surface and subsurface manifestations of gas movement through a n-s transect of the gulf of mexico ...

8/12/2019 Surface and Subsurface Manifestations of Gas Movement Through a N-S Transect of the Gulf of Mexico Whelan H

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Surface and Subsurface Manifestations of Gas Movement Through

a N-S Transect of the Gulf of Mexico

Jean Whelan 1, Lorraine glinton1, La!rence "athles ###$, Steven Losh$, and %arr&

'oberts ()

1Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic

Institution, Woods Hole, MA 0!"#Department of Geological $ciences, Cornell %ni&ersity, Ithaca, '( 1")!#

#Coastal $tudies Institute, *ouisiana $tate %ni&ersity, +aton ouge, *A -0)0#

Abstract

Large volumes of gas have vented through a north-south transect of the offshore northern

Gulf of Mexico) *n overvie! of surface and subsurface manifestations of this gas venting is

+resented) This gas movement has caused extensive alteration of reservoired oils to the north of

the transect !hich are estimated to have euilibrated !ith, or been gas !ashed b&, as much as (

volumes of gas for ever& volume of oil) This gas !ashing entrains and carries u+!ard the most

volatile oil com+onents de+ositing them in either shallo!er reservoirs or venting them to the

overl&ing sediments and the !ater column) * significant amount of this gas b&+asses the

reservoirs and vents u+!ard into the overl&ing sediments and !aters) #n s+ite of the significant

amounts of the gas involved, the venting at the seafloor a++ears to occur +rimaril& through highl&

locali.ed faults and fractures) This gas discharge is s+atiall& and tem+orall& heterogeneous,

ma/ing it difficult to estimate the actual h&drocarbon fluxes involved) This u+!ard gas

movement leaves characteristic signatures at the sediment !ater interface including carbonate

+avements in older see+ areas, and chemos&nthetic biological communities, methane h&drates,

and gas see+s in more recent long-term see+ areas) #n some cases !here gas venting is ver&

recent, massive disru+tion of surface and subsurface sediments is observed to be occasionall&

0"orres+onding *uthor Tel 2345 $46-$4167 8ax 2345 93:-$1;9)

./mail address

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accom+anied b& mud volcanoes) >enting can be vigorous enough to +roduce methane gas

bubbles, !hich a++ear to be in


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1. Introduction

The goals of this +a+er are to +resent an overvie! of the d&namic nature of gas

movement along a north-south transect in the Northern Gulf of Mexico (Figure 1)7 demonstrate

the a++arent relationshi+ bet!een subsurface gas movement and surface sediment see+ features,

and 7 sho! ho! these +rocesses might im+act inter+retations of surface see+age as related to the

+resence of underl&ing gas and oil reservoirs) The effects of Gulf of Mexico gas movement on

subsurface oil reservoirs, surface sediments, the !ater column, and the overl&ing atmos+here are

summari.ed) The manifestations of d&namic gas movement described here are not uniue to the

Gulf of Mexico) xam+les of similar see+ features in other geogra+hic areas !orld!ide are

+resented to demonstrate that surface see+age occurs ver& !idel& in some +arts of the ocean

floor, +articularl& along the edges of continents and in ocean margins, even !hen no viable

+roducible +etroleum reservoirs a++ear to be +resent) The !ides+read occurrence of these see+

features, !hich ma& or ma& not be related to subsurface oil and gas de+osits, ma& ex+lain !h&

use of surface see+s has often +roved to be so controversial in oil ex+loration) The relatioshi+

bet!een the surface see+ features and subsurface gas migration through reservoirs along a N-S

transect in the Gulf of Mexico is +resented as one exam+le of the relationshi+ bet!een surface

see+ geolog&, chemistr&, and biolog&, and the d&namics of subsurface gas and oil movement into

and through subsurface +etroleum reservoirs)

2. Summary of effects of gas venting in the orthern !u"f of #e$ico

xtensive research has been carried out in the off shore Green "an&on 2G"1495 area of

the u++er continental slo+e of the northern Gulf of Mexico (Figure 1)near the "onoco Jolliet oil

field) xtensive !or/ has been carried out in this area, including ma++ing seafloor gas, and oil

see+ features (Fu % Aharon& 1''Aharon& Schwarc*& % +oberts& 1'',-roos& Kennicutt&

Fay& #c/ona"d& % Sassen& 1'0 -roos& o$& -ryant& Kennicutt& #ann& % #c/ona"d&

3


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1' -roos& Kennicutt& Fisher& #aco& o"e& hi"dress& et a".& 1', -roos& 3iesenburg&

+oberts& arney& #ac/ona"d& Fisher& !uinasso& et a"& 1''4Kennicutt& -roos& -idigare&

Fay& 3ade& % #c/ona"d& 1'5 Kennicutt& -roos& -idigare& % /enou$& 1'a Kennicutt&

-roos& % /enou$& 1'b 6au""& #artens& anton& eumann& oston& 7u""& et a".& 1''

+oberts& Sassen& arney& % Aharon& 1''4b +oberts& Aharon& arney& % Sassen& 1''4b

+oberts& 3iseman& 8oo9er& % 8um9hrey& 1'''a +oberts& Koh"& #en*ies& % 8um9hrey&

1'''b +oberts& 24417+oberts % arney& 1'',#ac/ona"d& 1'' #i"ov % Sassen& 244a

and 244b)&the stud& of biolog& of chemos&nthetic communities associated !ith the see+s

(-roos et a".,1',,1''4 hi"dress& Fisher& -roos& Kennicutt& -idigare % Anderson&

1' Fisher& hi"dress& ;rem"and& % -idigare& 1', Kennicutt et a".& 1'5 Kennicutt&

-roos& -idigare& % /enou$& 1'a Kennicutt& -roos& % /enou$& 1'b #ac/ona"d %

7oye& 1'', #ac/ona"d& 1'' #ac/ona"d& !uinasso& Sassen& -roos& o& 1''b Sassen&

#ac/ona"d& +e=ue>o& !uinasso& Kennicutt& Sweet& et a".& 1''0a Sassen& o"d& /ro*d& %

+oberts& 1''0b Sassen % +oberts& 1'', Sassen& #ac/ona"d& !uinasso& 7oye& +e=ue>o&

Sweet& et a".& 1'' Sassen& 7oye& Sweet& /eFreitas& #i"ov& % #ac/ona"d& 1'''a Sassen&

Sweet& #i"ov& /eFreitas& Sa"ata& % #c/ade& 1'''b ?hang&


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natural see+s are closel& related geogra+hicall&, !ith +roductive subsurface reservoirs, as sho!n

in Figure 12ada+ted from Sassen et a".& 1''b5) * summar& of surface and subsurface

+henomena associated !ith the northern Gulf of Mexico gas see+s is sho!n schematicall& in

Figure 2) These venting features +roduce a substantial oil and gas flux into the overl&ing !ater

column as sho!n b& huge oil slic/sover non oil +roductive areas described b& #ac/ona"d&

!uinasso& Ac"eson& Amos& /ucworth& Sassen& % -roos (1'')& #ac/ona"d& +ei""y& -est&

enataramaiah& Sassen& Amos& et. a". (1'')& #ac/ona"d&


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surface sediment manifestations of these see+s !ere described and ma++ed b& various grou+s as

described above) The organisms found in these areas are reminiscent of the +rolific

chemos&nthetic biological communities that are ubiuitous in h&drothermal vent areas (8ess"er

% Kahar"& 1''5).

#n the Gulf of Mexico, the +rimar& food source for these see+ communities a++ears to be

a com+lex chemos&nthetic communit& of microorganisms utili.ing a cou+led +rocess of

h&drocarbon 2+rimaril& methane5 oxidation and sul+hate reduction 2termed anaerobic oxidation

of methane, or *@M5, similar to that !hich has been described at a number of other oceanic

methane h&drate and see+ sites 2e)g), 8inrichs& 8ayes& Sy"va& -rewer& % /e


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+oberts % arney (1'',)describe three general +atterns of see+age 15 long-term

see+age that +roduces giant carbonate mounds 2commonl& tens of metres high57 $5 ongoing

intermediate see+age rates that su++ort extensive biological communities, carbonate crusts, and

methane h&drates7 and (5 ver& recent oil and gas e


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gas h&drates found in the area (Sassen et a".& 1'''a& 2441a& 2441b Sassen& 2441)) Thermogenic

gas is the most viable +rimar& chemos&nthetic food source for the biological communit& that

overlies the Bush %ill gas h&drate mound (Sassen et a".& 1''a& 1''b& 1'' Sassen %

#ac/ona"d& 1'',


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. Summary of effects of ocean bottom gas venting wor"dwide

The surface and subsurface gas venting features described above are not uniue to the

Gulf of Mexico) The +henomena associated !ith these seafloor gas see+ages are often not subtle

and have no! been observed in a number of areas of the !orld, as described in recent revie!s

(7udd& 1'',7 8ov"and % 7udd& 1' 8ov"and % 7udd& 1''27udd et a".& 2442)) Some of

these areas, indicated on the ma+ in Figure 5, include the North Sea (7ensen& Aagaard& -ure&

/ando& 7Ergensen& Kui>9ers& et a".& 1''27udd& 1'', 8ov"and % #ortensen& 1''' -oe&

8ov"and& Instanes& +ise& % asshus& 2444), the Berants Sea(


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#usgrave& Ashi& -aranov& -rown& et a".,1''5)) %o!ever, to the north, more than 1)3 tons of

gas h&drates !ere recentl& accidentall& dredged from the seafloor of the "anadian "ascadian

Margin b& some ver& sur+rised fishermen (Figure )) These h&drates !ere covered !ith oil,

leading to the conclusion that the& are associated !ith thermogenic +etroleum and gas de+osits)

>enting of this nature often occurs at continental margins and other locations !here

circulation bet!een gas-containing and o+en ocean !aters are not as restricted as is the case for

the Gulf of Mexico (Figure 5)) "om+arison of the Gulf of Mexico see+s !ith see+s !orld!ide

suggests that the latter are currentl& under-a++reciated b& the scientific communit&, even though

the& ma& be having significant effects on a number of im+ortant geological, oceanogra+hic, and

atmos+heric +rocesses (7udd& 1'', 7udd& 8ov"and& /ivitrov& !arcia& % 7ues& 2442))

See+s and their fossil manifestations H I+oc/mar/s in the seafloor - also a++ear to be

ubiuitous on man& +arts of the ocean floor, +articularl& in river deltas, !hich have ra+id

sedimentation rates, and on continental margins associated !ith subduction .ones (8ov"and %

7udd& 1'7 8ov"and et al.& 2442 7udd et al.& 2442 "enne""& et al.& 2444)) Where !ater

de+ths are sufficient to +rovide high +ressures and lo! tem+eratures, the u+!ard-see+ing gas

commonl& +roduces gas h&drate de+osits at or


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#t has been +ro+osed that gas see+age ma& contribute to slo+e sediment destabili.ation

leading to the huge under!ater mudslides commonl& observed on continental slo+es 2e)g)

Ducho"e& -ryan& % Hwing& 1',, Dhiery& -aer& % #onnin& 1''7 "enne"" et a".& 2444

+oberts& 2441). * dramatic recent exam+le has been documented on the eastern continental slo+e

off North "arolina (Figure 117 /risco""& 3eisse"& % !off& 2444)!here methane rich +lumes and

h&drates have also been documented (6au""& Css"er& -orowsi& % S9iess,1''5)) #t has been

+ostulated that the slide 2Figure 115 is large enough to cause a tidal !ave if it ha++ened toda&)

Note the small dim+les 2a and b5 at the to+ of the slo+e in Figure 11thesea++ear to be

+oc/mar/s, or de+ressions, !hich are commonl& caused b& fluid discharge 2gas or liuid5 to the

seafloor, similarl& to those documented in 8ov"and % 7udd (1'). Scri++s and Woods %ole

grou+s have recentl& ma++ed methane see+age associated !ith one of the +oc/mar/s in Figure

11(/risco"" and ami""i& un9ub"ished resu"ts)) More !or/ is reuired to find out !hether or

not sufficient gas is +resent, and could be vented, to cause a slo+e failure at this location) *n

alternative mechanism of slo+e failure has been +ro+osed b& /ugan % F"emings (2444 2442),

!hich involves sediment com+action, over+ressuring, and de!atering +ossibl& enhanced b&

offshore ground !ater movement)

0. !u"f of #e$ico B Subsurface effects of gas movement

The Woods %ole research on the Gulf of Mexico oil and gas see+s began !ith the finding

of ra+id 2less than 1 &ear5 changes in oil com+ositions in #(( oil reservoirs, to!ard the

southern end of the N-S transect in Figure 1these changes do not a++ear to be attributable to

+roduction effects (Schumacher& 1'' 3he"an& 1'', 3he"an& Kennicutt& -roos&

Schumacher& % Hg"inton& 1''0 3he"an& et a".& 2441)) 8urther investigation sho!ed that the

oils in this stac/ed reservoir seuence !ere being altered b& u+!ard migration of large volumes

of gas in a +rocess defined as Agas !ashingA (#eu"broe& ath"es& % 3he"an& 1'')envisioned

as multi+le volumes of gas streaming into and euilibrating !ith oil in reservoirs (Figure 12)&

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follo!ed b& the gas +hase continuing to stream u+!ard) The resulting fractionations of n-al/anes

observed in these Agas-!ashedA oils have been successfull& modeled using multi+le seuential

volumes of gas coming from dee+er intervals !hich euilibrate !ith the oil, and then continue an

u+!ard +ath into shallo!er reservoirs (Figure 12)) This +rocess, !hich !as first studied in detail

for the #(( oils (#eu"broe& et a".,1''), causes the lo!est molecular !eight h&drocarbons to

be s!e+t out of the oil +referentiall& and enriched in the moving gas stream so that shallo!er

reservoirs become enriched in +rogressivel& lighter h&drocarbons (Figure 12


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south, Figure 105) There is no evidence that the G"149 oils furthest to the south have

ex+erienced an& a++reciable gas !ashing)

The relative timing of gas !ashing and the associated gas movement along the N-S

transect inFigure 0can be estimated b& also considering other +rocesses !hich might be

res+onsible for these +rogressive changes in com+osition, including biodegradation, source

changes, and maturit&) Throughout the transect, less mature oil is mixed !ith more mature gas, as

described +reviousl& for #(( (3he"an& et a".& 1''0 3he"an& Hg"inton& +e=ue>o& %

Kennicutt& 1''5)) 'ecent modeling, combined !ith the organic geochemical data, sho!s that oil

generation +robabl& too/ +lace in the Miocene from roc/s currentl& buried directl& beneath their

+resent da& Cleistocene reservoirs (oe"ho& 1'', Hrendi& 2441 ath"es et al.& un9ub"ished

data)) Therefore, oil generation +robabl& occurred considerabl& before the time of formation of

the +resent da& Cleistocene reservoirs and !as initiall& tra++ed beneath salt sheets, as sho!n

schematicall& in Figure 15)

The influence of source changes is considered to be minimal) %o+ane and sterane

biomar/ers are remar/abl& similar for the shallo!er shelf oils to the north 2SM#65 and the dee+er

!ater oils at the south 2G"149,5 even though there a++ears to be an enhanced contribution from

&ounger ocene oils to the north and older "retaceous and Jurrassic oils to the south) Man& of the

oils to the north of the transect a++ear to be mixed !ith Tertiar& sourced oil, as sho!n b& slightl&

higher amounts of diben.othio+heneF+henanthrene !hich increases in oils to the south of the

transect (Figure 1a). #ncreases in this ratio are indicative of an increased source in+ut from

higher sul+hur more marine /erogens (8ughes& 8o"ba& % /*ou& 1''5)) #n addition, the

+ro+ortion of oleanane, diagnostic of in+ut from source roc/s containing higher +lant in+ut,

simultaneousl& increases to the north 2not sho!n5 as !ould be ex+ected if sourced from the

shallo!er terrigenous Tertiar& roc/s in this area, but not from the older and more marine Jurassic

and "retaceous roc/s) * similar trend results !hen the ratio of oleanane to " ( ho+ane is +lotted

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2not sho!n5) (%o+ane is commonl& used as a mar/er for in+ut of marine organic matter

(6eters % #o"dowan& 1''))

The differences in most biomar/ers are uantitativel& minor, even though the& are useful

for distinguishing at least t!o different oil families) #'G"MS anal&ses of individual ": to "1

com+onents (Figure 1b)also reveal t!o end members of a series) SM#6 oils are statisticall&

distinct from G"149 oils (Figure 1b)) This similarit& in source of a ma


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at higher +ressures (7annasch % Day"or& 1'0 +ueter& +abus& 3i"es& Aecersberg& +ainey&

7annasch& et a".& 1''0 Stetter& 8uber& -"och"& Kurr& Hden& F"eder& et a".& 1'' !ibson&

1'0 Singer % Finnerty& 1'0)) *naerobic sul+hate reducing microbes of a moderatel&

thermo+hilic nature 2;"5 have been isolated) These consortia utili.e n-al/anes from ";to "1;

as substrates (+ueter et a".& 1''0)!ith the best gro!th occurring in the "4-"1$range) This is the

carbon range that is commonl& the most de+leted in +artiall& biodegraded Gulf "oast oils

(3he"an et a".& 2441)) * recent revie! of biological activit& in dee+ subsurface +etroleum

reservoirs +ro+oses that the rate of su++l& of nutrients is a critical control on the rate of +etroleum

biodegradation in these dee+ reservoirs 28ead& 7ones& %


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consistent !ith the maturit& data for the transect !hich sho! an overall gradual change from

more mature to the north 2SM#6, MC#-1 1)15 to less mature in the south 2G"149, MC#-1 )6,

Figure 15) Su+erim+osed on this general trend are Ahot s+otsA of higher maturit& oil !hich are

+ossibl& inter+reted as indicating .ones of higher heating !here /erogen and oils !ere, until ver&

recentl&, tra++ed beneath salt in dee+er sediments)

5. +e"ation of surface and subsurface gas migration in the !u"f of #e$ico

The most general and sur+rising conclusion of our research on oils and gases in the Gulf

of Mexico N-S transect has been the ra+id and d&namic nature of the !hole oil-gas generation-

migration s&stem in this area) This +ervasive gas movement at various times and various +laces,

both over geologic time and continuing u+ to the +resent time, directl& affects the st&le of see+age

overl&ing various +arts of the transect) The extensive and older gas migration s&stem to the north

has given rise to the isoto+icall& light carbonate +avements and mounds on the seafloor across

much of the continental shelf) The sediments overl&ing #(( at the shelf edge also contain

carbonate +avements and a++arent signs of active chemos&nthetic communities fed b& underl&ing

gas) *t the southern end of the transect, G"149 reservoirs do not &et sho! evidence of alteration

of oils in reservoirs, but do sho! strong evidence of active +resent da& gas migration through

surface sediments) This gives rise to gas bubble venting though fractures, surface sediment gas

h&drates, chemos&nthetic biological communities, and mud craters and volcanoes, as discussed

+reviousl&)

Similar observations have been made at a number of other seafloor h&drate de+osits,

including some in much dee+er !ater, such as the "ascadian Margin (Suess& Dorres& -ohrmann&

o""ier& +icert& !o"dfinger& et a".& 2441)) These observations suggest a ver& d&namic gas flo!

s&stem in some cases !here gas h&drates are onl& the e+himeral manifestation of a much larger

gas flo! s&stem, as +reviousl& +ro+osed b& /icens (1''' 2441a 2441b). *t the Bush %ill

G"149 site,hen % ath"es (244)com+ared the si.e of +resent-da& h&drate de+osits !ith the

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calculated rate of gas deliver& using basin and fluid flo! modeling) #t !as concluded that gas is

being activel& delivered to the h&drate at the +resent time and that 6O of this gas is being

activel& vented to the ocean, !hile onl& 1O is tra++ed in the h&drate) ata of Sassen et a".

(2441a) !ere used to sho! that isoto+ic +ro+erties of the u+!ard streaming gas and of the gas

h&drate are identical, ma/ing se+arate gas sources for the h&drate and venting methane unli/el&)

. an surface see9s be used to e$9"ore for subsurface oi" 6ers9ective from a mass

ba"ance 9oint of view.

The results described above suggest a +otentiall& substantial difficult& in using surface

see+s to ex+lore for subsurface oil7 a large ubiuitous Abac/groundA of gas see+age moving

continuousl& through the subsurface ma&, in some areas, ma/e utili.ation of see+s in ex+loration

ver& confusing) #n the absence of ancillar& geochemical, geological, and geo+h&sical data, the

+resence of this bac/ground gas ma/es difficult the determination of !hen and ho! a surface gas

see+ is related to an economic subsurface +etroleum accumulation) The magnitude of the +roblem

can be a++reciated b& considering that, !orld!ide, less than $O of generated gas and oil is ever

found in a +roducible reservoir) @f the remainder, about half is vented into the ocean, !hile the

other half remains in the subsurface (3he"an& et a".& 2441& estimated using data from 8unt&

1'')) * significant +ortion of this Anon-reservoirA gas ma& be available for the +rocesses

described here that reuire a continuous gas stream, including gas !ashing of oils, gas venting

through surface sediments, gas h&drate formation, and the feeding of chemos&nthetic biological

communities)

Where is all this gas coming fromP We suggest that ubiuitous thermogenic and biogenic

methane generation +rocesses, !hich occur in most organic-carbon containing sediments

!orld!ide, are res+onsible) Thermogenic methane generation is ubiuitous in sediments having

as little as )3O total organic carbon and !hich are ex+osed to tem+eratures of 4" and higher

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(8unt& 1''). Similarl&, methanogenesis 2or anaerobic biogenic methane generation5 is almost

ubiuitous in sediments having as little as )(O total organic carbon and has been observed to

sub-bottom de+ths of at least 4m sub-bottom (6ares& ragg& -a"e& !et"eiff& !oodman&

+oche""e& et a".& 1''0)) T!o im+ortant and abundant starting materials for both +rocesses,

/erogen - com+rising, the bul/ of the T@" +ool of most sediments- and carbonate carbon,

re+resent t!o of the largest carbon +ools on earth 2Kvenvo"den& 1''5) Therefore, it !ould not

be sur+rising if some +ortion this Abac/groundA gas generation and migration is confusing our

inter+retations of surface see+ data)

#n d&namic gas migration s&stems such as that described here for the Gulf of Mexico

transect, an activel& charging economic reservoir could be confused for an old lea/& non-

economic one) The s+ecific seafloor manifestations of see+age described above can hel+ in

distinguishing these t!o +ossibilities) 8urthermore, if the gas streams !hich carr& underl&ing oil

com+onents u+!ard are !ides+read, then it ma& be +ossible to utili.e the com+lex see+

h&drocarbon signatures in much smarter !a&s than has +reviousl& been +ossible)

The research +resented here suggests a general !a& that molecular h&drocarbon see+ data

could be used to gain a more uantitative +icture of gas flo! through the subsurface using

+rocedures similar to those described here for elucidating the degree of subsurface gas !ashing

2Figures 1 and 105)

#n conclusion, surface see+s are not a Amagic bulletA for +etroleum ex+loration) Their full

+otential can onl& be reali.ed if individual com+ounds in see+s can be se+arated and uantitated,

and their signatures distinguished from those of sediments surrounding the see+s) #n addition,

diagnostic molecular see+ information related to subsurface accumulations must be inter+reted in

the broader context of all available geochemical, geological, geo+h&sical, oceanogra+hic, and

atmos+heric data available for a +articular area) The first ste+ might be to use see+ data together

!ith initial geo+h&sical and !ell data to determine !hether or not a +articular A+etroleum s&stemA

is relativel& closed, as is currentl& generall& assumed, or if it is more of a moving stream similar

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to that envisioned for the Gulf of Mexico transect gases in Figures 2and 15) This distinction is

im+ortant in deciding !hether a see+ re+resents an activel& charging economic reservoir, an old

lea/& non-+roductive reservoir, or some other state l&ing bet!een these t!o extremes)

,. onc"usions

vidence for the d&namic nature of gas movement in both surface and subsurface

sediments through a N-S transect in the northern Gulf of Mexico has been +resented) Some of the

effects discussed include

Q gas h&drates

Q gas bubble streams issuing through fractures and faults in the seafloor, even in dee+ !ater

Q +oc/mar/s and craters in the seafloor

Q mud volcanoes

Q carbonate +avements

Q large oil slic/s that cover large areas of the ocean having no oil +roduction

Q +rolific chemos&nthetic communities of organisms su++orted b& h&drocarbons and

sul+hur as the +rimar& food sources

Q evidence of massive disru+tion of subsurface sediments

Q alteration of some subsurface oils and gases on short time scales

Q significant alteration of oils in reservoirs b& u+!ard gas movement and gas !ashing

These +rocesses are not confined to the Gulf of Mexico7 exam+les are +resented to sho!

that similar +henomena occur in man& areas !orld!ide !ith ne! ocean bottom see+ areas

continuing to be discovered) These +rocesses ma& be so !ides+read that the& lead to confusion

in the utili.ation of surface see+s to ex+lore for subsurface economic +etroleum accumulations) *

revie! of these +rocesses as the& occur in the Gulf of Mexico is +resented, along !ith a

discussion of the close inter-relationshi+ of see+ing gas and its associated biota, gas flo! through

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and around +etroleum reservoirs, gas h&drates, and observations of ocean-floor see+ associated

biota)

The general relationshi+ bet!een the nature of the surface see+ features and the relative

amount and timing of gas movement through subsurface oils is described for a N-S transect in the

northern Gulf of Mexico) Large volumes of gas can be involved7 as much as ( times the oil

volume !as estimated for some reservoirs in the transect) The degree of gas !ashing a++ears to

be reflected in the general nature of gas see+ features in surface sediments overl&ing these

reservoirs) The reservoirs to the north !hich have ex+erienced the most gas !ashing are overlain

b& carbonate +avements characteristic of older AfossilA see+s, !hile com+lex chemos&nthetic

communities, surface gas see+s, and active gas bubble discharge areas increase graduall& to the

south, reaching a +ea/ over the southern-most Green "an&on reservoirs !hich currentl& sho!

little or no evidence of alteration of reservoir oils b& gas !ashing) #t is +ro+osed that these

features of +resent da& gas see+age overl&ing Green "an&on reservoirs are diagnostic of a much

earlier stage of gas generation and movement, +ossibl& diagnostic of active +resent da& reservoir

charging)

#t is suggested that the relationshi+ bet!een surface see+ oils and subsurface +etroleum

+lumbing !ithin this N-S transect in the northern Gulf of Mexico, far from being an anomal&, can

serve as a natural laborator& for other see+-reservoir s&stems !orld!ide) 8uture !or/ should

focus on utili.ing the uantitative geochemical data from s+ecific organic com+ounds in the see+

- along !ith the geolog&, geo+h&sics, and biolog& - in order to gain more information about the

nature of an& of the underl&ing reservoirs !ith res+ect to oil ualit&, timing of reservoir filling,

and +robable degree of alteration b& gas !ashing, !ater !ashing, and biodegradation)

21


22/42

Figures

8igure 1 Ma+ of oil and gas see+sFchemos&nthetic communities and recent +etroleum

discoveries 2ada+ted from Sassen et a".& 1''a and 1''b). The location of N-S

!ell transect on u++er slo+e of northern Gulf of Mexico is indicated b& the heav&

blac/ line)

8igure $ Summar& of all gas see+ related +rocesses observed in the vicinit& of Green

"an&on area in the northern Gulf of Mexico, at the south end of the transect sho!n

in 8igure 1)The +rocesses sho!n include thermogenic oil and dee+er gas

generation 2to the left5 and biogenic methane generation 2to the right5) ither

source of gas can then migrate u+!ard either ra+idl& through faults and fractures or

more slo!l& b& diffusion through sediments into overl&ing oil and gas reservoirs)

#n either case, most of the gas b&+asses the reservoirs and migrates further u+!ard

to the sediment !ater interface !here it can form gas 2methane5 h&drate de+osits

2sho!n in !hite5 or can be vented into the overl&ing !ater column) #f methane

concentrations do not reach saturation, the gas in the dissolved +hase is largel&

biodegraded in the !ater column) Where sufficient methane is +resent, gas bubbles

form and, if the& survive to !ithin 1m of the surface, can be vented as methane

into the atmos+here) #n some cases, the bubbles are coated !ith oil 2see


23/42

thic/ allocthonous Jurassic salt) The straight lines are faults, and the circles and

boxes are cross-line inter+retations of hori.ons and faults 2from 8unt& 1''5

8igure 9 Generali.ed subsurface +rofile of Gulf "oast transect !here Miocene and &ounger

sediments overlie salt 2bro!n5 and dee+er, older Iun/no!n formations)

8igure 3 Ma+ of occurrence of some of gas see+s described to date !orld!ide) Ne! areas of

see+age continue to be discovered)

8igure ; Mixture of methane h&drates and +etroleum accidentall& dredged from the sea-

bottom in the "anadian "ascadia margin.

8igure : Gas and !ater continuousl& rise u+ from one of numerous mud volcanoes in

*.erbai


24/42

8igure 11 Massive slide on continental slo+e, offshore North "arolina) Note +oc/mar/s on

u++er shelf edge 2a and b5 !hich ma& be indicative of gas see+age at the to+ of the

slo+e 2from /risco"" et a".& 24445) *lso indicated is a slideFslum+ 2c5, +ostulated to

have been triggered b& +ast gas flo!) #nset sho!s location of this area as


25/42

the north !ith anomalous .ones of higher maturit& these are Khot s+otsK occurring

at a number of # !ells in the center of the transect) These hot s+ots are +ostulated

to re+resent u+!ard in


26/42

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*haron, C), Sch!arc., %)C), D 'oberts, %)%) 2166:5) 'adiometric dating of submarine

h&drocarbon see+s in the Gulf of Mexico GS* Bulletin, 16, 3;4-3:6)

Boe, ', %ovland, M), #nstanes, *), 'ise, L) D >asshus, S) 2$5) Submarine slide scars and mass

movements in Rarmsundet and S/udenesfetter, ')) 2164:5 ee+-sea h&drocarbon see+ communities vidence for

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Buffett, B)*), 2$5) "lathrate h&drates)Annual e&ie of .arth and lanet $ciences, $4, 9::-

3:)

"arson, B), Westbroo/, G)R), Musgrave, ')J), *shi, J), Baranov, B), Bro!n, R)M), "amerlenghi,

*), "aulet, J-C), "hamov, N)C), "lennell, M), "ragg, B)*), ietrich, C), 8oucher, J)-C),

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27/42

%ousen, B), %ovland, M), Jarrard), ')), Rastner, M), Ro+f, *), MacRa&, M)), Moore, "),

Moran, R), Car/es, J), Sam+le, J), Sato, T), Screaton, )J), Tobin, %)J), Whiticar, M)J, D

ellers, S)) 216635) @cean rilling Crogram, Scientific 'esults, l)19;, 2+) 9::5)

"harlou, J)-L), onval, J)-C), itter, T), 'o&, N), Jean-Ba+tiste, C), 8oucher, J)-C), D Woodside, J)

2$(5) vidence of methane venting and geochemistr& of brines on mud volcanoes of the

eastern Mediterranean Sea)Deep/$ea esearch I, 3, 691-634)

"hen, )8), D "athles, ###, L) 2$(5) * /inetic model for the +attern and amounts of h&drate

+reci+itated from a gas stream a++lication to the Bush %ill vent site, Green "an&on Bloc/

143, Gulf of Mexico2ournal of Geophysical esearch, 14, $34)

"hildress, J)J), 8isher, ")'), Broo/s, J)M), Rennicutt ##, M)"), Bidigare, '), D *nderson, *))

2164;5 Methanotro+hic marine molluscan 2Bivalvia, M&tilidae5 s&mbiosis mussels fueled

b& gas) $cience, $((, 1(;-1(4)

"lennell, M)B), Judd, *), D %ovland, M) 2$5) Movement and accumulation of methane in

marine sediments7 relation to gas h&drate s&stems) #nM3D3 Ma4, Coastal $ystems and

Continental Margins) 2+) 13-1$$5) ordrecht, Rlu!er)

"oelho, )8) da Silva, 166:, Three imensional *nal&sis of the Tem+erature in Bloc/ ((,

South ugene #sland, Gulf of Mexico Ch)) issertation, "ornell ?niversit&, #thaca, N,

$6$ +)

"oo+er, *)R), D %art, C)) 2$(5) %igh-resolution seismic-reflection investigation of the

northern Gulf of Mexico gas-h&drate stabilit& .one)Marine and etroleum Geology,

+ersonal communication)

"uriale, J)*), D Bromle&, B)W), 2166;a5) Migration of +etroleum into >ermilion 19 field, Gulf

"oast, ?) S) *) - molecular evidence) Organic Geochemistry, $9, 3;(-3:6)

"uriale, J)*), D Bromle&, B)W) 2166;b5) Migration induced com+ositional changes in oils and

condensates of a single field) Organic Geochemistry, $9, 16:-111()

27


28/42

eville, ), Battani, *), Griboulard, '), Guerlais, S), Lallemant, S), Mascle, Crin.hofer, *), D

Schmit., J) 2$(5) Crocesses of mud volcanism in the Barbadoes-Trinidad com+ressional

s&stem ne! structural, thermal and geochemical data) #nAmerican Association of

etroleum Geologists, A5stracts of Meeting, AAG Annual Con&ention, $alt *a6e City,

%tah, May 11/1", 7) Tulsa *merican *ssociation of Geologists)

ic/ens, G)') 216665 The blast in the +ast)'ature) 91, :3$-:33)

ic/ens, G) 2$1a5) @n the fate of +ast gas What ha++ens to methane released from a

bacteriall& mediated gas h&drate ca+acitorP Geochemistry, Geophysics, Geosystems, $)

ic/ens, G)'), 2$1b5) Modeling the global carbon c&cle !ith a gas h&drate ca+acitor

Significance for the latest Caleocene thermal maximum) Natural Gas %&drates @ccurrence,

istribution, and etection)American Geophysical %nion3 Geophysical Monograph 1, 2+)

$95)

riscoll, N), Weissel, J)R), D Goff, J)*) 2$5) Cotential for large-scale submarine slo+e failure

and tsunami generation along the ?)S) mid-*tlantic coast) Geology) $4, 9:-91)

ugan, B), D 8lemings, C)B) 2$5) @ver+ressure and fluid flo! in the Ne! Jerse& continental

slo+e7 im+lications for slo+e failure and cold see+s) $cience, $46, $44-$61)

ugan, B), and 8lemings, C)B) 2$$5) 8luid flo! and stabilit& of the ?S continental slo+e

offshore Ne! Jerse& from the Cleistocene to the +resent) Geofluids, $, 1(:-19;)

.ou L)#)C), D %ughes, W)B) 2166(5) Geochemistr& of oils and condensates, R 8ield, offshore

Tai!an a case stud& in migration fractionation) Organic Geochemistry, $, 9(:-9;$)

rendi, *) 2$15) "om+uter Simulation of Geological Crocesses, Ch) issertation, "ornell

?niversit&, #thaca, N) 2+) $$:5)

8ader, G)B)J), 1661, Gas-related sedimentar& features from the eastern "anadian continental

shelf "ontinental Shelf 'esearch, v) 11, +) 11$(-113()

28


29/42

8isher, ")'), J)J) "hildress, ')S) @remland and ')') Bidigare, 164:, The im+ortance of methane

and thiosul+hate in the metabolism of the bacterial s&mbionts of t!o dee+-sea mussels

Marine Biolog&, v) 6;, +) 36-:1)

8u, B), D *haron, C) 216645) Sources of h&drocarbon-rich fluids advecting on the seafloor in the

northern Gulf of Mexico) 8ransactions Gulf Coast Association of Geological $ocieties, 94,

:(-4$)

Gibson, )T) 216495 Microbial egradation of @rganic "om+ounds) Ne! or/ Marcel e//er,

#nc), +) 3(3)

Guli&ev, #) 2$(5 South "as+ian Basin - excitement and movement of sedimentar& masses

mechanism and geologic conseuences) #nAAG Annual Con&ention, May 11/1", 00#,

$alt *a6e3City, 2+) $(-$45)

%ead, #)M), Jones, )M), D Larter, S)') 2$(5) Biological activit& in the dee+ subsurface and the

origin of heav& oil)'ature, 9$;2$5, (99-()

%essler, ')'), D Raharl, >)*) 216635) The dee+-sea h&drothermal vent communit& an overvie!)

#n $3.3 Humphris, 3A3 9ieren5erg, *3$3 Mullineau4, and 3.3 8homson, $eafloor

hydrothermal systems: Geophysical Monograph 71, Washington, DC, American

Geophysical %nion) + :$-49)

%inrichs, R)-?), %a&es, J)M), S&lva, S)C), Bre!er, C)G), D eLong, )8) 216665) Methane-

consuming archaebacteria in marine sediments)'ature, (64, 4$-43)

%inrichs, R)-?), Summons, ')), @r+han, >), S&lva, S)C), D %a&es, J)M) 2$5) Molecular and

isoto+ic anal&sis of anaerobic methane-oxidi.ing communities in marine sediments)

Organic Geochemistry, (1, 1;43-1:1)

%inrichs, R)-?), D Boetius, *) 2$$5) The anaerobic oxidation of methane Ne! insights in

microbial ecolog& and biogeochemistr&) #n Ocean Margin $ystems2ed) G) Wefer et al)5)

2++) 93:-9::5) Berlin-%eidelberg S+ringer >erlag)

29


30/42

%olba, *)G), .ou, L)#)C), %ic/e&, J)J), 8ran/s, S)G), Ma&, S)J), D Lenne&, T) 2166;5) 'eservoir

geochemistr& of South Cass ;1 8ield, Gulf of Mexico com+ositional hetrogeneities

reflecting filling histor& and biodegradation) Organic Geochemistry, $9, 11:6-1164)

%ovland, M), D Judd, *)G) 216445 Seabed Coc/mar/s and See+ages) #nImpact on Geology,

+iology and the Marine .n&ironment) London Graham and Trotman) +) $6()

%ovland, M), D Judd, *)G) 2166$5) The global +roduction of methane from shallo! submarine

sources) Continental $helf esearch, 1$, 1$(1-1$(4)

%ovland, M), "ro/er, C)8), D Martin, C)8) 216695) 8ault-associated seabed mounds 2carbonate

/nollsP5 off !estern #reland and north-!est *ustralia)Marine and etroleum Geology, 11,

$($-$9);

%ovland, M), D xThomsen, C)8) 2166:5) "old-!ater corals7 are the& h&drocarbon see+ relatedP

Marine Geology, 1(:21-$5, 136-1;9)

%ovland, M), %ill, *), D Sto/es, *) 2166:5) The structure and geomor+holog& of the ashgil mud

volcano, *.erbai


31/42

%ovland, M), Gardner, J)>), Judd, *)G) 2$$5) The significance of +oc/mar/s to understanding

fluid flo! +rocesses and geoha.ards) Geofluids, $, 1$:-1(;)

%ughes, W)B), %olba, *)G), D .ou, L)C) 216635) The ratios of diben.othio+hene to

+henanthrene and +ristane to +h&tane as indicators of de+ositional environment and

litholog& of +etroleum source roc/s) Geochimica et Cosmochimica Acta, 36, (341-(364)

%unt, J)M) 2166;5) Cetroleum Geochemistr& and Geolog&) $ndedition) Ne! or/ 8reeman) +)

:9()

Jannasch, %)W), D Ta&lor, ")) 216495) ee+-sea Microbiolog&)Annual e&ie of Micro5iology,

(4, 94:-319)

Jensen, C), *agaard, #), Bur/e, Jr), ')*), ando, C)'), JUrgensen, N)@), Rui) 2$$5) The geological

methane budget at continental margins and its influence on climate change) Geofluids, $,

16-1$;)

Relle&, J)T), ic/son, S)M), Bel/na+, )8), Barnhardt, W)*), D %enderson, M) 216695) Giant sea-

bed +oc/mar/s7 evidence for gas esca+e from Belfast Ba&, Maine) Geology, $$, 36-;$)

Rennicutt, M)"), ##, Broo/s, J)M), Bidigare, ')'), 8a&, ')'), Wade, T)L), D Mconald,

T)J) 216435) >ent-t&+e taxa in a h&drocarbon see+ region on the Louisiana slo+e)

'ature, (1:, (31-(3()

31


32/42

Rennicutt, ##, M)"), Broo/s, J)M), Bidigare ')'), D enoux, G)J) 21644a5) Gulf of Mexico

h&drocarbon see+ communities, #) 'egional distribution of h&drocarbon see+age and

associated fauna)Deep/$ea esearch, (3, 1;(6-1;31)

Rennicutt, ##, M)"), Broo/s, J)M), D enoux, G)J) 21644b5 Lea/age of dee+, reservoired

+etroleum to the near surface of the Gulf of Mexico continental slo+e)Marine Chemistry,

$9, (6-36)

Rohl, B) D 'oberts, %)%) 216695) 8ossil foraminifera from four active mud volcanoes in the Gulf

of Mexico) Geo/Marine *etters, 19, 1$;-1(9)

Rulm, L)), Suess, ), Moore, J)"), "arson, B), Le!is, B)T), 'itger, S)), Rad/o, )"),

Thornsburg, T)M), mble&, ')W), 'ugh, W)), Massoth, G)J), Langseth, M)G), "ochrane,

G)'), D Scamman, ')#) 2164;5) @regon subduction .one venting, fauna and carbonates)

$cience, $(1, 3;1-3;;)

Rvenvolden, R)*) 2166(5) Gas %&drates-Geological +ers+ective and global change)e&ies of

Geophysics, (1, 1:(-14:)

Rvenvolden, R)*), D Lorenson, T) ) 2$15) *ttention turns to naturall& occurring methane

see+age).O$, 4$, 93:

Rvenvolden, R)*), D 'ogers, B)W) 2this volume5) GaiaKs breath-global methane exhalations)

Lammers, S), Suess, ), D %ovland, M) 216635) * large methane +lume east of Bear #sland

2Barents Sea57 im+lications for the marine methane c&cle)Geologische undschau, 49, 36-

;;)1

Lanoil, B)), Sassen, '), La uc, M)T), S!eet, S)T), D Nealson, R)%) 2$15) Bacteria and

*rchaea +h&sicall& associated !ith Gulf of Mexico gas h&drates)Applied and

.n&ironmental Micro5iology, ;:, 319(-313()

Leifer, #), D Boles, J) 2this volume5) Measurement of marine h&drocarbon see+ flo! through

fractured roc/ and unconsolidated sediment)

32


33/42

LUseth, %), Wensaas, L), *rntsen, B), %an/en, N), "hristo+he, B), D Gaue, R) 2$(5) 1 Meter

Long Gas Blo!-@ut Ci+es)AAG Annual Con&ention, May 11/1", 00#, $alt *a6e3City,

%tah)

Losh, S), "athles, L), D Meulbroe/, C) 2$$a5) Gas !ashing of oil along a regional transect,

offshore Louisiana) Organic Geochemostry, ((, ;33-;;()

Losh, S), Walter, L), Meulbroe/, C), Martini, *), "athles, L), D Whelan, J) 2$$b5) 'eservoir

fluids and their migration into the South ugene #sland bloc/ (( reservoirs, offshore,

Louisiana *merican *ssociation of Cetroleum Geologists Bulletin,v) 4;, +) 19;(-1944)

Luth, "), Luth, ?), Gebru/, *)>), D Thiel, J) 216665) Methane gas see+s along the oxicFanoxic

gradient in the Blac/ Sea Manifestations, biogenic sediment com+ounds and +reliminar&

results on benthic ecolog&)Marine .cology, $, $$1-$96)

Maconald, #)'), Guinasso, N)L), 'eill&, J)8), Broo/s, J)M), allender, W)'), D Gabrielle, S)")

2166a5) Gulf of Mexico h&drocarbon see+ communities) >#) Catterns of communit&

structure and habitat) Geo/Marine *etters, 1, $99-$3$)

Maconald, #)'), "allender, W)'), Bur/e, Jr), ')*), Mconald, S)J), D "arne&, ')S) 2166b5

8ine-Scale distribution of methanotro+hic mussels at a Louisiana cold see+ Crogress in

@ceanogra+h&, v) $9, +) 13-$9)

Maconald, #)'), Guinasso, Jr), N)L), *c/leson, S)G), *mos, J)8), uc/!orth, '), Sassen, '), D

Broo/s, J)M) 2166(5) Natural oil slic/s in the Gulf of Mexico visible from s+ace) 2ournal of

Geophysical esearch, 64, 1;(31-1;(;9)

Maconald, #)'), Guinasso, Jr), N)L), Sassen, '), Broo/s, J)M), Lee, L), D Scott, R)T) 216695)

Gas h&drate that breaches the sea floor on the continental slo+e of the Gulf of Mexico)

Geology, $$, ;66-:$)

Maconald, #)'), 'eill& Jr), J)8), Best, S)), >en/ataramaiah, '), Sassen, '), *mos, J), D

Guinasso, Jr), N)L) 2166;5) * remote-sensing inventor& of +erennial oil see+s and

chemos&thetic communities in the Northern Gulf of Mexico) #nD3$chumacher and M3A3

33


34/42

A5rams, Hydrocar5on Migration and its 'ear/surface .4pression, AAG Memoir ;;) +)

$l:-(:)

Maconald, #)'), D Jo&e, S) 2166:5) Lair of the A#ce Worm)


35/42

@KBrien, G)W), La!rence, G)M), Williams, *)R), Glenn, R), Barrett, *)G), Lech, M), d!ards,

)S), "o!le&, '), Boreham, ")J), Summons, ')) 2this volume5) The am+i Shelf, Bro!se

Basin, North-West Shelf, *ustralia * test-bed for constraining h&drocarbon migration and

see+age rates using a combination of ( seismic data and multi+le, inde+endent remote

sensing technologies)

@+sahl, S), D Benner, ') 2166:5) istribution and c&cling of terrigenous dissolved organic matter

in the ocean)'ature, (4;, 94-94$)

@r+han, >)J), %inrichs, R-?), Caull, ")R), Ta&lor, L)T), S&lva, S)C), D elong, )8) 2$1a5)

"om+arative anal&sis of methane-oxidi.ing archaea and sul+hate-reducing bacteria in anoxic

marine sediments)Applied and .n&ironmental Micro5iology, ;:, 16$$-16(9)

@r+han, >)J), %ouse, ")%), %inrichs, R)-?), McReegan, R)), D eLong, )8) 2$1b5)

Methane-consuming archaea revealed b& directl& cou+led isoto+ic and +h&logenetic anal&sis)

$cience, $6(, 949-94:)

Calmer, S)) 216695) ffect of biodegradation and !ater !ashing on crude oil com+osition) #n

@rganic Geochemistr& 2ds) M)%) ngel and S)*) Mac/o5) Ne! or/ Clenum) +) 311-3(()

Car/es, ')J), "ragg, B)*), Bale, S)J), Getleiff, J)M), Goodman, R), 'ochelle, C)*), 8r&, J)"),

Weightman, *)J), D %arve&, S)M) 216695) ee+ bacterial bios+here in Cacific @cean

sediments)'ature, (:1, 91-91()

Caull, ")R), Martens, ")S), "hanton, J)-C), Neumann, *)"), "oston, J), Jull, *)J)T), D Toolin, L)J)

216465) @ld carbon in living organisms and &oung "a"(cements from ab&ssal brine see+s)

'ature, (9$, 1;;-1;4)

Caull, ")R), ?ssler, ###, W), Boro!s/i, W)S) D S+iess, 8)N) 216635) Methane-rich +lumes on the

"arolina continental rise associations !ith gas h&drates) Geology, $(, 46-6$

35


36/42

Ceters, R)), D Moldo!an, J)M) 2166(5) The biomar/er guide inter+reting molecular

fossils in +etroleum and ancient sediments) ngle!ood "liffs Crentice-%all, #nc) +)

(;)

'ad/e, M) 216445) *++lications of aromatic com+ounds as maturit& indicators in source roc/s

and crude oils)Marine and etroleum Geology, 3, $$9-$(3)

'oberts, %)%), Sassen, '), "arne&, '), D *haron, C) 216465) 1(" de+leted authigenic carbonate

buildu+s from h&drocarbon see+s, Louisiana continental slo+e) 8ransactions / Gulf Coast

Association of Geological $ocieties, (6, 3$(-3()

'oberts %)%), Sassen, '), "arne&, '), D *haron, C) 2166a5) The role of h&drocarbons in creating

sediment and small-scale to+ogra+hr& of the Louisiana continental slo+e) #n Gulf Coast

Oils and Gases, in D3 $chumacher and +3 =3 er6ins, roceedings of the 'inth Annual

esearch Conference of the GC$$.M =oundation, $ociety for .conomic aleontolgy and

Minerology) +) (11-($9)

'oberts %)%), *haron, C), "arne&, '), Lar/in, J), D Sasson, ') 2166b5 Seafloor res+onses to

h&drocarbon see+s, Louisiana continental slo+e) Geo/Marine *etters, 1, $($-$9()

'oberts, %)%), D "arne&, ') 2166:5) vidence of e+isodic fluid, gas, and sediment venting on the

northern Gulf of Mexico continental slo+e).conomic Geology, 6$, 4;(-4:6)

'oberts, %)%), Wiseman, Jr), W)J), %oo+er, J), D %um+hre&, G)) 21666a5) Surficial gas h&drates

of the Louisiana "ontinental Slo+e H #nitial 'esults of irect @bservations and #n Situ ata

"ollection) #n Offshore 8echnology Conference aper O8C 10--0) +) 13)

'oberts, %)%), Rohl, B), Men.ies, ), D %um+hre&, G)) 21666b5) *coustic !i+e-out .ones7 a

+aradox for inter+reting seafloor geologicFgeotechnical characteristics 2an exam+le from

Garden Ban/s 1;15)roceedings / Offshore 8echnology Conference, (1, 361-;$)

'oberts, %)%) 2$15) 8luid and gas ex+ulsion on the Northern Gulf of Mexico continental slo+e

Mud-+rone to mineral-+rone res+onses) #n ")R) Caull and W)C) illon,'atural Gas

36


37/42

Hydrates: Occurrence, Distri5ution, and Detection, American Geophysical %nion3

Geophysical Monograph 1") +) 193-1;1)

'ueter C), 'abus, '), Wil/es, %), *ec/ersberg, 8), 'aine&, 8)*), Jannasch, %)W), D Widdel, 8)

216695) *naerobic oxidation of h&drocarbons in crude oil b& ne! t&+es of sulfate-reducing

bacteria)'ature, (:$, 933-934)

Sassen, '), 'oberts, %)%), *haron, C), Lar/in, J), D "hinn, )W) 2166(a5 "hemos&nthetic

bacterial mats at cold h&drocarbon see+s, Gulf of Mexico continental slo+e) Organic

Geochemistry, $, ::-46)

Sassen, '), Broo/s, J)M), Maconald, #)'), Rennicutt, ##, M)"), Guinasso, Jr), N)L), D 'eue


38/42

Sassen, ') 216665) Geolog& and Geochemistr& of gas h&drates, "entral Gulf of Mexico

"ontinental Slo+e) 8ransactions / Gulf Coast Association of Geological $ocieties, 96, 9;$-

9;4)

Sassen, '), Jo&e, S), S!eet, S)T), e8reitas, )*), Mil/ov, *)>), D Maconald, #)') 21666a5)

Thermogenic gas h&drates and h&drocarbon gases in com+lex chemos&nthetic

communities, Gulf of Mexico continental slo+e) Organic Geochemistry, (, 943-96:)

Sassen, '), S!eet, S)T), Mil/ov, *)>), e8reitas, )*), Salata, G)G), D Mcade )") 21666b5)

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OC$ eport / MM$, eport: 001/0)) +)6$-13

Sassen, '), S!eet, S)T), Mil/ov, *)>), e8rietas, )*), D Rennicutt, ##, M)") 2$1b5)

Thermogenic vent gas and gas h&drate in the Gulf of Mexico slo+e is gas h&drate

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de8reitas, )*) 2$1a5) Massive vein-filling gas h&drate 'elation to ongoing gas

migration from the dee+ subsurface in the Gulf of Mexico)Marine and etroleum Geology,

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e8eitas, )*) 2$$5) Gas venting and subsurface charge in the Green "an&on area, Gulf

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al/anes) #n ') *tlas,etroleum Micro5iology) Ne! or/ Macmillian, +) 1-;)

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+rofiler data from the Western North *tlantic)AAG +ulletin, ;1, ;64-::

?chu+i, ), S!ift, S)*), D 'oss, )*) 2166;5) Gas venting and late Vaternar& sedimentation in

the Cersian 2*rabian5 Gulf)Marine Geology, 1$6, $(:-$;6)

Wendt, J), Be/a, ), Raufman, B), Rostre!, '), D %a&er, J) 2166:5) The !orlds most s+ectacular

carbonate mud mounds 2Middle evonian, *lgerian Sahara5)2ournal of $edimentary

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the ocean floor and re+lenishing themselves in some reservoirsP $ea 8echnology, (4, 1-14)

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oxidi.ing and sulfate-reducing bacteria in association !ith gas h&drates from the Gulf of

Mexico) Geology, (, $(6-$9$)

hang, ")L), Cancost, ')), Sassen, '), Vian, ), D Mac/o, S)*) 2$(5) *rchaeal li+id

biomar/ers and isoto+ic evidence of anaerobic methane oxidation associated !ith gas

h&drates in the Gulf of Mexico) Organic Geochemistry, (9, 4$:-4(;)

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Acnow"edgements

Su++ort for this !or/ !as +rovided b& the e+artment of nerg&, Grant No) -

8G$-4;81(9;; and ?)S) e+artment of nerg& Grant No) -8"$;-NT96$

through the ?niversit& of Mississi++i to Jean Whelan and7 Gas 'esearch #nstitute

"ontract G'#36:$;(:4: to Larr& "athles, "ornell ?niversit& !ith a subcontract to

Jean Whelan) Than/s to Jean-Cierre %ou.a& and 'oger Summons, for hel+ful comments

on the final manuscri+t) ncouragement and man& useful discussions !ith Reith

Rvenvolden, "huc/ Rennicutt, 'oger Sassen, "hris Martens, Mi/e Whiticar, *lan Judd,

and 'ich "amilli are gratefull& ac/no!ledged) Man& than/s to the outstanding cre! of

the '> d!in Lin/ and the Johnson Sealin/ as !ell as great shi+mates 2Laura La+ham,

Jeff "hanton, #an Maconald, #ra Leifer) 'ic/ "offin and Ren Grabo!s/i among others5

for contributing to the ideas +resented here)

surface and subsurface manifestations of gas movement through a n-s transect of the gulf of mexico ...

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