Resumo:
The stabilityo f submarineg ash ydratesis largelyd ictatedb y pressurea ndt emperature,
gasc ompositiona,n dp orew aters alinity.H owever,t he physicapl ropertiesa nds urfacec hemistry
of deepm arines edimentms ay alsoa ffectt he thermodynamisct ate,g rowthk ineticss, patial
distributionsa,n dg rowthf ormso f clathratesO. ur conceptuaml odelp resumesth at gash ydrate
behavesin a way analogousto ice in a freezings oil. Hydrateg rowthi s inhibitedw ithin finegraineds
edimentbsy a combinatioonf reducedp orew atera ctivityi n the vicinityo f hydrophilic
minerals urfacesa, ndt he excessin ternale nergyo f smallc rystalsc onfinedi n pores.T he excess
energyc anb e thoughto f asa "capillaryp ressurei"n the hydratec rystalr, elatedt o the pores ize
distributiona ndt he stateo f stressin the sedimentf ramework.T he baseo f gash ydrates tabilityi n
a sequencoef fine sedimentiss predictedb y our modelt o occura t a lowert emperatur(en earert o
the seabed)t han would be calculatedf rom bulk thermodynamice quilibrium.C apillary effectso r a
buildu p of salti n the systemc ane xpandth e phaseb oundaryb etweenh ydratea ndf ree gasi ntoa
divariantf ield extendingo ver a finite depthr anged ictatedb y total methanec ontenta ndp ore-size
distributionH. ysteresisb etweent het emperatureosf crystallizationan dd issociatioonf the
clathrateis alsop redictedG. rowthf ormsc ommonlyo bservedin hydrates amplesre coveredfr om
marines ediments(n odules,a nd lensesi n muds;c ementsin sands)c an largelyb e explainedb y
capillarye ffectsb, utk ineticso f nucleationa ndg rowtha rea lsoi mportantT. he formationo f
concentrategda sh ydratesin a partiallyc loseds ystemw ith respectto materialt ransporto, r where
gasc anf lusht hroughth e systemm, ayl eadt o waterd epletionin theh osts edimentT. his" freezedrying"
m ayb e detectablteh roughp hysicacl hangetso thes edimen(tl ow waterc ontenat nd
overconsolidationa)n d/orc hemicala nomaliesin the porew atersa nd metastablep resenceo f free
gasw ithint he normalz oneo f hydrates tability
