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SPE 28507

Soc iety of PetroleumEr@news

State-of-the-Art Survey on Hydrate FormationM.A. Hight, Texaco Inc . rICopyr ight 19S4, Sedety of Pet ro leum Engineers , Inc .TIM pape r wss pr epa red for presenta ti on at the SPE 69 th Annual Techni ca l Conf erence end Exhi bit ion he ld in New ~l eans , ~ LJ.SJL, 25 -26 SaPt ember 1994This papar was ealactaci for presentat ion by an SPE Program Commlttae fol lewing rev iew of information conta ined in an abstract submi tted by the author(a) . Contents of the paper ,as presented , have not b%enreviewed by the sec ie ty of Pet ro leum Engineers and are subject to cer recf ion by the author(s) . The material , as presented, cfces not nacesaari ly ref lectany posit ion of the ~ ie ty of Pet ro leum Engineers , i ts off icers, or membm. Papers preeanted at SPE maat ings are aubjact to publica tion rev iew by Edi torial Commi ttWa of the Socie tyofpet ro leum Engineers . permiss ion toCOPYisrestr ic ted toan abafracf ofnotmore than ~ w~ds. I llua trat iona may not ~ COP~ The a~ra~ shoufdcont~n ~nsPic@Jus ackn0w~9mentof where and by whom the paper is presented. Write Librarian, SPE, P.O. BOX 833S36, RlchardWn, TX 75~3-3SW. U.S.A. Teiex 1W45 SpEUT.

AbstractThe formation of hydrates in wells and pipelines canseriously hamper production operations since hydrates... ., .I:___ T1..a a.rnntinn (-if hvd[~~~~can completely mock fiOwIIIIe> III= ,Ull, lull=,, ~ ,.,is due to the presence of water along with certain lowmolecula r weight gases. To avoid hydra te b lockages it isimperative to first know under which temperature andpressure conditions hydrates will form. This can bepredicted by computer models based on the fluidc omposition. This study predic ts hydrate formationconditions for a range of live o ils by computer simulationand determines the sensitivity of several physicalproperties.

IntroductionHydrate formation occurs in the presence of water a longwith certain low molecular weight components that arec ommonly found in petroleum produc tion. Hydrate-forming gases that are c ommon in reservoir fluids aremethane, ethane, propane, butane, nitrogen, carbondioxide, and hydrogen sulfide. Hydrates are solid crystalsof water that form around sma ll vapor molecules. Theyform as hydrogen-bonded water molecules in the form ofcages trap the ga s molecules inside. These single solidcrystals propagate until large crystal masses have formed.Hydrates have physical propetiles similar to ordinary ice,except tha t they form at tempera tures much higher thannormal freezing conditions. As with ice, the waterexpands as it changes from a liquid to so lid sta te,

therefore causing the same types of problems as withwater lines in winter conditions.in order to avoid hydrate problems it is imperative tofirst know under whic h ?ew,perGfwe and pressureconditions hydrates will fo rm. The hydrate formationconditions are dependent upon the fluid composition, *,- ~----:cnm. h,,and can be determmeci nom me ~urrlpuwlw[ t- ~,computer models. Hydra te formation conditions canthen be compared with the pressures and temperaturesexpected in the wells and flowlines. If operatingconditions will be in the hydrate formation region, thenp lans to prevent hydrate formation can be made.One way to prevent hydrate blockages is to avoid thetemperature and pressure conditions under which theyform. This can be accomplished by insulating or buryingpipelines to reduce hea t losses and sizing flowlines toma intain higher flow veloc ities and reduce pipelineresidence time. However with deeper reservoirs, theresulting fluid flow paths become so long that atremendous range of pressure and temperatureconditions are encountered and this method is notfeasible.O ften hydra te cond itions cannot be avoided and otherprecautions must be taken. These inc lude removal ofwater or removal of hydrate-forming components, oraddition of hydra te-inhibiting chemicals. wfJ terremoval usually requires the additional handling oflarge amounts of produced water which for offshoreoperations often means separate flowlines and may

References and illustrations at end of paper 439

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2 STATE OF THE ART SURVEY ON HYDRATE FORMATION SPEM be ecmmh h mg dktmces Removal ofhydrate-forming components invorves Iowefing thepressure to release the light components from the heavierliquid components and usually requires subsequentcompression and/or pumping to transport the fluid longdistances from the separation point. The addition ofhydrate inhibitors is successful, but expensive andincreases environmental problems. Classicalthermodynamic hydrate inhibitors tha t have been usedsuccessfully are sodium chloride and other electrolytes,methanol and monoethylene glycol. These are useda lone or in combination with each other.Remova l of hydrate-forming components by separationwill not be a complete removal and therefore will tendonly to shift the equilibrium line at which hydrates willform. For lighter reservoir fluids this separation willprobably not be benefic ia l. For heavier fluids, separationmay reduce but not eliminate the need for inhibitors.Two types of chemical inhibition have been developedfor the petroleum industry. The first, referred to asthermodynamic inhib ition, is based on a shift in the phaseequilibrium to pressures and tempera tures outside thefield operating conditions in order to avoid the formationof hydrates. The second method, called kinetic inhibition,dea ls with affecting the crysta l growth rates so that onceformed, small hydrate crysta ls will not agglomerate andc an move along with the fluid stream without formingblockages.Thermodynamic inhibitors have been used successfully formany years a ithough cosis can be proiiibitiw, espec ia llyfor moving fluids long distances from offshore areas.Quantities of methanol required a re often in the range of20 to 30 weight percent methanol in the water phase.Kinetic inhibitors will be needed in orders of magnitudesmaller quantities, but the chemicals and methods arestill in the development and testing phases. Limits ofeffectiveness are not yet defined to the point of practicalapplication without high risk.The mechanism of thermodynamic inhibition stems fromthe increased competition for the water molecules by theinhibitor molecules or ions. In order to be effective,inhibitors must be in the liquid water phase. Any volubilityin the vapor or liquid hydrocarbon phases must beac counted for and considered in calc ulating inhibitorrefi:]irements.- =-.. . . .. ... .

BackgroundPetroleum-related hydrates belong to either of two crystalstructures, called structure I and structure Il. On amolecular basis, these crystals contain at least 85 percentwater. The three basic cavities that compose these twostructures are pictured in Figures 1 as presented bySloan(1). The apex of each angle represents a watermolecule and the lines between them representhydrogen bonds. Structures I and II in are c omposed ofmixtures of the three cavities. Cavity (a ) is considered a

small cavity and the two others are largeCavity (a) in Figure 1 is c omposed of five-sideand there are twelve of these faces. Thus thisthe notation 512. Cavity (b) a lso has twelvefaces but has a six-sided face on both the topbottom of the cage. It is denoted 51262. Cavifour six-sided faces in addition to the twelve sand is labeled 51262.Ths .mr-rll m-jvitv iS the basic building block,,, --,..-. .- ....,structures. Structure I is composed of twoc avities and six of the 51262 cavities. Struccomposed of sixteen of the 52 and eight ofcavities. In structure L the 512 cavities are linkethe vertices and in structure II the 512cavitiesthrough face sharing.These cavities are not stable as pure water.larger than ice cavities and will collapsesupported by the presence of guest molecula rge percentage of the cavities. If hydratecomponents are ava ilable. they will fill the castabilize the hydrate crystals.The occupation of hydrate cavities is determinlarge degree by the size, c hemical nature, aof the hydrate-forming guest molecule. Theof hydra tes occurs at an interface of hydrocarand liquid water. This can be either a free-ginterface, a liquid hydrocarbon-liquid wateror a fluid hydrocarbon-adsorbed water interfato the limited solub ilities of hydrocarbons andeach other, fermcdior of hydrates in either thehydrocarbon liquid is unlikely.Small cages must be filled by sma ll moleculesmethane, nitrogen and hydrogen sulfide.components methane, ethane, c arbon dioxhydrogen sulfide will each form structure I hydrmixture, however, structure II hydrates will uformed with the smaller molecules the smaland stabilizing the hydrates with la rger molecuas propane and iso-butane in the larger cavitieThe rate of hydrate formation in processing eand pipelines is largely unknown. The effectvelocities and flow regime also remaininvestigated. Since hydrate formation takeswater-hydrocarbon fluid interfaces it fo llowsregime will affect hydrate formation tendencies

Hydrate Curve GenerationThe purpose of this portion of the study is tohydrate equilibrium curves for a variety ofobserve whether a trend exists based on someor chemical property of the fluid. If trends canthen a generalized curve or equationueveioped to predic t hrydrate kiirn@~fibased on a single fluid property. Thisapproximate information useful for screening

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SPE28507 MARGARET A. HIGHTwhen detailed information is not needed or is notavailable.Each hydrate equilibrium curve represents the pressureand temperature c onditions under whic h hydrates willform if free water is present. Each hydrate locus is a curvewith temperature a long the x-axis and pressure a long they-axis. The pressures and temperatures making up theregion to the right of each curve is the hydrate-freeregion. All the conditions to the left of the curve lie in thehydrate-forming region.These hydrate curves are useful in conjunction withhydraulic simulation of wells and pipelines. The hydraulicmodels will predict pressures and temperatures all alongthe fluid flowpaths for the various ra tes, water cuts, andcompositions to be expected. Plotting the pipeline orwellbore conditions on the hydra te plot will show underwhich conditions and in which locations hydra tes can beexpected if the hydrate-forming region will be entered.

Computer Simulation ModelA commerc ially ava ilable c omputer program was usedto generate hydrate curves based on the fluidcompositions. The program is written specifically topredic t hydrate formation in mixtures of iiyr5~OC~ibO~Sand associated materials. The program can be used topredic t hydra te forming conditions in the presence of anaqueous liquid, a gas, and/or a non-aqueous liquid. Theprogram is a state-of the-art program that will predic t theentire hydrate formation pressure-tempera ture locuseither with or without inhibitors.The base program is based on the scheme suggested byParrish and Prausnitz (2), which was modified andextended by Ng and Robinson (3,4). The gas hydrateroutine is based on a procedure developed by Ng andRobinson (5). The Peng-Robinson equation of state (6) isused for all property calculations throughout.The program allows fluid streams to be defined with asmany as 20 components. The components may consist ofdisc rete c omponents as well a s petroleum frac tions orpseudo-components. The program has a database of 28pure components including those common tohydrocarbon reservoirs. This model has previously beenvalidated against laboratory data for severa l o f the fluidspresented in this study.

Fluid CompositionsHydrate curves were generated for seventeen differentreservoir fluids representing a range from black oil fluids togas condensates and dry gases. Figure 2 presents thephase envelopes for some of the fluids to show the rangeof fiuids used. The compositions of Yhe fluids sfudiea areshown in Tables 1 to 3, respectively for dry gases, gascondensates and blac k oils. Physic al properties for a llfluids are shown in Table 4.

Hydrate CurvesHydrate equilibrium Curves have been generated fthe compositions desc ribed in Tables 1 to 3. These ashown in Figures 3 to 5. The region to the right of eaccurve represents the hydrate free region. The a reathe left represents the conditions under which hydratewill form. The point at which the slope of the curvchanges sharply is the bubble point. The curve belowthe bubble point represents the presence of two liquiphases (hydrocarbon and water), hydrate crystals, anvapor. The curve above the bubble point representhydrates p lus the two liquid phases. This portion of thcurve is a stra ight, nearly vertical line tha t shows velittle pressure effect on the hydrate formationtemperature. The Garden Banks fluid because ofintermediate gravity is plotted on all hydrate curve(solid black line) for easier comparison from one setcurves to another.Figure 3 displays the hydrate equilibrium curves for athe dry gases. These curves fall into two groups: onwith hydrogen sulfide and one without. The sour gacurves lie from 20 to 28 degrees to the right for thsame pressure than the other gases. The sour gases caform hydra tes a t 88 to 90 OFdegrees over a wide rangfif mr=~~w-c Tha , U. A . .II m ~CiSjOii iG?KM Cd ~~percentage of hydrate forming components presentthe fluid stream.Figure 7 shows hydrate formation tendencies of some othe hydrate-forming molecules when they are presen

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4 STATE OF THE ART SURVEY ON HYDRATE FORMATION SPE 28507as pure components alone. Tables 1to 3 show that allfluids except North Arne and the dry gases nave from 44to 87 mole percent methane and all have from 3 to 10percent ethane.Table 1 shows that the sweet dry gases have over 75mole percent methane and about 90 mole percentcombination of methane, ethane and propane yet thehydra fe formafion tendenc ies are much d ifferent than forthe pure components. At a pressure of 2000 psia thesegases will form hydrafes at 68 to 70 F yet the purecomponents form hydrates below 60 F at this pressure.The sour gases all contain about 30 mole percenthydrogen sulfide and over 30 mole perc ent methane. Acomparison of these curves with that of pure hydrogensulfide shows the same trend with the same shape ofcurve and the same shift to the right from the other curvesthat have no hydrogen sulfide.This difference in hydrate formation tendencies betweenpure components and mixtures has a lso been observed inIaborafory work. Dramatic increases in hydrate stabilitieshave been observed with the addition of larger-moleculegases to methane gas. As pure components, the smallmolecules (methane, ethane, carbon dioxide, andhydrogen sulfide) will form Struc ture I hydrates, but inmixtures will form Structure II hydrates. These purecomponent hydrates are formed with only one size cavitybeing occupied. With mixtures, both the la rge and sma llcavities will be occupied and this appears to lendstability to the hydrate crysta ls. A lso certa in componentscan act as help gases to increase the hydrate-formingcapab ility of other components. This has been observedwith both oxygen and nitrogen.One fac t became appa rent in surveying the results. Thatis that the total fluid stream properties must beconsidered rather than just the vapor phase or the APIgravity. The interac tion between the liquid and vaporstream is important, even though the hydrate-fo rmingcomponents will be in greater concentrations in thevapor phase. None of the Table 4 properties of theseparate vapor and liquid phases could be consistentlycorrelated with the hydrate equilibria.In order to study some of the differenc es between thevapor and the wellstream reservoir fluids, a processsimulator was used to generate compositions of four ofthe fluids separated at standard conditions. Thesecompositions are shown in Table 5. Only the vaporcompositions were used to genera te hydrate curves forthese fluids. The fluids chosen for these runs were thosewith lower percentages of light hydrocarbons.

Figure 8 is a plot of the hydra te curves for Ha ra ld, N. Arne,Garden Banks, and Ewing Banks. Both c urves from theccmap+nr vrmnr CQrnpQSiNQnS (TQble ~) and the reservoir,y ---- .-r-.compositions are shown. Theserange of 0.7 to 0.93 specific------- **L_ .---m, ..:.repw3seril f~u,~~111= Ie>clvull

fluids represent a vaporgravity. The solid lines

+hc.n~ ,, ,= Antt*r4 inesl r-

represent the separator vapor. Figure 9 shows the sa---..14- -- - . -i laIeauli> Ull u >el I mug p d.The four fluids shown all have low percentages oflight hydrocarbons before separation. The vapor strec ompared to the two-phase stream shows a greatendency for hydra te fo rmation in a ll cases. ResultsN. Arne indic ate a change from the least tendencyhydrate formation to the greatest of the four fluids wseparation. The other fluids exhib it the same trenddifferent magnitudes of c hange. N. Arne may exhdifferent behavior because its composition isadequately defined since the reservoir fluid haspercent C7 plus components and it has the largchange in its bubble point.If N. Arne is neglected, the other three fluids showdecreasing tendency for hydrate formation wdecreasing vapor specific gravity. This cancompared with Figure 10 which is a published chartof hydrate-formation tendencies based on gas specgravity. The c omparison, with an expanded sc aleshown in Figure 11. The solid dashed lines represespec ific gravities of 0.7, 0.8, 0.9 and 1.0. These resind icate good agreement, with the la rgest d ifferenbeing only one F for the Ewing Banks fluid . This limitsampling of data indicates that separator vaspec ific gravity can charac terize hydra te forma titendencies as long as this information is not usedcharacterize full wellstream data.Figure 12 is a semi-log plot of the six gases comparwith the hydrate predic tion for gases. The symbrepresent the three sweet gases and the dashed lrepresenf the hydrate prediction chart lines.Brooke land line is slightly above where it should be fospecific gravity of 0.726. W. Swan (specific gravity 0lies on the 0.60 line and Wiison Ranch (gravity 0.6.4)in between 0.60 and 0.68. The order of the two gasereversed from what the specific gravities would predThe three sour gases in the lower portion of the plotwell below the 1.0 line even though their specgravities are only slightly greater than 1,0.Of the eleven hydrate curves characterizingcondensates and black oils, the only property tcorrela tes well with the hydra te forma tion tendencythe molecular weight of the total fluid stream.similar hydrate curves shown in Figures 4 andrepresent a range of fluid molecula r weights from 2978. Shasta (molecular weight = 29) has one oflowest molecular weights and shows the greattendency for hydrate formation, N. Arne onopposite end of the scale has a molecular weight189 and the least tendency for hydra tes. Ewing Ba>~th~ meiecuiar w-iriht nf 147 fa lls in between N. A..-. V... -. . ..and the lighter fluids. Garden Banks with a molecuweight of 79 fa lls just to the left of the 31 to 78 range.With seven curves behaving simila rly, enough dataava ilable for a good curve fit. An exponential c urveof h~ a=van.,- . ,, S m br f ikk ShOWd the followi

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.SPE28507 MARGARET A.

regression data listed in Table 5. The data from Haraldand Green C anyon fluids were not used in the curve fitabove the bubbie pOh~. The i~Wlhil~ CApUl I-I I IS cm .. Ra. antshown in the Table 3 for the equation where y representspressure in psia and x is the temperature in F.

y = aebxThe exponents from the individual curve fits wereaveraged. The resulting plot of the generalized curve isShown in F&W= I ~a ~ng with the Sta ffjord and Va ldemarfluids. The curve is about 1 degree off for the average inthe pressure range up to 2000 psia . Above this pressurethere is a greater deviation from the high side and the~uwe fl? is neariy the same as the IOW curve. However, it ison the conservative side at points where it does devia te.For comparison the equations with the highest and lowesta-values are also plotted.

Separation EffectsSince hydrates are formed at the interface betweenhydrocarbon phases (either vapor or liquid) and the freewater phase, it follows that vapor-liquid separation willa ffect hydra te formation tendenc ies. Predic tions weremade for three fluids sepa ra ted a t pressures of 100 and1300 psia.Figure 14 shows the difference in hydrate tendenc ies forthe Shasta fluid on sepa ra tion at 100 and 1300 psia . Thesolid line represents the reservoir fluid before separation.The dashed lines show the liquids at the two separatorpressures and the dotted lines show the vapor streams atthe two pressures.The vapor curves show an increased hydrate tendency ofabout 1 degree for pressures above 500 psia. Theseparator pressure makes no appreciable difference. Theliquid curves show less tendency for hydrates by 1 degreefor the higher pressure and 3 degrees at the 100-psiasepa ra tor pressure when compared with the reservoirfluid.Separation effects for the Statfjord fluid are shown inFigure 15. Separation at 1300 psia shows less than 1degree change for both the liquid and vapor streams. At100 psia, separation shows a 3 degree shift to the left inthe liquid hydrate equilibrium curve and 1 degree shift tothe right for the vapor line.A ll liquid streams in Figures 14 and 15 have bubble pointsabove 2000 psia and hydrate curves below this point arebased on a two-phase hydrocarbon stream. Both fluidshave methane concentrations above 50 mole percent atboth pressures, therefore keeping the bubble points high.The presence of other hydrocarbons along with methaneincreases the stability of the hydrate crystals.Figure 16 shows separation effects for the Garden Banksfluid. In this case, bubble points for the liquid stream areshifted to below 1200 psia and there is a significant shift tothe left in the hydrate equilibrium line. Curves are shifted

HIC;HT 5by as much as 18 degrees for the 100-psia separationand seven degrees for the high pressure sepa ra tion.hese are offset somewhat by the shift to the right in theequilibrium line for the vapor curves by as much as 4degrees at some pressures for the low pressureseparation and about 1 degree for the 1300-psiaseparation.These separator curves show that for compositionswhere separation can result in a significant reduction inthe bubble point, a decrease in hydrate formation~emlPe:aydre~ can be ~xp~cted for the liquid stream.This will be partia lly offset by an increase in the hydrateformation temperature in the vapor stream.

ConclusionsOf the eleven gas condensates and blac k oilsevaluated, seven had hydrate formation curvesthat were within 1F of each other for a givenpressure below the bubble point. Molecular weightsof these similar fluids ranged from 31 to 78.Full wellstream fluids cannot be categorized by thespecific gravity of the vapor since liquid, if present,will influence hydrate formation tendencies.Of the properties studied , the property which bestcategorizes hydrate formation tendency is themolecula r weight of the fluid inc luding both liquidand vapor phases.If vapor-liquid separation can result in a significantreduction in the bubbie point, a de~ease inhydrate formation temperatures can be expectedfor the liquid stream. This will be partia lly offset byan increase in the hydrate formation temperaturein fhe vapor stream.Hydrate tendencies of light hydrocarboncomponents in a mixture are much different thanthe tendencies for the components if pure. Thecomponents influence each other and can cause achange in the type of struc ture formed and in thestability of the hydrate crystals.Hydroaen sulfide has a dominant effect on sourgases-and results in hydra te equilibrium curvessimilar to pure hydrogen sulfide.

References1 Sloan, E.D., J r., C la thra te Hydrates of NaturaGases, Marcel Dekker, Inc., New York, 19902) Prausnitz, W.R. and J.M. Prausnifz, *DissociationPressure of Gas Hydrates Formed by Gas Mixtures. IndEng. Chem. Process Des. Develop., 11, 26(1972).

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6 STATE OF THE ART SURVEY ON HYDRATE FORMATION SPE285073) Ng, H.-J . and D.B. Robinson, The Measurement andPrediction of Hydrate Formation in Liquid Hydrocarbon-Water Systems, Ind. Eng. Chem. Fund., 15, 293(1976).4) Ng, H.-J . and D.B. Robinson, The Pred ic tion of HydrateFormation in Condensed Systems, AIChE J ., 23, 477(1977).5) Ng, H.-J . and D.B. Robinson, Method for Predic ting theEquilibrium Gas Phase Water Content in Gas-Hydra teEquilibrium, Ind. Eng. Chem. Fund., 19, 33(1980).6) Peng, D.-Y., and D.B. Robinson, A New Two-ConstantEquation of State, Ind. Eng. Chem. Fund., 15, 59(1976).

Table 1 ICompositions for Dry GasesI Brook I w Sw I W Ran I Aker C. B. I NealC02 4.70 I 8.21 I 0.67 I 3.15 I 5.98 4.97I I I

N2 0.59 I 0.46 I 0.05 2.50 6.18 I 1 441 I I IH2S I 0.00 I O.(XI I 0.00 I 33.50 I 29.20 I 38.50 I

C2 I 10.38 I 4.97 8.80 6.48 9.04 I 6.75I I I IC3 ] 3.48 I 1.29 I 1.91 I 9.62 I 8.19 \ 10.23 Ii-C4 0.64 I 0.19 I 0.26 1.08 1.37 ~ 1.42I I I In-C4 I 0.96 I 0.24 ] 0.29 ] 1.34 1.83 I 1 56I I I Ii-C5 I 0.32 I 0.07 I 0.09 I 0.51 I 0.50 I 0.53 In-C5 0.24 0.05 0.04 0.49 0.61 0.571 I I 1 I i IC6 I 0.12 I 0.08 I 0.06 I 0.46 I 0.58 0.61

I I IC7 I 0.06 I 0.09 I 0.07 I 0.11 0.26 I 0.48 IC8 I 0.07 I 0 00 I o oo I 0 2 I 0 27 I 0 49 I

Table 2Compositions for Gas Condensates

Shas Stat. Ersk Vald Jolt. G.C. Ha1 1 i I

i C02 I 0.919 1.144 4.78 1.19 I 0.17 I 0.05 I 1.11 I I I61.66 I 52.38 I 44.I C2 7.15 7.654 10.73 7.116 I 7.81 I 3.86 I 7.71 II C3 I 4.49 3.864 5.11 I 4.726 4.35 5.16 I 7.0I i-C4 0.613 0.564 0.99 0.600 0.95 1.59 1.31 [ I I 1 1 1I n-C4 1.634 I 1 479 1.76 2.150 2 00 3.17 3.2I I I 1 1 I I Ii-C5 0.409 0.338 0.79 0.950 0.84 I .86 0.9

n-C5 0.715 0.661 0.89 1.550 1.15 2.11 1.5

I C6 I 1.022 0.783 1.29 I 2.150 I 1.91 4.13 I 2.5I C7+ 6.946 6.868 10.88 16.69 18.52 25.60 26.

Table 3Compositions for Black/Heavy Oils

Brent G.B. N. A me I E. BanC02 1.93 Occ l

C2 I 9.58 I 6.75=aa=-C4 I 3.5 I 2.25=&&6 I 2.18 I 2.85C7+ 72.79 I 23.47

2.94 I 3.32

--t+

2.160 1.421.m 0.861.290 0.682.700 1.7971.137 37.45

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SPE28507 MARGARR A. HIGHT 7

Table 4Properties at Standard Conditions

Vapor Liquid Total StreamGOR

Fuid sp . G r. Mc sp. ~~ &@ Wt M ol Wt SCF/BBrook 0.7266 21.05 - - - -W.sw 0.6846 19.8 - - - -

W. Ran 0.6359 18.5 - - - -Aker 1.000 29 0C.B. 1.04 30.2 - - - -Neal 0.189 31.6 - - - -

Sha sta 0.7370 21.35 0.748 125.54 29.00 9964Stat 0.7102 20.58 0.8035 156.99 30.71 8447

Erskine 0.8321 24.11 0.7852 162.02 40.13 4874Vald. 0.8297 24.04 0.7496 192.42 53.93 2386

Jell 0.7574 21.94 0.8451 214.79 62.69 1945G.C. 0.8289 24.014 0.8261 166.74 69.66 1393Har. 0.9356 27.11 0.07456 187.62 78.22 1123Brent 1.1239 32.561 0.8639 241.22 72.68 1983G.B. 0.7916 22.93 0.8728 228.14 79.46 1331

N. Am 0.8470 24.54 0.7627 231.41 189.27 111E. B. I 0.7001 I 20.284 0.9333 I 331.53 ] 146.84 ] 544

Table 5Vapor and Liquid Compositions of Separator Fluids

1 1 I IComp Harald N. Ame Ga rd en B. Ewing B. , 1 I 1I Vap. Liquid Vap. Liquid Vap. Liquid Vap. Liqu

~02 2.221I 0.038I 1.X6 I 0.02,10.00 I 0.00 I 0.350 I 0.00\2 1 709 0.003 0.879 0.002 3.452 0.004 0.674 0.03c1 65.44 0.471 69.00 0.504 74.55 0.417 85.401 0.55h2 I 11 31 0.472 i 12.42 I 0.521 I 9.194 t 0.343 5.449 I 0.21k3 I 9.671 I 1.502FC4 1 614 0.649C4 3.744 2.165 C5 0.8142 1.261 I.386 1.458+1.567 0.6303.262 1.879-

+0.704 1.4400.461 3.284

=-k=+1.424 0.5412.548 1.469E5.lE+1.025 I 7.633

1.707 I 1.00

0.466 ] 0.99

-4=

I Table 6Regression Dat for Exponential Curve Fitof Seven Similar Hydrate Formation CurvesI Corr I I I Number mid I Coef ll. la I ofpoints

Statfjord 0 9934 0 0;37 5 829 31Erskine 0.9942 0.0897 4.257 41Valdemar 0.9968 0.0848 5.596 26Joliet 0.9977 0.0837 5.9054 25Gr. Can. 0.9996 0.0841 5.358 20Brent 0.9960 0.0900 3.902 34Haald 9996 853 4 898 2

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8 STATE OF THE ART SURVEY ON HYDRATE FORMATIONSPE 28507

Figure 1. Hydrogen-Bonded Water CaviU* thatform Clathrate Hydrates

@@@

a b cSmall Cavity Large Cavities

Figure 3. Hydrate EquilibriumCurvesfor Dry Gases

immE~ 1,s00l:~>y~ ::d

a4Gsow~@J SJ

Figure 5. Hydrate EquilibriumCurvesfor Biack OilS

Figure 2. Phase Enveiope for FiuidsStudied

Figure4. Hydrate EquilibriumCuwes*fir e-e r mwhnsatasIur w r]ii /)

I

I:~- & ~40 mTanpombmq

G.MbE18khe.. . . . .H9dd-.

St811im-dshL

Wdanm.bIliOl-

G. CUW

Figure6. Phase Enveiope for Gases

~

/220- p

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- SPE28507 MARGAR~ A. HIGHT

Figure 7. Hydrate Equilibriumfor Pure ComponentsCurves

IiII

~ J.--------.V...7---770s0. impuduro,q F

.. .ManmO

Etharm. . .. . .ProplmeNtiOgenCarbonD*-..3uUii--G.Eants

Figure 9. Log Plotof Reservoir Fluid vs.separator Vapor Hydrate Curves

Y E

*M201YI - N. Arm..:I,ooo - :9: G. Sdm

gw : ,w.&..;.*.;D E. Emnluti. :. a

jm ;,r...,..,.- mm* :. .0 .

;/

..:0. N.km, -. @ . .. . .100 .*.*::O.

G. Sao m..*e

50 E. Banks30 40 50 60 70Tunpodum d~ F

Figure 11. Log Plotof Reservoir Fluidvs. Separator Vapor Hydrate Curves

A Harold-.,.. .. G. Banks. . . . . . _. . . .. -- -., . . , , e =-... KS---40 45 50 55 w

Figure8. Reservoir Fluid vs.Separator VaporHydrate EquilibriumCurvesam, , I ,-,--- m * e= Oti2 1V _2,500 - :e9 N.km::g z ,~ - 9 G. S8nlfs= ,%0@g 1,500 - E. Sanka:%* i ,=.. Maid& I,ooo - N.&m. .. . .5W - . ,**ws@@:$ ...*..G. sank=Om E. Sanka40 xl m 70.- Tonq)omtum dq F 1 I

Figure 10. Pressure-Temperature Curves forPredictingHydrate Formation~I .000 I I I /1 /,.u6U6111.

Figure 12. Hydrate EquilibriumCurvesfor Dry Gases:-F -..-...200 ..*.::: ....-.:- ..... ..-.. 1 0 L.Swan...........*..--....-........ W. R;nchlCO - . . . . .BfookkNMl

50 -An 45 50 55 m

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.10 STATE OF THE ART SURVEY ON HYDRATE FORMATION SPE28507

Figure 13. Comparisonof Actual Hydrate Curveswith Curve-fit Data

:R =.500-/ L_bhf . . .. ..& 1,000 - -.Soo -

0 40 50 60 70

P. ---- . L- -Au -.4 U.,A.Aa m ,Fune fnr RrmnrvnirFigure la. akmp u nyui am UUI r=- IWO -.-- . . . . .and Separator Fluids

\ II*. -rUquid @

II?52 Iooo 40 Ea 60 m 1-aTunpuatum.dw F

Figure 14. Shasta Hydrate Curves for Reservoirand Separator Fiuids

:-HK=i,

40 mIII&turo,qfWF

Figure 16. Garden Banks Hydrate Curves forReservoir and Separator Fiuids3.oal I

Y :6i

Y n

No ~p..: i _2,S00 - 4 .f

; Uq@d @j z,~ - ; {: yl~a 4 /. 4t Vapa @f 1,s00 - ..*.

P=1300i ----4 n.jg 1,000 - .;...-

~ qula gg

J .D..e. P=looS20 - 4::. . .~-e:=. Va--w-@P=loo

o 40 m T=. dwwF