Surface production operations. Volume 2, Design of gas-handling systems and facilities PDF
Preview Surface production operations. Volume 2, Design of gas-handling systems and facilities
VOLUMETWO SURFACE PRODUCTION OPERATIONS VOLUMETWO SURFACE PRODUCTION OPERATIONS Design of Gas-Handling Systems and Facilities 3rd Edition MAURICE I. STEWART, Jr. PhD, PE Principal, Stewart Training and Consulting LLC, McLean, Virginia, USA AMSTERDAM (cid:129) BOSTON (cid:129) HEIDELBERG (cid:129) LONDON NEW YORK (cid:129) OXFORD (cid:129) PARIS (cid:129) SAN DIEGO SAN FRANCISCO (cid:129) SYDNEY (cid:129) TOKYO Gulf Professional Publishing is an imprint of Elsevier GulfProfessionalPublishing: GulfProfessionalPublishingisanimprintofElsevier 225WymanStreet,Waltham,MA02451,USA TheBoulevard,LangfordLane,Kidlington,Oxford,OX51GB,UK Copyright©2014,1999,1989,ElsevierInc.Allrightsreserved. Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans, electronicormechanical,includingphotocopying,recording,oranyinformationstorageand retrievalsystem,withoutpermissioninwritingfromthepublisher.Detailsonhowtoseek permission,furtherinformationaboutthePublisher’spermissionspoliciesandour arrangementswithorganizationssuchastheCopyrightClearanceCenterandtheCopyright LicensingAgency,canbefoundatourwebsite:www.elsevier.com/permissions. Thisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightby thePublisher(otherthanasmaybenotedherein). Notices Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchand experiencebroadenourunderstanding,changesinresearchmethods,professionalpractices, ormedicaltreatmentmaybecomenecessary. Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgein evaluatingandusinganyinformation,methods,compounds,orexperimentsdescribed herein.Inusingsuchinformationormethodstheyshouldbemindfuloftheirownsafetyand thesafetyofothers,includingpartiesforwhomtheyhaveaprofessionalresponsibility. Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors, assumeanyliabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterof productsliability,negligenceorotherwise,orfromanyuseoroperationofanymethods, products,instructions,orideascontainedinthematerialherein. LibraryofCongressControlNumber AcataloguerecordforthisbookisavailablefromtheLibraryofCongress BritishLibraryCataloguing-in-PublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary ISBN:978-0-12-382207-9 ForinformationonallGulfProfessionalpublications visitourwebsiteatstore.elsevier.com ThisbookhasbeenmanufacturedusingPrintOnDemandtechnology.Eachcopyis producedtoorderandislimitedtoblackink. PREFACE As teachers of surface production facility design in petroleum engineering programs at Louisiana State University and the University of Houston, KenandIrealizedthatnosinglesourcecouldbeusedasatextinthisfield. We found ourselves reproducing pages from catalogs, reports, and projects wehaddonetoprovideourstudentswiththebasicinformationtheyneeded to understand our lectures and carry out their assignments. More impor- tantly, the material that did exist usually contained nomographs, charts, and rules of thumb that did not refer to the basic theories and underlying assumptionsuponwhichtheywerebased.AlthoughVolume2oftenbuilds uponinformationthatwaspresentedinSurfaceProductionOperations,Vol- ume 1: Design of Oil-Handling Systems and Facilities, it does present the basic concepts and techniques necessary to select, specify, and size gas- handling, conditioning, and processing equipment. After the initial release ofthefirsttwovolumes,werealizedthatmanytopicsneededtobecovered inmoredepth.Asaresult,threeadditionalvolumeswereaddedtotheseries, tobepublishedatalatertime.Volume3coversthedesignoffacilitypiping and pipeline systems, as well as relief and vent disposal systems; Volume 4 covers rotating equipment, specifically pumps, compressors, and drivers; andVolume5coversinstrumentation,processcontrol,safetysystems,elec- trical installations in hazardous (classified) locations, and project and risk management. Volume 2, which covers one semester’s work or a two-week short course,focusesontheprocessesandequipmentinvolvedwithgas-handling, conditioning,andprocessingfacilities.Theobjectiveofgas-handling,con- ditioning, and processing facilities is to separate natural gas, condensate, or oilandwaterfromagas-producingwellandconditionthesefluidsforsaleor disposal.Specificareasaddressedbythisvolumeincludebasicprinciplesand fluid properties, process selection, heat transfer and heat exchanger equip- ment, hydrate prediction and prevention, condensate stabilization, com- pression, dehydration, acid gas treating, and gas processing. As was the case with Volume 1, this text covers topics that are common to both oil- and gas-handling production facilities, such as surface safety systems. Throughoutthetextwehaveattemptedtoconcentrateonwhatweper- ceive to be modern and common practices. We have personally been involved in the design and troubleshooting of such modern facilities ix x Preface throughout the world, or we have people in our organizations who have doneso.Undoubtedly,weareinfluencedbyourownexperienceandprej- udices. We apologize if we left something out or have expressed opinions about equipment types that differ from your own. We have learned much from our students’ comments about such matters and would appreciate receiving your input for future revisions/editions. Maurice I. Stewart, Jr. PhD, PE McLean, Virginia, USA ACKNOWLEDGMENTS IwouldliketothankKenArnoldforhisinsight,knowledge,andguidance in the preparation of Surface Production Operations, Volume 1: Design of Oil-HandlingFacilitiesandVolume2:DesignofGas-HandlingFacilities. WithoutKen’sexpertcontributions,Volumes1and2wouldnothavebeen possible.KenandIarealsoindebtedtothemanycompaniesandindividuals who,overthepast30years,haveaidedusbyprovidinghoursofargument andinsightaboutthevarioustopicscoveredinthesevolumes.Withouttheir help,Volumes1and2wouldnothavebeenpossible.Iofferafinalthankyou toHeriWibowoforhisdraftingandcoordinatingefforts,aswellastheabil- ities he showed in putting everything together for the third edition of Volume 2. xi CHAPTER ONE Overview of Gas-Handling, Conditioning, and Processing Facilities Volume 1 of the Surface Production Operations series focuses on the pro- cesses and equipment involved with oil-handling facilities. Volume 2 focusesontheprocessesandequipmentinvolvedwithgas-handling,condi- tioning, and processing of natural gas for sale. Volume 3 focuses on plant (facilities)pipingandpipelinesystems.Italsocoversrelief,ventandflaresys- tems. Volume 4 focuses of rotating equipment, specifically pumps, com- pressors and drivers. Volume 5 focuses on instrumentation, process control and safety systems. The objective of gas-handling, conditioning, and processing facilities is to separate natural gas, condensate, or oil and water from a gas-producing well and condition these fluids for sale or disposal. Chapter 2 discusses basic principles and fluid properties. Heat transfer theory and heat exchanger equipment are discussed in Chapters 3 and 4. HydratepredictionandpreventionarediscussedinChapter5.Condensate stabilization,theprocessofflashingthelighterhydrocarbonstogasandmax- imizingtherecoveryofnaturalgasliquids(NGLs),isthetopicofChapter6. The subject of Chapter 7is methods of gas dehydration, and specific com- ments on maintenance, care, and troubleshooting of glycol dehydration systems are the topics of Chapter 8. Gas sweetening, the removal of acid gas compounds (primarily carbon dioxide and hydrogen sulfide) from nat- ural gas, is discussed in Chapter 10. Gas processing to extract natural gas components, primarily ethane, propane, butane and heavier NGLs, from a natural gas stream is discussed in Chapter 10. Treating the condensate, or oil and water, after the initial separation from the natural gas is covered in Volume 1. Figure 1.1 is a simple block diagram of a production facility that is pri- marily designed to handle gas wells. Each of the main blocks is described herein. SurfaceProductionOperations ©2014ElsevierInc. 1 http://dx.doi.org/10.1016/B978-0-12-382207-9.00001-9 Allrightsreserved. 2 SurfaceProductionOperations Gas Gas Gas Dehydration theating processing sales Wells Cooling H.P. Heating Compressor separation Stabilization Oil sales Oil & water handling Figure1.1 Gasfieldfacilityblockdiagram. 1.1 HEATING The well flow stream may require heating prior to initial separation. Gas wells are often high pressure (HP) with shut-in tubing pressure of 5000-15,000psig and flowing-tubing pressure (FTP) often exceeding 3000psig. This pressure must be reduced to the appropriate operating pressure of the surface facilities and pipelines. Achokeisinstalledtocontroltheflow.Whentheflowstreamischoked, gasexpands,temperaturedecreases,andliquidscondense.Ifthetemperature getslowenough,hydrateswillform.Hydratesarecrystallinesolidsmadeup ofhydrocarbonandwatermoleculesandforminthepresenceofhydrocar- bongasandliquidwaterattemperaturessignificantlyhigherthanthefreez- ingpointofwater.Hydratescanplugtheflow-line,choke,anddownstream equipmentandreducethecapacityofvesselsandpipelines.Therefore,flow fromhigh-pressuregaswellsmayhavetobeheatedtoatemperatureabove thehydrateformationtemperaturebeforeorimmediatelyafterthepressure drop from FTP to separator pressure, which occurs at the choke. Refer to Chapter5onHydratePredictionandPrevention,ofthisvolume,fora more complete discussion of hydrates. GasHandling,ConditioningandProcessingFacilities 3 1.2 SEPARATION TheHPseparatorprovidesalocationforliquidtosettleoutfromthe gas.Normally,iftheFTPishighenough,theseparatorpressureissethigher thanthesalesgaspipelinepressuresothatthegascangothroughtherequired cooling, treating, dehydration, and gas processing equipment, experience some pressure drop, and arrive at the required departing pipeline pressure. Typically,inagasfacility,thereisaninitialseparationataHP,enabling reservoirenergytomovethegasthroughtheprocesstosales.Itisveryrare thattheflowing-tubingpressureofagaswell,atleastinitially,islessthanthe gas sales pressure. With time, the flowing-tubing pressure may decline and compressionmaybeneededpriortofurtherhandlingofthegas.Theinitial separation is normally three-phase, as the separator size is dictated by gas capacity.Thatis,theseparatorwilltypicallybelargeenoughtoprovidesuf- ficient liquid retention time for three-phase separation if it is to be large enoughtoprovidesufficientgascapacity.Selectionandsizingofseparators are described in Volume 1. 1.3 COOLING Itisalsopossiblethatcoolingmaybenecessary.Iftheflowinggastem- perature is high, the temperature downstream of the choke may be high enough so that adding heat upstream of the HP separator is not required. Ifasubstantialamountofgasandliquidisbeingproduced,oriftheflowing tubing temperature is very hot (e.g., from a deep high-pressure, high- temperature gas well), the gas temperature leaving the HP separator could beabovethetemperaturethatcaneasilybehandledbythedownstreampro- cesses. There is a maximum practical temperature for inlet streams to acid- gas treating and dehydration equipment. Hot gas leaving the HP separator carries more water vapor and increases the load on the downstream dehy- dration systems, which results in a much more expensive system than if the gas were cooled first. In addition, hot inlet gas could severely limit the ratio of discharge pressure to suction pressure that could be obtained fromadownstreamcompressor.Thus,thegasmayhavetobecooledprior to compression, treating, and/or dehydration. Thecooleristypicallyanaerialcoolerorashell-and-tubeexchangerthat uses seawater or a contained cooling-water loop, which is cooled by 4 SurfaceProductionOperations (cid:1) seawaterorsomeotherwatersource.Idealgastemperaturesareinthe80 - (cid:1) (cid:1) 110 F (27-43 C) range. Insomefields,itmaybenecessarytoprovideheatduringtheearlylifeof the wells when flowing-tubing pressures are high and there is a high- temperaturedropacrossthechoke.Lateron,ifthewellsproducemoreliq- uid and the flowing-tubing pressure decreases, it may be necessary to cool thegas.Liquidsretainthereservoirheatbetterandhavelessofatemperature drop associated with a given pressure drop than does gas. 1.4 STABILIZATION Liquid from the initial separator is stabilized either by reducing the pressureandlettingthelightercomponentsflash(multistageflashseparation) orbydistillation,whichisacombinationofpressurereductionandheating (condensate stabilization). Most of the water will be removed during sepa- ration.Theresultingstablecondensatehasalowvaporpressuresoitcanbe storedintanksforshippingatatmosphericpressurebytruck,train,barge,or shipwithoutexcessive vaporventing.Often,there arevapor-pressurelim- itations that require liquid stabilization for pipeline shipments as well. Stabilizationofthehydrocarbonliquidmaximizestherecoveryofinter- mediatehydrocarboncomponents(C toC )fromtheliquidstream.Mul- 3 6 tistageflashstabilizationisdiscussedinVolume1.Condensatestabilizationis discussed in this volume in Chapter 6. Thewaterandcondensateremoved intheseparation/stabilization pro- cess must be separated, treated, and disposed of as described in Volume 1. 1.5 COMPRESSION Thelightercomponentsremovedinthestabilizationprocesswillbeat alowerpressurethantheHPgasstream.Thesecomponentsmustbecom- pressedtotheHPseparatorpressuresothattheycanberecombinedwiththe gas from the HP separator for further processing. Both reciprocating and centrifugal compressors are commonly used. In low-horsepower installa- tions, especially for compressing gas from stock tanks (vapor recovery), screw or vane type compressors are common. Pumps, compressors, and drivers are covered in Volume 4.
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