Hw 1 Solution

1. How do you perform a systematic ow assurance assurance analysis analysis for a typical subsea subsea eld development? Ans: Following steps are to be followed for ow assurance analysis for a typical subsea eld. Collec Collectt a reser reservoi voirr uid uid sampl sample e !"is !"is is done done by sample sample drilling drilling in t"e reservoir. #redict p"ase be"avior prediction of p"ase c"aracteristics$ w"ic" includes predicting predicting proportion of li%uid and gas in t"e reservoir uid and its be"avior at di&erent temperature and pressure pressure conditions. 'ariation 'ariation wit" time is also ta(en into account. )ene reservoi reservoirr performan performanceit ceit includes includes predict predicting ing product production ion prole prole of  reservoir over time and c"ange in temperature and pressure of reservoir. #erform t"ermal"ydraulic analysis at various segments of system suc" as well"ead$ ow line$ risers etc. )evelop )evelop system system design design based on previous previous steps steps nal system design is prepar prepared ed w"ic" w"ic" includes includes specicat specications ions for various various component components s suc" suc" as riser$ well"ead and Flowline and also re%uirement of pump$ in*ecting or "eating systems. +mplementation of monitoring program is necessary to be able to be aware of any unforeseen events eg. #ump failure$ in*ector failure etc. Consider contingency plan for remediation$ it means$ planning for t"e steps to be ta(en under unforeseen conditions. )etermine ,&ect of c"anges in uid properties and composition over time. •

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-. ,plain in detail t"e t"ermal modeling tas(s tas(s or calculations calculations in ow assurance. assurance. Ans:  !wo  !wo types of t"ermal t"ermal modeling modeling tas(s are are performed in in ow assurance assurance 1. /teady /teadyst state ate t"erma t"ermall modelin modeling g 0 +t consists calculation of owing ell"ead !emperatures 2FH!3. Aim of  steady state analysis is to deal wit" various ow assurance related issues under normal operating conditions. !"is issues are "ydrates$ asp"altenes$ salt deposition$ erosion etc. !"ese issues are sub*ected to specic temperature and pressure ranges in t"e uid. 4y performing t"ermal modeling$ steps can be ta( ta(en to (eep eep t"e t"e uid uid out out of dang danger er 5one 5one and and prev preven entt t"es t"ese e ow ow assurance related issues. -. !ransient ransient t"ermal t"ermal modeling modeling 0 it consis consists ts calcul calculati ation on of Coold Cooldown own time time after after s"ut s"ut down down and ow line line warmup warmup time calculati calculations ons at start start up. !"e temperatu temperature re conditio conditions ns during during t"ese events can be %uite di&erent t"an t"e normal operating conditions.  !"erefore$  !"erefore$ it is necessary to predict predict uid be"avior under t"ese conditions to prevent any ow assurance related issues ta(ing place during s"ut down or warm up. /ome times to maintain desired conditions during s"utdown and warm warm up$ eter eternal nal interf interfer erenc ences es suc" suc" as "eatin "eating g of ow line$ line$ in"ibi in"ibitor tor in*ection are applied.

6. ,plain in detail about t"e di&erent design parameters to be considered during t"e development of a subsea eld layout? Ans: Following design parameters are to be considered during development of  subsea eld layout 7 8umber and si5e of ow lines$ w"ic" depends on t"e reservoir capacity 7 #igging: round trip or subsea pig launc"er Flowing ell"ead #ressure 7 9aterial /election 7 Corrosion Control #"ilosop"y 7 all !"ic(ness 7!"ermal +nsulation 7 Cat"odic #rotection 7 /pan Corrections  #ipeline Crossings 7 +nstallation 9et"od  )esign 7 Flowline Connections 7 ;iser Conguration •

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)escribe t"e pros and cons of single ow line and dual ow lines for a subsea tiebac( system. Ans: /ubsea tiebac( system "aving single ow line "ave di=culty in implementing pigging facility. For pigging$ t"ey need subsea piglaunc"er or subsea pig receiver$ w"ic" can communicate pig to and from topside end of  ow line. 4ut if t"ere are dual ow lines$ it facilitates round pigging across ow line. !"is means t"at pig can be launc"ed and received on t"e topside end of ow line. !"is eliminates re%uirement of subsea pig launc"erreceiver and simplies t"e tiebac( system. >. ,plain t"e di&erence between F#/s and Fied @ac(et #latform for "ost processing facilities. Ans: F#/ is abbreviation for oating production storage and ooading vessel. +t is a oating vessel w"ic" maintains its location by dynamic positioning to cope up wit" waves and currents and t"us providing virtually stable topside facility to subsea systems. n t"e ot"er "and$ ed *ac(et platform are mobile platforms$ w"ose legs can be ed on seabed. "en t"eir wor( is done at a place$ t"ose legs can be retrieved from seabed and t"e w"ole structure can be moved to anot"er place and anc"ored in similar way. !"e ed *ac(et platform$ once ed$ do not re%uired continuous dynamic positioning. !"e anc"ored legs are su=cient to "old t"e platform at a place.

Fied *ac(et platform are used for relatively s"allow water 211BB m3$ w"ile F#/ is used for ultra deep water 2-6BB m3. . ,plain t"e @oule!"ompson e&ect w"en restarting well production from cold conditions. )escribe t"e (ey tec"nical issues wit" t"is p"enomenon and suggest possible tec"ni%ues to mitigate. Ans: "ile restarting well production from cold condition$ w"en uid passes t"roug" c"o(es it epands and its pressure decreases due to @oule!"ompson e&ect. !"e uid goes into "ydrate formation 5one due to t"is e&ect. #ossible tec"ni%ue to mitigate t"is p"enomenon is to circulate warm oil t"roug" ow line to (eep t"e temperature of pipeline above "ydrate formation temperature. D.

)escribe common design met"ods to manage "ydrate formation in subsea systems. Ans: 9ainly two tec"ni%ues are used to manage "ydrate formation 1. Eeeping t"e temperature of ow above "ydrate formation temperature:  !"is can be ac"ieved by providing insulation around ow line$ )irect electrical "eating of ow lines$ or circulation of warm ow around ow line. -. /econd met"od is in*ecting c"emical in"ibitors in t"e "ydrocarbon uids.  !"ese in"ibitors$ due to t"eir c"emical c"aracteristics$ w"en mied wit" t"e "ydrocarbon$ bring t"e "ydrate formation temperature out of t"e operating temperature range. !"us$ (eeping t"e "ydrocarbon uid out of  t"e "ydrate formation 5one.

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,plain di&erent tec"nical c"allenges considered in a typical subsea eld development. Ans: 'arious tec"nical c"allenges considered in a typical subsea eld development are as following. )eeper water dept"s 0 deeper water dept" means di=cult installation$ di=cult drilling and comple system for production and storage 7 Gonger o&sets tiebac(s w"ic" means longer *umper distance$ more ependiture on ow lines and comple design of ow lines. 74at"ymetry sometimes$ di=cult terrain of sea bed introduces design and installation c"allenges for subsea ow lines 7 Arctic environment etreme temperature conditions and eistence of ice on t"e sea surface ma(es it di=cult installation of subsea system components 7 Gowenergy reservoirsrecovery from low energy reservoir is a di&erent c"allenge all toget"er 7 Heavy oil •

7 /ubsea commingling +t means bringing number of wells toget"er subsea using manifolds and etracting t"e product at t"e topside from t"em using a single ow line. !"e c"allenges faced are di&erent %uality and c"aracteristics of "ydrocarbon from di&erent wells$ and designing system components based upon t"at. 7 9arginal and smaller elds 0 many times it is di=cult to *ustify large capital investment for marginal and smaller elds because of t"e epected low return from t"em. 7 /ubsea processing suc" as separation$ compression etc. are relatively new concepts presents tec"nological c"allenges. .

)escribe general outline of a ow line design using #+#,/+9 software. Ans: First step to ow line design is to input data. Following data are given as input to t"e software. !"is input data "as information about nature of  ow2single p"asemultip"ase3$ uid model$ bubble point pressure and temperature$ viscosity correlation$ I;$ water cut$ production rate$ sea bed temperature$ water dept"$ reservoir dept"$ reservoir temperature$ reservoir pressure$ productivity inde$ separator pressure$ riser lengt"$ Flowline lengt"$ Flowlineriser "eat coe=cient value$ Flowlineriserproduction tubing wall t"ic(ness$ Flowlineriser roug"ness$ sand content etc. +t is wort" mentioning t"at some of t"e above mentioned values can be given as input to t"e pipesim or pipesim "as t"e ability to calculate t"em and sometimes$ it ta(es default value based on some models already present in t"e software database. 4ased on t"e input data$ pipesim prepares layout model for t"e w"ole system$ w"ic" contains di&erent components suc" as well "ead$ Flowline$ riser and topside separator. 4ased on t"e given input$ pipesim performs analysis and gives result t"at displays various ow c"aracteristics prole in t"e system as well as c"anges in t"em wit" time as well. /everal w"atif analysis can also be performed from t"e results. /ome eamples of output results generated by pipesim are given below. #ressure and temperature prole along t"e Flowline and riser ,&ect of water cut on pressure and temperature drop Gi%uid and gas "old up along t"e Flowline and riser Flow regime ,rosion estimation$ depends on uid velocity and solid particles in t"e "ydrocarbon$ ma(es use of already establis"ed eperimental models Fluid density. 9ost of t"ese results are presented in t"e prole form along t"e system$ w"ic" ma(es it easier to understand overall be"avior and identify t"e critical points in t"e system. • • • • •

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1B.How is #'! analysis done in ow assurance lab? Ans: +n a #'! lab$ t"e researc"ers use variety of instruments to determine reservoir uid properties from t"e samples obtained from eld. !"eir ob*ective is to simulate w"at "appens in t"e reservoir and at t"e surface during actual production. 9ain focus of pvt analysis is to determine "ow gas evolves from oil w"en pressure in t"e reservoir falls below t"e bubble point. !wo processes are used to describe t"is 0 as" liberation and di&erential liberation. +n as" liberation $ gas comes out of t"e oil as t"e pressure is gradually decreased and remains conned wit" t"e oil. "ile in t"e di&erential liberation $ gas is removed from oil. "en reservoir pressure drops below t"e bubble point pressure $ as" liberation dominates. 4ut$ w"en enoug" gas is accumulated in t"e reservoir $ it begins to ow$ since gas is less viscous and ows faster t"an oil$ di&erential liberation occurs. Flas" and di&erential liberation are recreated in lab using "ig" pressure "ig" temperature pvt cells$ positive displacement mercury pump and "ig" accuracy pressure and temperature gauges. Flas" liberation test is used to determine bubble point temperature of reservoir uid. 4ot" as and di&erential liberation are utili5ed to determine parameters t"at relate surface volume of "ydrocarbons to t"at of t"eir volume in reservoir. /uccessful #'! analysis re%uires t"at sample represents t"e original uid in t"e reservoir. !"erefore$ sample must be obtained soon after eploration wells are drilled.