas Flux

seep site

Holocene Holocene

mound flank

gas hydrate zone

Figure 10: Migration model for the formation of mounds. During gas hydrate dissociation and direct gas migration along faults from deeper reservoirs, LGM or older sediments are uplifted and exposed on the seafloor. The hypothesis is that the exposure of old sediments is caused by an increase in the pore-space volume that induces an uplift of pre-Holocene sediments resulting in seafloor mounds. This process is still going on at the present time. On the seafloor the younger sediments were washed away by near-seafloor ocean currents. Note that methane bubble seeps are located over mounds at the seafloor, and piston-cores collected from the top of the mounds can recover only pre-Holocene sediments, while those located at the mound-flanks can also recover Holocene sediments.

An Integrated Study on the Gas Hydrate Area of Umitaka Spur, Joetsu Basin, Eastern Margin of Japan Sea, using Geophysical, Geological and Geochemical Data

Antonio Fernando Menezes Freire Ryo Matsumoto Petrobras Research Center (CENPES) The University of Tokyo

fernandofreire@petrobras.com.br ryo@eps.s.u-tokyo.ac.jp

We used 2D single channel seismic (SCS) data to understand the structural-stratigraphic control on the gas hydrates of Umitaka Spur, an anticline located at the eastern margin of the Japan Sea. On the other hand, sedimentology, stratigraphy and geochemistry of sediments collected by piston- and push-cores, provide us the tools to understand what is happening at the seafloor in areas with gas hydrates and methane seepages. Chimney-like structures seem to be strongly controlled by a complex anticlinal axial fault system. In some of them, SCS profiles show high amplitude events with pull-up structures, probably due to massive and dense accumulation of gas hydrate. A BSR is recognized within gas chimneys and in the eastern flank of the structure. The anticlinal axial fault system, the convex shape of the spur, and permeable layers as conduits induce gas migration to the top of the spur, providing strong seepages and giant plumes in the sea water column. Geochemistry of sediments enabled the characterization of background signatures and the origin of the organic matter of both Holocene and LGM sediments, on the basis of δ13Corg, TOC/TN ratio. The geochemical signatures of the seep site sediments are similar to those of the deeper LGM sediments. Anomalous features of seep sites seem to imply migration of sediments as well as water and gas. Gas hydrates cause an increase in the sedimentary volume, inducing the formation of mounds with older and deeper LGM sediments on the seafloor.

Poster section 1: Natural Gas HydratesPoster 5 Monday, 18th July 10:45~12:30

For additional information, a full paper is available on line at Science Direct:Freire A.F.M., Santos L.A., Matsumoto R. (2010). Structural-stratigraphic control on the Umitaka Spur gas hydrates of Joetsu Basin in the eastern margin of Japan Sea. Marine and Petroleum Geology, Special Issue about Gas Hydrates (in press), doi:10.1016/j.marpetgeo.2010.10.004