globaloccurrencegashydrate kvenvolden&lorenson,2001

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Proceedings o f the Eleventh (2001) International O ffshore and Polar Engineering Conference

Stavanger, Norway, June 17-22, 2001

Copyright © 2001 by The International Society of O ffshore and Polar Engineers

ISB N 1-880653-51-6 (SeO; ISBN 1-880653-52-4 (Vo l. I ) ; ISS N 1098-6189 (SeO

G l o b a l O c c u r r e n ce s o f G a s H y d r a t e

K e i t h A . K v e n v o l d e n a n d T h o m a s D . L o r e n s o n

U . S . G e o l o g i c a l S u r v e y

M e n l o P a r k , C A , U S A

A B S T R A C T

N a t u r a l g a s h y d r a t e i s f o u n d w o r l d w i d e i n s e d i m e n t s o f o u t e r

c o n t i n e n t a l m a r g i n s o f al l o c e a n s a n d i n p o l a r a r e a s w i t hc o n t i n u o u s p e r m a f r o s t . T h e r e a r e c u r r e n t l y 7 7 l o c a li t ie s i d e n t if i e d

g l o b a l l y w h e r e g e o p h y s i c a l , g e o c h e m i c a l a n d / o r g e o l o g ic a l e v i d e n c e

i n d i c a t e s th e p r e s e n c e o f g a s h y d r a t e . D e t a i l s c o n c e r n i n g i n d i v i d u a l

g a s - h y d r a te o c c u r r e n c e s a r e c o m p i l e d a t a n e w w o r l d - w i d e - w e b

( w w w ) s i te ( h t t p : / / w a l r u s . w r . u s g s . g o v / g l o b a l h y d r a t e ) . T h i s si t e h a s

b e e n c r e a t e d t o f a c il i t at e g l o b a l g a s - h y d r a t e r e s e a r c h b y p r o v i d i n g

i n f o r m a t i o n o n e a c h o f t h e l o c a l i ti e s w h e r e t h e r e i s e v i d e n c e f o r g a s

h y d r a t e . A l s o c o n s i d e r e d a r e t h e i m p l i c a t i o n s o f ga s h y d r a t e a s a

p o t e n t i a l ( 1 ) e n e r g y r e s o u r c e , ( 2 ) f a c to r i n g l o b a l c l i m a t e c h a n g e ,

a n d ( 3 ) g e o h a z a r d .

KEY WORDS: gas hydra te , me thane , BSR, resource , c l ima te change ,

geohazard

I N T R O D U C T I O N

Interest in naturally occurring gas hydrate has increased steadily

s ince abou t 1969 whe n V as i l ' ev e t a l . (1970) recogn ized tha t na tu ra l

gas cou ld fo rm gas-hydra te depos i t s tha t shou ld occur g loba l ly

wherev er the p ressu re and tempera tu re cond i t ions a re favorab le .

Recogn i t ion o f the po ten t ia l fo r na tu ra l gas -hydra te occur rence w as

fo l lowed by i ts d iscovery , f i r s t in pe rmafros t reg ions o f no r the rn Russ ia

(M akogo n et al ., 1971, 1972). I t was then obs erved in sediment of the

B lack Sea (Yef rem ova and Zh izhchenko , 1974) and in fe r red by se ismic

surveys to be p resen t in sed imen t o f the B lake R idge , in the wes te rn

Atlantic O cean (Stoll e t a l ., 1971; Ewi ng and Hollister , 1972). By the

ea r ly 1980s, gas hydra te h ad been found in ou te r con t inen ta l marg in

sed imen t o f the Midd le Am er ica T rench o f fshore f rom Mexico

(Sh ip ley and Didyk , 1982) and Gua tem ala (Har r i son and Cur ia le,

1982) . S ince then , the ra te o f d iscovery o f ev idence fo r gas hydra te has

acce le ra ted . The ea r ly h is to ry o f d iscovery o f gas hydra te has been

summar ized by Kvenvo lden (2000) .

E V I D E N C E F O R G A S H Y D R A T E

Three k inds o f ev idence have been used to iden t ify the p resence o f

na tu ra l gas hydra te - -ge o log ica l , geochemica l , and geophys ica l .

Geological evidence includes sediment properties, s tratigraphic

relationships, gas-migration pathways, and, most importantly, the

ac tual recovery and desc r ip t ion o f gas -hydra te samples . Pore f lu

chemis t ry and gas compo s i t ions (molecu la r and i so top ic ) a re im

aspec ts o f gas -hydra te geochemis t ry . F ina l ly , geophys ica l ev ide

includes data from seismic reflection profil ing, seismic refractioangle reflection studies, vertical seismic profil ing, and various k

well- logging . Seismic reflection profil ing is especially valuable

access ing the a rea l ex ten t o f gas -hydra te depos it s . Muc h o f the

geophys ica l ev idence fo r ocean ic gas hydra te i s based on obse rv

of Bo t tom-S imula t ing Ref lec to rs (BSRs) on m ar ine se ismic reco

These anom alous re f lec tions resu l t f rom the acous t ica l d i f fe renc

be tween hydra te -bear ing sed imen ts w i th in the hydra te -s tab i l i ty z

(HSZ) and non-hydra te bea r ing , gassy sed imen t be low the HS Z

(Shipley et al . , 1979).

O C C U R R E N C E S O F G A S H Y D R A T E

A compi la t ion o f g loba l gas -hydra te occur rences was f i r s t und

by Kvenvo lden and McM enamin (1980) . They showed 14 a reas

ocean ic and 5 con t inen ta l ) where geophys ica l and som e geochemevidence ind ica ted gas hydrate . Much o f the geophys ica l ev iden

ocean ic gas hydra te was based o n the obse rva t ions o f BSRs on m

se ismic records . By 1988 the numbe r o f iden t i fied gas -hydra te

had increased to 38 (30 oceanic including inland seas and 8

continental) (Kven volden, 1988). Indepen dently, Panayev (198

Ginsburg et al . (1990) identif ied 22 and 36 regions, respectively

subaquatic gas hydrate occurs. Kv envo lden et al . (1993) l is ted 4

loca tions wor ldwide w here sub-aqua t ic gas hydra te cou ld be exp

and gas -hydra te samples w ere recovered a t 14 o f these loca t ions

International interest in gas hydrate is increasing rapidly with

recogn i t ion tha t the seques te red methane m ay be use fu l a s an en

resource and may be a fac to r in g loba l c lima te change . With th i

increasing interest i t seems appropriate to review the inventory

known and in fe r red gas hydra te occur rences , bo th ocean ic and

continental . There are currently 77 localit ies identif ied globally

geophys ica l, geochem ica l and /o r geo log ica l ev idence ind icates t

presence o f gas hydrate (Fig. 1) . At 23 of these localities, gas-h

samples have been recovered and desc ribed . De ta i l s concern ing

ind iv idua l gas -hydra te occur rences a re compi led a t a new w or ld

web (www) s i te (h~: l lwa lrus .wr .usgs .gov lg loba lhs , d ra te ) . This

has been created to facil i ta te global gas-hydrate research by pro

in fo rmat ion on each loca l i ty where the re i s ev idence fo r gas hyd

Pre l iminary in fo rmat ion fo r th is s i te i s summar ized he re , w i th

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F ig .u re 1 . Map showing w or ldwide loca t ions o f known and in fe r red gas hyd ra te in aqua t ic (oceans , seas, and lakes ) sed imen t and in po la r con t

sed imen t . Open c i rc le s ind ica te loca t ions where samples o f na tu ra l gas hyd rate have been recove red . F i l l ed c i rc le s ind ica te loca t ions o f the in fe

p resence o f na tu ra l gas hyd ra te . Boxes marke d C5-C8 ind ica te a reas in wh ich gas hyd ra te i s in fe r red to occu r .

app rop r ia te re fe rences fo r each gas -hyd ra te occu r rence a t th i s webs i te

(Table 1) .To desc r ibe th is inven to ry , the w or ldwide d i s t r ibu t ion o f gas hyd ra te

has been o rgan ized in to seven reg ions , wi th bas ic in fo rma t ion tabu la ted

in Tab le 1 . The seven geog raph ic reg ions o f gas -hyd ra te occu r rence

a re Pac i fic Ocean , Ind ian Ocean , A t lan t ic Ocean , Nor th (Arc t ic ,

Ocean ic ) , Sou th (An ta rc t ica ) , Othe r ( In land Seas and Lakes ) , andCon t inen tal . At p re sen t the re a re 35 loca t ions in the Pac i f ic Ocean (P 1 -

P35), 3 in the Indian Ocean , (I 1-I3) , 19 in the Atlantic O cean (A 1-

A19) , 3 in the Nor th (Arc t ic Ocean ) (N1-N3) , 4 in the Sou th

(Antarctica) (S1-$ 4), 5 in Oth er (O 1-O5), and 8 in Continental (C1-

C8) . These g loba l loca t ions o f known and in fe r red na tu ra l gas hyd ra te

a re shown on F igu re 1 .

The g loba l gas hyd ra te ww w s i te i s a work in p rog ress . Bes ides

p rov id ing re fe rences to a l l o f the know n gas -hyd ra te occu r rences , the

s i te a lso g ives o the r k inds o f in fo rma t ion such a s abs t rac ts f rom the

re fe rences and techn ica l commen ts . Add i t iona l in fo rma t ion , such a s

4 6 3

se i smic l ines , we l l - logs , geochem ica l measu rem en ts , sample

photographs, e tc . , wil l be displayed at the s i te when available .

A M O U N T O F M E T H A N E

All e s t ima tes o f the me thane con ten t o f me thane hyd ra te a re h

specu la t ive , bu t they sugges t tha t me thane quan t i t ie s a re ve ry la r(Kvenvo lden , 1999). Che rsk iy and Makogo n (1970) p roposed t

amoun t o f m e thane in na tu ra l gas hyd ra te i s po ten t ia l ly "eno rmo

Ear ly e s t ima tes ranged f rom 1 .7 to 4 ,100 exag rams (exa g ram =

o f me thane ca rbon fo r ocean ic sed imen t and f rom 0 .0075 to 18

exag rams o f me thane ca rbon fo r po la r reg ions ( summ ar ized by t

Po ten t ia l Gas Comm it tee , 1981). The S I un i t 'exag ram ' i s u sed

and in l a te r d i scuss ion because i t min imizes the need fo r expone

Because ocean ic gas hyd ra te depos i t s a re much mo re vo luminou

po la r - reg ion gas hyd ra te accumula t ions , the ocean ic gas hyd ra te



Tab le 1. Sum mary of know n and inferred subaquatic gas-hydrateoccurrences in the Pacific, Indian Oceans, and Atlantic Oceans; inpolar oceans and continents; and in inland seas and lakes. [BSR ,

bottom-simu lating reflection; < CI' , low chloride content of pore water;

CH4, high methane content; V AM Ps, velocity amplitude pulldowns;Logs, well-log response; PCS , Pressure core sample; Geophysical,seismic evidence of past occurrence o f gas hydrate]

D e s i g n a t i o n I L o c a t i o n O f f s h o r e i E v i d e n c e

P A C I F I C O C E A NP1 , PanamaP2 Costa Rica (Middle Am erica

Trench)!

P2 [ (DSDP Leg 84) ,,

P2 I (ODp Leg 770)P3 ' Nicarag ua (Middle Am erica

Trench)

P4 Guatemala (Middle Am erica

Trench)!

P4 I (DSDP Leg 67)

(DSDP Leg 84)4

P5

P5

P6

P7

P8

P8

, P8

P 9

~P10

' P l l

I

P12I

, P1 3

P14i

P I5

!

P16i

P1 7

P1 8I P19

P2 0

P2 0

P2 1

P22

P2 3

P24

P24

i P25

i P26

Mexico (Middle America

Trench(DSDP Leg 66)

Mex ico (G ulf of California,Guaym as Basin)

California, USA (Eel River

Basin)

Oregon, USA (Cascadia

Basin)

(ODP Leg 146)

(Hydrate Ridge)

Canada (Cascadia Basin)

(Fjords of Brit ish Columbia)

Alaska, USA (EasternAleutian Trench)

I

Alaska, USA (MiddleAleutian Trench),

Bering,,Sea (Alaska, USA),

(USA, Bering Sea Shelf) .....

(USA/Russia, Navarin

Margin)

(Russia, Shirshov Ridge)

Okhotsk Sea (Paramushir

Island, Russia)

(Sahkalin Island, R ussia)

(off Abashiri , Kitam i-Yam ato Mount, Japan) ,,

Japan Sea (DSDP Leg 57)

(Okushiri Ridge, ODP Leg

127)(W estern Tsu garu Basin ) ..... I

(Tatar Trough)

Japan, Nankai Trough (off

eastern Miyazaki)

(off southern Shikoku)

(ODP Leg 131)

(Muroto Trough)

(Kumano-nada thru of f

Omaezaki Cape)

B SR

B SR

Samples

Samples

BSR

B SR

Samples, < C l "

S a m p l e s , Logs,

<CI"

B SR

Samples

B SR

BSR, Samples

B SR

Samples

Samples

B SR

Slumps

B SR

BSR, <C1-

V A M P s

B SR

B SR

B SR

Samples

Samples

B SR

<C1-

BSR, Sample

B SR

B SR

B SR

B SR

Sample

B SR

BSR, CH4, <C1-

4 6 4

T a b l e 1 c o n t .

D e s i g n a t i o n L o c a t i o n O f f s h o r e E v i d e n c e

P27 Japan, Offshore Chiba BSRBasin

P28 i Japan, Kuril Trench (off BS R

P29

P30

P3 1

P3 1P32

P3 3

Tokachi/Hidaka)

New Zealand (HikurangiTrough)

Chile (Peru-Chile Trench)

Peru (Peru-Chile Trench)

(ODP Leg 1 7)Taiwan (South China Sea)

Australia (Tasman Sea,Lord Howe Rise)

P34 (Timor Trough)

P35 Indonesia (Celebes Sea)

I N D I A N O C E A N

I 1 Oman (Gulf of Oman,Makran Margin)

I2 India (Arabian Sea)

I3 . (Bay ofBen gal )

A T L A N T I C O C E A N

A1 Argentina (Central

A2

A3

A4

A5

A6

A7

A8

A 9

A9

A9

A10

A l l

A12

A13

Argentine Basin)

Brazi l (Amazon Fan)

(Pelotas Basin)

Barbados (Barbados Ridge)

Southern Caribbean Sea

Panama and Colombia(Colombia Basin)

Gulf of Mexico (of fMexico, western area)

(offUSA, northern area)

Southeastern USA (BlakeRidge)

(DSDP Leg 76)

(ODP Leg 164)

Eastern USA (Carolina

Trough),Eastern USA (ContinentalRise)

Newfoundland, Canada(Laborador Shelf)

Norway (Storegga Slide)

A13 , (ODP Leg 104) r

A 14 (Barents Sea) !

A15 (off Svalbard)

A16 (Haakon-Mosby mu d vol. ) .

A17 Ireland (Porcupine Basin) .

A18 Africa (S.W. Africa)

A1 9 , (Nig eria) .,, j

.... NO RTH ( A r c t i c )

N 1 Alaska (Beaufort Sea)

N2 Canada (Beaufort Sea)

N3 ~ Canada (Sverdrup Basin) .

S O U T H ( A n t a r c t i c )

S 1 Antarctica (Wilkes LandMargin)

$2 (Ross Sea)

$3 (Weddell Sea)

$4 (South Shetland margin)

B SR

BSR , CH 4, <C

B SR

Samples

B SR

B S R

CH 4

B S R

B SR

B SR

B SR

B SR

B SR

B S R

B S R

B S R

B SR

B SR

Samples

BSR, Slumps

Samples, <C1

BSR, SampleLogs

B SR

B S R

B SR

BSR, Slumps

<CI"

CH4, < C 1 -

B SR

B SR

Samples

Geophysical

Slumps

Samples

BSR, Slump

Logs

Logs

B SR

CH4, <C1-

B SR

B SR



Tab le 1 con t .

D e s i g n a t io n I L o c a t i o n O f f s h o r e I E v i d e n c e

O T H E R ( IN L A N D S E A S A N D L A K E S )

O 1 Black Sea, Russia

02 Caspian Sea , Russ ia

03 Lake Baika l , Russ ia

• Samples

Samples

BSR, Samples

04 Medi te r ranean Sea (ODP

Leg 160)

05 Turkey (Kula mud volcano)

C O N T I N E N T A L

<CI-, CH4

Sample

C1C2

C3

C4

C5

C6

,

C7

C8

Alaska (North Slope)Canada (Mackenz ie Del ta )

(Arctic Islands)

Russ ia (M essoyakah Fie ld)

(Yiman-Pech ora Province) .

(Western Siberian

Platform)

(Eastern Siberian craton)

(Northeast Siberia)

Logs, PCSSamples, Logs

Logs

CH 4

Interpretat ion

Interpretat ion

Interpretat ion

Interpretat ion

empha sized in global est imates of the methan e content of gas hydrate.

During the late 1980s, est imates of methane in gas hydrate were

greatly constrained when K venvolde n (1988) and MacD onald (1990a),

working independently, est imated the global methane-carbon content

of gas hydrate to be 11 and 12 exagram s, respectively. These nearly

equal est imates are coincidental , but the convergence of independent

ideas made this value, expressed to one significant f igure as 10

exagrams, the consensus est imate.

In the 1990s some new es t imates were made us ing the power of

general circulation mode ls (GCM s) in which p ert inent variables, such

as pressure-temperature phase relat ions, geotherm al gradients, and

sediment porosit ies, are entered into a 1o x 1° global grid (Gornitz and

Fung, 19 94; Harvey and Huang , 19 95). Other global est imates of

methane-ca rbon in gas hydrate were m ade during the same period,

extrapolating from m easurem ents obtained at the Blake Ridge

(Holbrook et al ., 1996; Dickens et al. , 1 997a). In addit ion, e st imates by

Makog on, (1997) and Ginsburg and Soloviev (1998) were based on

theoretical and emp irical information. The est imates published in the

1990s are summ arized in Table 2. The best est imates range from a low

of 0.5 to a high of 24 exagrams. The consensus value of 10 exagram sof methane carbon in gas hydrate worldwide remains about midway

between these extremes.

T a b l e 2. Es t imates made dur ing the 1990s of the amount of methane

carbon [exagrams (10 TMg)] in natural gas hydrate.

E s t i m a t e ( e x a g r a m s ) M e t h o d

R a n g e B e s t

14 to 75 14 GC M 1

15 to 49 24 GCM ~

m

1to 10

- - -3 Ext rapola t ion2

Extrapolation2

8 Theoretical

0.5 Empirical

R e f e r e n c e

Gomitz & Fung (1994)

Harvey & Huang

(1995)

Holbrook et al . (1996)

Dickens et al . (1997)

Makogon (1997)

Ginsburg & Soloviev

(1995)

1GCM, General Circulation M odels

2Extrapolation from one geo graphic area to worldwide est imate

I M P L I C A T I O N S

The global gas hydrate w ww site will also provide discussion with

references to the impo rtant implications of gas hydrate. Gas hydrate

has global importance as a potential (1) energy resource, (2) factor in

46 5

globa l c l imate change , and (3) geohazard . Wi th the inc

wor ldwide in te res t in gas hydra te , ready access to back

informat ion for fu ture research on the g loba l d i s t r ibu t i

significance of naturally occurring gas hydrate is important to

hydrate community.

R e s o u r c e

Methane is the most important energy com ponent in natural ga

a significant port ion of world industry depen ds on m ethane for fu

With i ts large methane content, gas hydrate is a very at tractive po

energy source. Gas hydrate is located within 2000 m of the solid

surface, making this methane tech nologically within reach of the

bit. Although restr icted to polar regions and o uter continental m

gas hydrate is geographically distr ibuted worldwide, mak ing the

methane a possible international comm odity. Meth ane-hy drate 's

energy density (volume of methane at standard condit ions per vo

of sediment) is ten-t imes greater than that o f other unconventiona

sources, such as coal beds, t ight sands, black shales, and deep aqu

it is two- to f ive-t imes greater than the energy density of convent

natural gas, depending on the depth of gas-hydrate occurrence

(MacDonald, 1990b).

Interest in gas hydrate by the energy industr ies has vacil lated o

past 30 years, but interest is presently increasing, especially in th

nations that face or wil l face an energy sho rtage in the near futur

Two countries, Japan and India, have und ertaken major efforts toinvestigate gas hydrate as a potential energy resource. The succe

discovery in 1999 of gas hydrate offshore from Japan, as part of

year study by a Japanese industr ial consortium, is a step forward

direct evaluation of gas hydrate as a p otential energy resource (JN

press release, 2000). I t should be remembe red, however, that dif

scientif ic and technological problems, such as ge nerally poor res

characteristics and d iff icult geographic locations for exploitat ion

be addressed and solved before methane hydrate can ever be used

econom ical source of fossi l fuel (Kvenvolden, 1999).

C l i m a t e

Methane in natural gas not only serves as a com bustible fuel fr

which energy is derived, i t also acts as a greenhouse gas w hen pr

in the atmosphere. Although methan e has a global warming-pote20-times greater than the equivalent weight of carbon dioxide, w

integrated over 100 years, (Shine et al., 1990), its half-life in the

atmosphere is very short, about 10 years. I ts concentration is als

lower than carbon dioxide by a factor of about 160 (Cicerone and

Oremland, 1988). The greenhou se effects of methane in the pres

atmosphere are, therefore, much less than those caused by carbon

dioxide and water vapor. On the other hand, the amo unt of meth

gas hydrate is est imated to be abou t 3000 t imes that in the atmosp

If an appreciable proportion of that methane entered the atm osph

the effect on global temperatures could be significant (MacDo nal1990a).

There has been speculation that methane released from destabil

gas hydrate could affect global cl imate. For example, Nisbe t (19

suggested that methane released from co ntinental gas hydrate cau

warm ing that helped to end the last ice age, and Pau ll et al . (1991

speculated that methan e released from oceanic g as hydrate l imite

extent of glaciat ion during glacial cycles. These scenarios have been proven.

Determining the possible role of gas hy drate in cl imate change

difficult . In fact, just d emonstrat ing the fate of methane from

destabil ized gas hydrate has proven to be elusive. A study test in

hypothesis that gas hydrate in p olar continental shelves is current

decom posing and releasing methan e to the ocean fai led to provid

convincing evidence (Kvenvolden, 19 99). Large excursions in th

carbon isotopic record of carbonate in oceanic sedim ent during th



la test Paleocene (Dickens et al . , 1995; 1997b) provided compelling

ev idence tha t me thane f rom des tab i l ized gas hydra te has a f fec ted the

g loba l ocean ic ca rbona te record . Because i t is uncer ta in i f the methane

and i t s ox id ized p roduc t , ca rbon d iox ide , eve r reached the a tmosphere

to affect radiative properties, i .e. , act as greenho use gases, a l ink to

g loba l c l ima te change has no t been demons t ra ted . Thus , the case

relating gas hydrate and global climate change is st i l l open.

Haza rd

A poss ib le connec t ion be tw een gas hydra te and submar ine s lope

fa i lu re was f i r s t ar t icu la ted by McIve r (1977) . Al though no one has

obse rved these fa i lu res tak ing p lace , the ev idence i s ve ry conv inc ing .

For example , a g ian t co l lapse s t ruc tu re on the B lake R idge (Di l lon e t

a l ., 1998) may have resu l ted f rom the ca tas t roph ic re lease o f gas f rom

destabilized gas hydrate. That the giant Storrega slide offshore from

Norw ay was t r iggered by gas re leased f rom gas hydra te has a t t rac ted a

num ber of adherents (Jan sen et al. , 1987; Bugg e et al. , 1987; Mienert et

al . , 1998). These exa mp les and others strongly support the idea that

gas hydra te i s an impor tan t agen t in modify ing the mo rpho logy o f the

sea f loor and cons t i tu tes a s ign i f ican t submar ine geohazard .

Of the th ree g loba l i s sues posed by gas hydra te - - resource , c l ima te,

and hazard - - the la t ter appears to be the mos t re levan t to hum an

welfa re in the nea r te rm (K venvo lden , 1999) . Th is re levance comes

f rom the fac t tha t humank ind i s exp lo i ting the sea f loor a t eve r -

inc reas ing wa te r dep ths in i t s sea rch fo r new sources o f pe t ro leum-based energy . The p resence o f gas hydra te a t o r nea r the sea f loor

ma kes this interval potentia lly unstable. Such instabili ty can affect

eng ineer ing s t ructu res , such as pe t ro leum produc t ion p la t fo rms and

pipeline installations that are located on the seafloor. Thus, the search

fo r pe t ro leum-based energy sources in the deep ocean i s confounded by

the presence of gas hydrate, but the possibil i ty exists that the

confound ing gas hydra te may la te r p rove to be an energy resource

itsellq

CONC LU S I ON

Natura l gas hydra te i s a g loba l phenom enon now rece iv ing

international attention. I t occurs wor ldw ide but is restr icted to two

env i ron men ts - - in po la r con t inen ta l and deep wa te r (mos t ly on ou te r

con t inen ta l and insu la r marg ins ) sed imen t o f the sha l low geosphere .An inven to ry o f g loba l occur rences show s 77 p laces in which the

presence o f gas hydra te i s in fe r red by geophys ica l , geochemica l , and

geo log ica l me thods . Th is inven to ry inc ludes 23 p laces where samples

o f the subs tance have ac tua l ly been recovered . De ta i l s concern ing

ind iv idua l gas -hydra te occur rences and the g loba l impl ica t ions o f gas

hydra te a re d iscussed a t a new wor ld -wide-w eb (ww w) s i te

(_http:/ /walrus.wr.usgs.gov/globalhydrate) . The potential amo unt of

methane in g loba l gas -hydra te occur rences i s ve ry la rge , wi th cu r ren t

es t ima tes converg ing a t abou t 10 exagrams o f methane ca rbon . In te res t

in gas hydrate is increasing because of i ts potential as (1) an energy

source, (2) a factor in climate change, and (3) a submarine geohazard.

Th is new web s i te has been c rea ted to he lp fac i l ita te g loba l gas -hydra te

research.

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