SPREAD MOORINGSYSTEMS

ROTARY DRILLING

Second EditionUNIT V • LESSON 2

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rotary drilling series

Unit i: the rig and its Maintenance

Lesson1: TheRotaryRigandItsComponentsLesson2: TheBitLesson3: DrillStringandDrillCollarsLesson4: Rotary,Kelly,Swivel,Tongs,andTopDriveLesson5: TheBlocksandDrillingLineLesson6: TheDrawworksandtheCompoundLesson7: DrillingFluids,MudPumps,andConditioningEquipmentLesson8: DieselEnginesandElectricPowerLesson9: TheAuxiliariesLesson10: SafetyontheRig

Unit ii: normal drilling operations

Lesson1: MakingHoleLesson2: DrillingFluidsLesson3: DrillingaStraightHoleLesson4: CasingandCementingLesson5: TestingandCompleting

Unit iii: nonroutine operations

Lesson1: ControlledDirectionalDrillingLesson2: Open-HoleFishingLesson3: BlowoutPrevention

Unit iV: Man Management and rig Management

Unit V: offshore technology

Lesson1: Wind,Waves,andWeatherLesson2: SpreadMooringSystemsLesson3: Buoyancy,Stability,andTrimLesson4: JackingSystemsandRigMovingProceduresLesson5: DivingandEquipmentLesson6: VesselInspectionandMaintenanceLesson7: HelicopterSafetyLesson8: OrientationforOffshoreCraneOperationsLesson9: LifeOffshoreLesson10: MarineRiserSystemsandSubseaBlowoutPreventers

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contentsFigures v

Foreword ix

Preface xi

Acknowledgments xiii

UnitsofMeasurement xiv

HoldingFloatingVessels 1 Early Mooring Systems 1Offshore Environments 9Mooring Patterns 11Principles of Mooring Systems 12

Anchor Holding Power 12Catenary Curves 14

To summarize 19

ComponentsofMooringSystems 21Mooring Line Arrangements 21

Types of Anchors 23Stud-Link Chain 30Wire Rope 35

Connecting Elements 41Chain Fittings 42Wire Rope Fittings 44

Storing the Rope 46Types of Winches 47

Pulling In and Running Out Chain 50Windlass Components 51

Measuring Mooring Line Tension 53Chain Tension Measurements 53Wire Rope Tension Measurements 56

Pulling and Lowering Anchors 57Anchor-Handling Boats 59To summarize 62

PlacingandRecoveringMoorings 63Planning a Successful Mooring Operation 63Moving Onto Location 65

Running Out an Anchor 66Setting an Anchor 68Preloading and Pretensioning Anchor Lines 69Piggybacking Anchors 69

Adjusting Mooring Systems in Rough Weather 70Pulling an Anchor 70

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Moving Off Location 73To summarize 78

References 79

Appendix 81

Glossary 87

ReviewQuestions 91

Index 95

Answers 101

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Preface

The use of dynamically posi-tioned vessels has certainly

increased dramatically in recent years, but spread moorings still play a vital role in the offshore drill-ing industry. Innovations in mooring line materials, anchor holding power, and deployment and retrieval methods have improved the efficiency of mooring systems since the original text of this book was written over thirty years ago.

While the subject of spread mooring systems and equipment is necessarily quite complex, this updated text attempts to explain the main principles and applications to participants of the drilling industry in an understandable way. It is intended to give readers a basic overview of the topic from a historical and an operational viewpoint, while touching on the technical details in sufficent depth to understand their importance and relevance.

christopher Morlan Manaer of Structural engineering and naval architectureMoU engineering at SBM atlantia in Houston, texas

Morlan, who contributed his significant expertise to enhancing this new edition of Spread Mooring Systems, has several years of experience review-ing and analyzing floating offshore structures including semisubmersibles, jackups, drillships, barges, and various small vessels. His background also includes experience with drilling rig layout, design, weight control, and vessel interface; and extensive experience in stability analysis, motions response analysis, mooring analysis, riser analysis, and design and weight management. He has conducted inclining experiments and deadweight surveys on jackups, semisubmersibles, and drillships.

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Throughout the world, two systems of measurement domi-nate: the English system and the met ric system. To day, the

United States is one of only a few countries that employs the En-glish sys tem.

The English system uses the pound as the unit of weight, the foot as the unit of length, and the gallon as the unit of capacity. In the En glish system, for example, 1 foot equals 12 inches, 1 yard equals 36 inches, and 1 mile equals 5,280 feet or 1,760 yards.

The metric system uses the gram as the unit of weight, the metre as the unit of length, and the litre as the unit of capacity. In the metric system, 1 me tre equals 10 decimetres, 100 centime-tres, or 1,000 milli metres. A kilometre equals 1,000 me tres. The metric system, un like the English system, uses a base of 10; thus, it is easy to convert from one unit to another. To convert from one unit to an other in the English system, you must memorize or look up the val ues.

In the late 1970s, the Eleventh General Conference on Weights and Measures de scribed and adopted the Système International (SI) d’U nités. Conference participants based the SI system on the metric system and de signed it as an interna tional stan dard of measurement.

The Rotary Drilling Series gives both English and SI units. And because the SI sys tem employs the British spelling of many of the terms, the book follows those spelling rules as well. The unit of length, for ex ample, is metre, not me ter. (Note, however, that the unit of weight is gram, not gramme.)

To aid U.S. readers in making and understanding conversion to the SI system, we in clude the following table.

Units of Measurement▼▼▼

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Quantity Multiply to obtain or Property english Units english Units By these Si Units Length, inches (in.) 25.4 millimetres (mm) depth, 2.54 centimetres (cm) or height feet (ft) 0.3048 metres (m) yards (yd) 0.9144 metres (m) miles (mi) 1609.344 metres (m) 1.61 kilometres (km) Hole and pipe di ame ters, bit size inches (in.) 25.4 millimetres (mm) Drilling rate feet per hour (ft/h) 0.3048 metres per hour (m/h) Weight on bit pounds (lb) 0.445 decanewtons (dN) Nozzle size 32nds of an inch 0.8 millimetres (mm) barrels (bbl) 0.159 cubic metres (m3) 159 litres (L) gallons per stroke (gal/stroke) 0.00379 cubic metres per stroke (m3/stroke) ounces (oz) 29.57 millilitres (mL) Volume cubic inches (in.3) 16.387 cubic centimetres (cm3) cubic feet (ft3) 28.3169 litres (L) 0.0283 cubic metres (m3) quarts (qt) 0.9464 litres (L) gallons (gal) 3.7854 litres (L) gallons (gal) 0.00379 cubic metres (m3) pounds per barrel (lb/bbl) 2.895 kilograms per cubic metre (kg/m3) barrels per ton (bbl/tn) 0.175 cubic metres per tonne (m3/t)

gallons per minute (gpm) 0.00379 cubic metres per minute (m3/min) Pump output gallons per hour (gph) 0.00379 cubic metres per hour (m3/h) and flow rate barrels per stroke (bbl/stroke) 0.159 cubic metres per stroke (m3/stroke) barrels per minute (bbl/min) 0.159 cubic metres per minute (m3/min)

Pressure pounds per square inch (psi) 6.895 kilopascals (kPa) 0.006895 megapascals (MPa)

Temperature degrees Fahrenheit (°F) degrees Celsius (°C)

Thermal gradient 1°F per 60 feet –– 1°C per 33 metres ounces (oz) 28.35 grams (g) Mass (weight) pounds (lb) 453.59 grams (g) 0.4536 kilograms (kg) tons (tn) 0.9072 tonnes (t) pounds per foot (lb/ft) 1.488 kilograms per metre (kg/m) Mud weight pounds per gallon (ppg) 119.82 kilograms per cubic me tre (kg/m3) pounds per cubic foot (lb/ft3) 16.0 kilograms per cubic me tre (kg/m3) Pressure gradient pounds per square inch per foot (psi/ft) 22.621 kilopascals per metre (kPa/m) Funnel viscosity seconds per quart (s/qt) 1.057 seconds per litre (s/L) Yield point pounds per 100 square feet (lb/100 ft2) 0.48 pascals (Pa) Gel strength pounds per 100 square feet (lb/100 ft2) 0.48 pascals (Pa) Filter cake thickness 32nds of an inch 0.8 millimetres (mm) Power horsepower (hp) 0.75 kilowatts (kW)

square inches (in.2) 6.45 square centimetres (cm2) square feet (ft2) 0.0929 square metres (m2) Area square yards (yd2) 0.8361 square metres (m2) square miles (mi2) 2.59 square kilometres (km2) acre (ac) 0.40 hectare (ha) Drilling line wear ton-miles (tn•mi) 14.317 megajoules (MJ) 1.459 tonne-kilometres (t•km) Torque foot-pounds (ft•lb) 1.3558 newton metres (N•m)

°F - 32 1.8

english-Units-to-Si-Units conversion Factors

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Mooring system. Surface and underwater views of a typical spread mooring system in offshore operations

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HoldingFloatingVessels

In this chapter:

• Anchorsandmooringlinesusedforoffshoreoperations

• Typicalmooringsystempatterns

• Principlesofanchorandmooringlinebehavior

• Balancingandcounterbalancinghorizontalforces

Holdingafloatingvesselnearafixedlocationonthesurfaceofthesea,calledmooring,isanage-oldchallenge.Basicprinciplesand

conceptshavechangedlittlesinceancienttimes;however,technologiesandapplicationshaveimprovedmarkedly.Asoilandgasexplorationhasmovedincreasinglyoffshore,morepermanentmooringsystemshavebeendevelopedtokeepfloatingoperationsinplace.

Theearliestmooringsystemsconsistedofnaturalfiberropesattachedtoanchorstones.Varioustypesofanchorstones,datingbackasfaras1600B.C.,havebeenrecoveredfromEgyptiantombsandtheMedi-terraneanSeafloor.Metalanchorswereintroducedbytheyear800B.C.,whenbronzeanchorswerecastontheislandofMalta.By300B.C.,ironanchorswerecommontoshipsoftheAtheniannavy.Asshowninfigure1,someoftheseearlyanchorscontainthefeaturesofrelativelymodernanchors.RapiddevelopmentofanchorsintheyearsfollowingtheIndustrialRevolutionculminatedinthestockless anchoroftheearlytwentiethcentury.

EarlyMooringSystems

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ComponentsofMooringSystems

In this chapter:

• Mooringlinearrangements

• Typesofanchors

• Wirerope,chain,connectors,andfittings

• Anchor-handlingequipment

• Tensionmeasurement

Figures17and18showtwomooringlinearrangementsthatareused.One is a chainconfigurationcommonlyused in shallow

water; theother is a compositewire ropeandchainconfigurationcommonlyusedindeeperwater.Botharrangementscontainprac-tically all components found in spreadmooring systems: anchors,wirerope,chain,endfittings,buoys,andhandlingequipmentsuchaswinchesandwindlasses.Notshownareanchor-handlingboatsthatdeployandretrievetheanchors.

Maincomponentsofaspreadmooringsystem:

• Buoystomarklocations

• Anchorstodropweighttoholdavessel

• Wireropeandchaintomakeupthemooringline

• Endfittingstoaddholdingpower

• Winchestohandleandstorerope

• Windlassestopropeltheline

MooringLineArrangements

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In this chapter:

• Companiesinvolvedinmooringoperations

• Movingonandofflocation

• Runningandsettingmooringpatterns

• Pullingupanchors

• Functionofanchor-handlingboats

Asuccessful mooring operation requires considerable planningandorganization.Thewellsiteshouldbemarkedandsurveyedandthebottomconditionsestablishedbeforetherigmovesontoloca-tion.Whenwaterdepthsareknown,pendantlinescanbecheckedforcorrectlengths.Itisimportanttoinventoryandinspectallmooringcomponents and handling equipment to ensure they are availableand in good condition. Anymissing or damaged items should bereplacedorrepaired.Allparticipatingpersonnelshouldreviewandunderstandallequipmentandprocedurestoensuresafeandefficientoperations(fig.61).

Constantandclosecoordinationbetweenthedrillingrigandtheanchor-handlingboatisessentialduringthemooringoperation.Clearlinesofcommunicationshouldbeestablishedbeforehandtoavoidanyconfusiononthejob.Thistaskiscomplicatedbythefactthatmultiplecompanies,organizations,and individualsmightbeinvolved.

PlacingandRecoveringMoorings

PlanningaSuccessfulMooringOperation

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INDEX

Index

airtuggers,61

AmericanBureauofShipping,30

anchorbehaviordependentonbottomconditions,13

anchorchainmooringlineandrelated equipment,22

anchorchains

oilrigtowingwith,76

pulledoffanchor,75

swivelfairleadfor,55

anchor-handlingboats,21,59–62

heaveof,71

settinganchorfrom,68

anchor-handlingdeckequipmentarrangement,61

anchor-handlingoperation,76

anchor-handlingoperator,64

anchor-handlingvesseladjacenttooffshorerig,60

anchor-handlingwinch,38,48

anchorholdingpower,12–14

anchors anchorchainpulledoff,75

basic-type,withidentifiedparts,13

ofhistoricalinterest,2

mooringpatternand,65

orderofretrieving,73

sequenceofsettingandretrieving,65

typesof,23–29

API Specification for Mooring Chain (APISpec.2F),(AmericanPetroleumInstitute),34

Baldtdetachableanchorconnectinglink,42

Baldtdetachablechainconnectinglink,42

Baldtswivelsandendshackles,43

ballingup,12

ball-jointends,10

blowoutpreventer(BOP)stack,9

blowouts,47,51

BOSSanchor,25

breaking-strength,3

Bruce®anchor,26

buoys

beingtransportedforoffshoreoperations,58

ondeck,59

catenarycurves,3,14–19

chainandwildcat,checkingfitbetween,52

chainlinetensionmeasurement,53,54

chainlocker,50,51

chainmooringlines,22

andwireropecombination,18,22

chains.See alsoanchorchains cracksin,34

crownchain,57

Di-Lokchain,30,31,32

fatiguein,34

flash-buttweldedchain,33

mooringchain,50

mooringlines,18,22

OilRigQuality(ORQ),30

specificationfor,30,34

stud-linkchain,30–34Petr

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chainspecifications,30,34

chainstoppers,51

chainsystemsfailurepoints,41

chaintension,maximum,30

chaintensionmeasurements,53–54

chasers,70

chaserwire,73

lockedin,74

andworkwire,74

chock,53

combinationwireropeandanchorchainmooringline,22

combinationwireropeandchainmooringline,18

compositelines,22

compositemooringlines,18

connectingelements,41–42

fatiguefailuresof,41

controllablepitchpropellers,59

conversionfactors,EnglishunitstoSIunits,xv

cracksinchains,34

crownchain,57

Danforth®anchor,23

deckequipmentarrangementforanchorhandling,61

DeltaAnchor™,26

Di-Lokchain,30

dimensionsandtestrequirements,32

Di-Lokstud-linkchainmanufacturingprocess,31

drillingoperator,64

drillingtenders,4,6

drillshiparrangementofmooringlinesanddrillingassembly,7

drillships,6,7

dual-drumwinches,46

dynamicpositioningsystemcontrols,8

dynamicpositioningsystems,8

eight-linespreadmooringpattern,5

eight-linespreadmooringsystem,5

emergencyreleasesystems,47

emergencysituations,51

environmentalforceappliedtoasemisubmersible,17

ExtraExtraImprovedPlowSteel(EEIPS),41

ExtraImprovedPlowSteel(EIPS),41

extremeweather,71

failures,41

chainsystems,41

wireropesystems,41

fairlead,15

fairleadblockandstopperline,55

fatiguedamageofmooringlines,23

fatiguefailuresofconnectingelements,41

fatigueinchains,34

flash-buttweldedchain,33

flash-buttwelding,30

flexuralstrength,15

floatingdrillingvessels,23

floatingvessels,1–19

mooringpatterns,11

mooringsystems,early,1–8

offshoreenvironments,9–11

principlesofmooringsystems,12–19

flukeangle,23,26

flukeangleblocks,28

flukeanglesetting,14

forerunner,26

globalpositioningsystem(GPS),65

handlingloads,62

heavecompensators,9,10

heavingin,68

HighHoldingPower(HHP)anchor,26Petr

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horizontalmooringlineforce,16

ImprovedPlowSteel(IPS),41

independentwireropecore(IWRC),40

Kenterconnectinglink,42

Kortnozzles,59

LandingShipTanks(LSTs),5

langlayrope,40

lay,40

leeward(downwind)lines,16

leftlay,40

linkofastud-linkanchorchain,30

loadcell,53,54,56

loadsandenvironmentalforcesonasemisubmersibledrillingrig,6

maximumallowableload,16

maximumhorizontalresistingforce,18

measuringmooringlinetension,53–56

chaintensionmeasurements,53–55

wireropetensionmeasurements,56

Moorfastanchor,24

mooring,1

mooringbuoys,58

mooringchain,50

mooringequipmentonthebowsection,47

mooringlinearrangements,21–45,62

connectingelements,41–42

stud-linkchain,30–34

typesofanchors,23–29

wirerope,35–41

wireropefittings,44–45

mooringlines,1,3,5-7,9,11-12,14-15,18, 21-22,30-41

fatiguedamageof,23

sizeclassification,38

mooringlinetension,15

parametersrequiredtocalculate,15

mooringpatterns,5,11

andsequenceofsettingandretrieving anchors,65

mooringsystemprinciples,12-19

anchorholdingpower,12–14

catenarycurves,14–19

mooringsystems

anchor-handlingboats,59–62

componentsof,21–62

early,1–8

measuringmooringlinetension,53–56

mooringlinearrangements,21–45

principlesof,12–19

pullingandloweringanchors,57–58

roughweatheradjustment,70

storingtherope,46–49

windlasses,50–52

movingofflocation,73–74

movingontolocation,65–70

adjustingmooringsystemsinrough weather,70

piggybackinganchors,69–70

preloadingandpretensioninganchor lines,69

pullingananchor,70–72

runningoutananchor,66–67

settingananchor,68

naturalfiberrope,3

OffdrillIIanchor,24,25

offshoreenvironments,9–11

OilRigchain,30

OilRigQuality(ORQ),30

oilrigtowing,77

withanchorchains,76Petr

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operator,64

payout,65

payoutrate,67

pelicanhooks,70

pelicanhook-typechainstopper,42,43

pendantlines,57

attachmentlocationsfor,65

lengthof,70

springbuoyholding,57

wireropefor,38

piggybacking,69

piggybackinganchors,69–70

pile-typeanchors,28,29

placingandrecoveringmoorings,63–74

movingofflocation,73–77

movingontolocation,65–70

planningasuccessfulmooringoperation,63–64

polyesterrope,19

preloading,69

preloadingandpretensioninganchorlines,69

proofload,30

propwash,58

pullingananchor,70–72

pullingandloweringanchors,57–58

pullinginandrunningoutchain,50

pullpershafthorsepower,59

quadruple-drumwinches,46

Recommended Practice for Design and Analysis of Stationkeeping Systems for Floating Structures(RP-2SK)(AmericanPetroleumInstitute),34

regularlay,40

restoringforcesforasemisubmersibleduetohorizontaldisplacementfromthewell,17

rightlay,40

ropelay,40

roughweatheradjustingmooringsystemsin,70

runninganchor,sequenceof,65

runningoutananchor,66–67

scope,14

Sealeconstruction,38

semisubmersibles,7

settinganchor,68

fromanchor-handlingboat,68

shafthorsepower,59

sheavediameters,41

single-drumwinches,46

single-flukedesign,25

slipjoints,9

socketfittings,44

spreadmooringpatterns,11

spreadmooringsystemscomponents,21

springbuoy,57

springbuoyholdingpendantline,57

STATOanchor,24

StevmantaVLA™(VerticallyLoaded Anchor),28

Stevpris™anchor,26,72,75

StevprisMk6™anchor,27,28

Stevshark™anchor,26,27

stocklessanchor,1

stopperlineandfairleadblock,55

stoppers,42

storingtherope,46–49

stormconditions,70

stormtensions,70

stud,30

stud-linkchain,30–34

submersiblebarges,6

suctionpile,29

surveyboat,65

surveycompany,64

swagedsockets,44

swivelfairlead,54-55

foranchorchain,55

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INDEX

swivels,42

tailroller,61

tension

chaintension,maximum,30

chaintensionmeasurements,53–55

measuringmooringlinetension,53–56

mooringlinetension,15

parametersrequiredtocalculate,15

preloadingandpretensioninganchor lines,69

stormtensions,70

three-sheavewirelinetension-measuring device,56

wirelinetension-measuringdevice,three-sheave,56

wireropetensionmeasurements,56

thimbles,45

thrusters,8

traction-winchtype,49

trips,12

turretmooring,8

turret-typemooringarrangement,9

Ulsterpawl-typestopper,42,43

U.S.NavyLightweight(LWT)anchor,23

verticalcenterofgravity(VCG),35

Warringtonconstruction,38

waterdepths,22

watertightcompartments,60

wellheadflexibleconnection,connector,andblowoutpreventerarrangement,10

whelps,51

wildcats,51

winchdrum,49

winches,21

anchorhandling,38,48

typesof,46–49

windlasscomponents,51–52

windlasses,21

pullinginandrunningoutchain,50

windlasscomponents,51–52

windlasswildcatandchain-handling equipment,51

windward(upwind)lines,16

wirelinetension-measuringdevice,three-sheave,56

wirerope,3,35–41

6x19classification,galvanized, independentwireropecore,38

6x37classification,bright(uncoated)or drawngalvanizedwire,independent wireropecore,39

advantagesanddisadvantagesof,35

andchainmooringlinecombination,18,22

classificationsof,37

constructionof,36

constructiontypes,38

forpendantlines,38

precautionswith,40

wireropecore,38

wireropefabricationterminology,36

wireropefibercore,40

wireropefittings,43–45

wireropelubricants,40

wireropesystemfailurepoints,41

wireropetensionmeasurements,56

wireropethimble,45

wireropewindingprocedures,49

wirestrandcore(WSC),40

workwireandchaserwire,74

zinc-pouredsockets,44Petrole

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To obtain additional training materials, contact:

PETEXThe University of Texas at Austin

Petroleum extension service10100 Burnet Road, Bldg. 2

Austin, TX 78758

Telephone: 512-471-5940or 800-687-4132

FAX: 512-471-9410or 800-687-7839

E-mail: petex@www.utexas.eduor visit our Web site: www.utexas.edu/ce/petex

To obtain information about training courses, contact:

PETEXlearning and assessment center

The University of Texas4702 N. Sam Houston Parkway West, Suite 800

Houston, TX 77086

Telephone: 281-397-2440or 800-687-7052

FAX: 281-397-2441E-mail: plach@www.utexas.edu

or visit our Web site: www.utexas.edu/ce/petex

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2.502200-88698-253-7

978-0-88698-253-9

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