Vành đai khí hydrate ở tây thái bình dương

WESTERN PACIFIC GAS HYDRATE BELT Renat Shakirov Russian Academy of Sciences V.L 11'ichev Pacific Oceanological Institute 43 Baltiyskaya Sir., Vladivostok, 690041 RUSSUN FEDERATION ren@

WESTERN PACIFIC GAS HYDRATE BELT

Renat Shakirov

Russian Academy of Sciences V.L 11'ichev Pacific Oceanological Institute

43 Baltiyskaya Sir., Vladivostok, 690041

RUSSUN FEDERATION ren@poi.dvo.ru

Abstract:

Western an eastern margins of Pacific Ocean presents numerous gashydrates sites, distributed as Gashydrates Provinces (referred to the sea's title) which can be combined to Circum Pacific Gashydrate Belt Gas (mainly methane) hydrates accumulation induced by varies active geological features determined by geodynamic and tectonic type and seismic stale's of Pacific and adjoining lilhosphere plate's borders Bering Sea, Okhotsk Sea, Japan Sea, East-China Sea, East Vietnam Sea, Celebes and Sulu Seas and southward to New Zealand offshore presents Western Pacific Gas Hydrate Bell and exposed methane hydrates distribution in sediments Hydroacoustic, seismics, coring were a prime methods applied to gashydrate searching and exploration Methane hydrates was explored since 88-th (Okhotsk Sea) Gas hydrates supplying fluid within the thick Cenozoic sediment basins (up to 10 km thickness) are linked lo multiple hydrocarbon accumulations: mainly oil and gas deposits, and gas (methane) hydrates -proved for the Bering, Okhotsk and Japan Seas Submarine gas seepage usually accompanied by contrast seismic and acoustic anomalies in the sediments and water column (e.x up to 700 gas "flares" prior to 2010 indicates gas hydrate fracture type accumulation in western Okhotsk Sea) High hydrocarbons were found as well, but methane is dominated everywhere Methane sources discussed as mixture of thermogenic and biogenic origin Gas hydrate occupies mainly 20-45% of pore volume BSR was found globally, but this border means not gas hydrate stability zone only Methane resources trapped in Western Pacific gas hydrates belt estimated based on latest investigations at least for 5x10* cubic meters Keywords: Pacific Gas Hydrate Belt, gas hydrates Pacific Ocean, active

margin, oil-gas deposits

INTRODUCTION

The purpose of article is fiirther developing the geological point of view to submarine gashydrate occurence For the last 50 years nice explorations toward gas hydrate occurence were conducted by international scientific and petroleum community (Ginsburg and Soloviev, 1994; Sloan, 1998; Suess et al., 1999; Max, 2000; ODP Legs; Mallik Production Well and many other research) Geophysical,

Renat Shakirov

and geochemical gashydrates features were studied deeply and allow us to conduct present work Authors also participated in gas hydrate projects personally for last

15 years (Okhotsk and Japan Seas)

Numerous gashydrates findings (Fig 1) dictates ological zoning of this phenomena Gas hydrates founded circum around the Pacific Ocean Margins on the water depth from 300 (Okhotsk Sea) to 2000 meters (Gulf of Mexico) and even 2,800 m (Bering Sea) The hydrate stability zone linked to the depth-pressure and temperature are actually vary from 300 to 1500 meters and cover huge horizontal areas Direct sampling and drilling extent in situ gas hydrate presence from year to year At the same time, we have to note, that BSR is just useful! seismic feature, which can not warranty the fact of hydrates occurence In some seas, such as Okhotsk, Japan Sea, BSR can reflect also sediment transformation border (e.x opal

CT - cristobalite) and stratigraphy borders Modelled gas hydrates distribution

show same promising areas (Fig 2) as in situ data

The Pacific Ocean encompasses approximately one-third of the Earth's surface, having an area of 179.7 million square kilometers - larger than Earth's landmass entire In that case any widely distributed natural phenomena in Pacific Ocean (high seismicity, volcanic activity, oceanological features et cet.) has significance influence on environment realm Extending approximately 15,500 kilometers (9,600 miles) from the Bering Sea in the Arctic to the northern extent of the circumpolar Southem Ocean at 60° S Along the Pacific Ocean's irregular westem margins lie many seas (from subarctic to tropical conditions, mostly with very high sedimentation rates) and originated on destructive oceanic and continental crusts: Bering Sea, Okhotsk Sea, Sea of Japan, East China Sea, East Vietnam Sea, Yellow Sea, Coral Sea, Philippine Sea, Celebes Sea, Sulu Sea and Tasman Sea In the nortii, the Bering Strait connects the Pacific with the Arctic Ocean Gas (methane) hydrates considering as a future altematively fossil resources continuously investigating in Westem Pacific since 80-th One of the fu^t gashydrate fmdings was in 34 Cruise of RV "Morskoy Geophysic"'(Dr A Obzhirov, Russia, POI FEB RAS, 1988) in the Okhotsk Sea Gas hydrate bearing sediments were recovered by gravity corer and methane- flux registered in that scope by echosounder on 700 m water depth

Fig 1 Worldwide gas hydrate occurrence I - recovered; 2 - hydrate sediment signs with methane leakages; 3 - inferred; 4 - potential (by BSR and geochemical anomalies)

Votum*{»10 111-)

Fig 2 Modeled gas hydrates distribution in World Ocean (Klauda J.B., 2011) Since numerous fmdings of submarine gashydrates and growing their fiittire energy source rate we can conclude that gas (methane) hydrates can be considered

as new fuel minerals In an agreement to applied geology, minerals, which found closely on area can be combined; areas to provinces, and, if enough fundamentals Provinces belonging to same global linear structure can be presented by Belt Westem Pacific (as well as Eastem Pacific) both presented by corresponding Gas Hydrate Belts, which has own different form each other geological features The westem Pacific Ocean is almost totally controlled by subduction zones Mechanical coupling between the downgoing and overriding plates along continent margins bounded by thick sediment strata (up to 10 km) resulted in hydrocarbon prone gas basins Several hundred active volcanoes that sit above the various subduction zones also dictates enhanced hydrocarbons maturation by deep fluid supply Only the Antarctic and Australian coasts have no nearby subduction zones Hydrates occurrence in westem Pacific were studied on and below the seafloor if the water temperature and pressure falls within the stability zone (depths range from 300 m

in Okhotsk Sea and inferred on 3800 m in Bering Sea) and methane saturated fluid upraised to the sea floor Bearing sediment rocks contains hydrates as dispersed in rock pores, or form nodules, layers or massive aggregations Most of gas hydrate findings belong to Quatemary sediments, presented by silt, clayey silt, sand and their mixtures Deep gashydrates on 200-500 and more meters (primary gas hydrates?) inferably occurs in Tertiary sediments

RESULTS AND DISCUSSIONS

Follow from high latitudes to southem seas of Westem Pacific, geological review exposed evidences for neighboring gas hydrate provinces referred to the sea's and their conjuction to the Gas Hydrate Belt Although no representative aggregates of gas hydrates were recovered in Bering Sea (Fig 3), gas hydrate potential of this province is evidently very high The deep Aleutian and Bowers Basins lie, at approximately 3,600- to 3,900-m water depth Assuming that thousands of VAMPS and other gas stmctures might contain up to 2*10' cubic meters of methane (Scholl et al., 2007)

h , ^An&BeMa ^

jA

0 m

Fig 3 Bering Sea, North Pacific Ocean Bathymetric contour lines are in meters, with the darkest line representing

3,500-m water depfli Star, location of VAMP example; circled stars, nearest drilled wells, from Deep-Sea Drilling Program (DSDP) leg 19 Track lines (gray) represent approximately 24,000

km of digitally recorded USGS single-channel seismic data After Scholl et al., 2007

One of the most prominent gas hydrate province was found in second largest

margmal sea of the Pacific Ocean - Okhotsk Sea Submarine metiiane hydrates

were explored mainly by the sediment sampling (coring, dredging, grabbing) Sediments and water column were deeply investigated for geochemistry,

sedimentology, stratigraphy etc Methane leaking to the seawater from the active gas venting sites within the thick Cenozoic sediment basins (up

to 10 km) bearing multiple hydrocarbon accumulations: oil and gas deposits (Kharakhinov, 1998), gas (methane) hydrates (Obzhirov, 2004; Shakirov et al., 2005) and from coal bearing strata 2 areas were evidently supply by gas hydrates: north-east slope

of Sakhalin Island and north-west slope of Paramushir Island Methane is the dominant GH gas, generally comprising 99.9% of the total hydrocarbons and referred to structure 1 We recovered gas hydrates up to 35 cm thick pieces by hydrocoring Hydrocorer could not penetrate through the gashydrate layer and breaked off a piece only Fracture type of gashydrate accumulated mainly within the cross sections of faults

CD-'CZI-'EI-'IXI-

lEi-lT3-"lS3-'lXl-Fig 4 Geological state of the North East Sakhalin

Slope Legend: 1,2,3 - density of the hydrocarbon

generation (see Fig 5); 4 oilgas deposits; 5

-methane vent/flares; 6 - -methane hydrate findings;

7 mud volcano; 8 rift zones; 9 isopachits; 10

-isobaths; 11 - tectonic fauhs; 12 - methane hydrate

province proposed in 2005 and confirmed in

southem part in 2009-2010

Renat Shakirov

Prior to 2005 the distribution of gasgeochemical anomalies (up to 1200 nmol/1), newest findings of flares and methane hydrates (Shoji et al., 2007-2010) has interested author conduct certain review of geological state of north-eastern Sakhalin slope Thus, analyses of hydrocarbon production in sediments up to

10-20*10' t/km- (Gretskaya el al, 1992), stratigraphy and favorable lithology of

sediment strata up to 3-5 km, rift systems, suitable water pressure 400-1500 m and temperature of near-bottom water +2°C, BSR distribution and heat flux studied in detail in the scope of KOMEX Project (Ludmann and Wong, 2003), recent

tectonics pattern (Kharakhinov, 1998; Baranov et al., 1999; Bogdanov and Khain,

2000) allowed us to forecast an occurrence of methane hydrates in Derugin Depression much widely (up to 4,500 km^ about) and especially toward south from known GH findings Examination of this methane hydrate province by an additional geological field studies was conducted in 2009-2010 and that scopes confirmed our prognoses for southward area extension: at present, methane hydrates proved during 2009-2010 by direct methods at least for 7,000 km^ Additionally, micro-gashydrate cement was found in fine sediments in southem part of East-Sakhalin Gas Hydrate Area Based on direct coring and BSR methane resources in Okhotsk GH Province estimated for2xlO'^ cubic meters In compare, total World traditional reserves of natuarl gas estimated 187x10'^ cubic meters (IEO20I0 Reference case, 2010)

The pesence of substantial deposits of methane hydrates in both around Japan and South Korea has been confirmed, and both countries are investigating how those resources could be safely and economically developed Sources of methane

in Okhotsk Sea gas hydrate province are both thermogenic and microbial with 5C"-CH4-31,7 77,5 %cPDB

In Japan Sea methane hydrates were found mainly around the Honsyu and Hokkaido Islands The promising massive gas hydrate deposit was deeply studied near the Sado Island (Matsumoto R., 2008) There in, from METI-Sado exploratore well (2004) was clearly showed evolution of uprising thermogenic methane 5 C ' -CHj -32 %oPDB from 2000 mbsf to gas mixture of biogenic-thermogenic gas resulted m 8C "-CHj -60 96oPDB The next famous gas hydrate province is accretionary prism on pacific side offshore Honsyu Island, controlled by Japan subduction zone Gas resource potential in Eastern Nankai Trough GH deposits equivalent of 14 years domestic demand of gas (Tanahashi, 2011), and production testing have been started In this area methane hydrates mostly fill the pore space in predominamly sand sediment strata ODP also e;caminated this province (Leg 190) Although, as a rule, no solid gas hydrate was recovered during drilling, their presence was documented indirectiy for depth 100-500 mbsf Both temperature measurements of cores on the catwalk (4-6 °C lower than background), pore fluid

CI minimum (517 mM at BSR depth 420 mbsf) and methane high content, indicate the existence of gas hydrates at slope (e.x Site 1176 and Site 1178) Recovery of solid hydrate is unlikely unless it is extremely abundant Total inferred resources around Japan estimated lO'^-lO" m' (Tanahashi 2011)

108 i;^

TTT-In eastem waters of Korea gas hydrate was recovered using piston corer (KIGAM, 2007) And gas hydrate drilling expeditions in Ulleung Basin (UBGH) was performed as a part of Korean National Gas Hydrate Program During that program massive methane hydrates were recovered by drilling (fig 5)

Fig 5 Gas hydrate from Ulleung Basin (Chun et al., 2011)

In some areas gashydrate not studied by dkect methods, but gashydrate promissing sediment environment was examinated usmg the BSR distribution and its sub-bottom depth According to this, the t tai volume of the hydrate stability field of offshore southem Taiwan (sub-bottom depths 300-600 m) associated witii free sediment sequences Q1-Q2-Q3 estimated 18062 cubic meters (Chi et al., 2006) In addition, scientists estimate the total pore space in the sediments of the hydrate stability field in total to be 8308 cubic km for all BSR Authors resonably concern that these estimates can be used to derive the total hydrate storage in the Taiwan region once better understandings of the regional porosity-depth pattern and saturation values of the hydrates in the sediments offshore of southem Taiwan Also, we have take into considerations that BSR not warrants the gas hydrate presence For example, explorations around India clearly shows that drilling through the BSR promissing GH areas can failed - no hydrates were found in few drilling sites

Southward Japan Sea and Korean seas gashydrate occurrence studied poorly compared to northen areas, but these part of Westem Pacific GH Belt has also numerous signs of gas hydrates and some direcrt fundings were recovered also Some areas have lowest hydrate resources, but large oil-gas reserves, such like Yellow Sea Yellow Sea is lower promising for gas hydrates accumulation since water depth not exceeds 160 m Nevertheless, Guangzhou Marine Geological Survey Bureau discovered stiTictures favorable to oil/gas accumulation in the depression basin in the north of the South Yellow Sea The survey analysis and comprehensive evaluation show that oil/gas resources in the South Yellow Sea are around 2.0-2.8 billion tons, indicates large oil/gas exploration province (Wang, 2001)

By the way, at least 27 big stmctures as promissing basins, troughs and ti-enches are locate in South-East Asia (Wilde and Quinby-Hunt, 1997) Sill depth of these stmcters wary from 400 (Sulu Sea) to 3130 meters (Talaud Trough, Banda Basin) and in average 2300 m Water depth in these stmctures ranged 1590 (BaU basin) to

10500 (Mindanao Trench) and in average 4550 meters bss Fore temperature of near bottom water layer +5 degrees Celsium, clathrates on the floor of the bsasins from 800 meters to about 1700 meters would become dissosiate Thus, these

Renat Shakirov

structers can contain gas hydrates if methane content and sediment features are favorable

In East China Sea inferred gas hydrate sediments was found southward Kyushyu Island

In East Vietnam Sea, gas hydrates were evidently proved in northern sea's area (Wu, 2011) Here the deep gashydrate signes were obtained by drilling in northern South-China Sea for 170-230 m bsf (Wu, 2011)

In Celebes Sea gas hydrates promising province expected by geophysical and geochemical anomalies (Fig 1), but needs deeply application of hydrate safety direct methods

Most southern gas hydrates in western Pacific was evidently sampled in Hikurangi gas hydrate province Channel systems considered to be potential sand dominated gas hydrate reservoirs (Pecher and Fohrmann, 2011) Fig 6 Circum Pacific Gas Hydrate Belt

WPGHB - Western Pacific Gas Hydrate Belt;

EPGHB - Eastern Pacific Gas Hydrate Belt;

BSGHP - Bering Sea Gas Hydrate Province 1

- Circum Pacific Gas Hydrate Belt.; 2 - inferred

hydrates (examples); 3 potential GH sites

(examples)

CONCLUSIONS

It is reasonable to suggest offshore gas hydrate zoning from

GH Areas to GH Provinces and, , , , ^ , „ finally to GH Belts We can clearly subdivide Westem Pacific GH Belt belongs to active margin, and Eastem Pacific GH Belt belongs mainly to passive state of continents margin Conjunction

of these Be ts on Bering Gas Hydrates Province can illustrate Circum Pacific Gas Hydrate Belt (Fig 6)

The distribution of gas hydrates are related genetically with hydrocarbon accumulations, spatially with local structures, and controlled particularly by active faulting belongs to transform plate's borders, especially subduction zones Fracture type gas hydrate sediments filling mainly found there in (massive gashydrates)

h v r i t ? / f i i r ™ ' L ' ' " " " ' / ' ° " ^ "'^ subduction zones considered lithology gas

a C i ^ i t h f l^'^Pu'T" ^^ ''^''''"">- "^""^"^ high seismic activity cause fauK's

sedhlenK^l'i!!'''' " ^ / " " l * ' ' " ' '^'"'•^'^'' " " ' ' ' s migrate through the upper

d e f Z a L n f f , f " n c o " '^' ''^ ^°°'' particularly via the flult systems,

deformations of the BSR, mud volcanoes, gas-geothermal springs, and

pockmark-like structures are originates and gas hydrate is the most significant manifestation

of future combustible minerals

Methane origin is presented by mixture of thermogenic and biogenic gases Gas

hydrate occupies up to 45% of pore volume in sediments BSR was found globally,

but this border means not gas hydrate stability zone only and not means

everywhere gashydrates occurrence

Methane resources trapped in Westem Pacific Gas Hydrates Belt can be

estimated based on latest investigations at least for 5x10*" cubic meters

Unfortunately, drilling programs not yet covered all offshore promising

continental and islands margins It is very important to confirm hydrate resources

by direct drilling Still present time the IEO2010 Reference case does not include

methane hydrate resources in its estimates of natural gas resources, and the

development of gashydrates examinations on a commercial and ecology scale is

most important to enhance govemmental participation

ACKNOWLEDGEMENTS

Authors would like to thank the German-Russian Cooperation in KOMEX

project (1998-2004), Russia-Japan-Korea CHAOS (2003-2006) and SSGH Projects

(2007-2012) This research was supported by NP "Global Energy Prize"

(MG-2010/04/6); grant of Far Estern Branch of Russian Academy of Sciences

(09-I-P17-10) and by Russian State Programm "World Ocean" Authors express sincere

gratitude to all colleagues for the important and constructive comments which

benefited this work significantly

We also appreciated for collaboration with Dr Tsunogai Ummu (Hokkaido

University) who conducted advanced mass-spectrometry on our gas samples

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