Offshore
Content
3de Bach NW
Samenvatting p. 1/23
Offshore
Organisations
UKOOA – United Kingdom Offshore Operators Association
• • • Representative organisation for UK offshore oil & gas industry Members = companies licensed by Government to explore for & produce oil & gas Forum to deal with common interests & problems
IOOA – Irish Offshore Operator’s Association
• • • • Umbrella organisation Represents oil & gas companies with operating interests in Ireland’s offshore industry Forum to work together in identifying & tackling issues (such as safety, environment, legislation & employment) Focal point for liaison between companies & industry itself
NAPE – Nigerian Association of Petroleum Explorationists
• • • • Non-profit organisation Objectives & membership governed by Bye-Laws Activities supported by corporate membership grants & donations Cause of educational development of students & professionals
NOGEPA – Netherlands Oil & Gas Exploration & Production Association
• • • • Promote common interests of all companies holding licences to explore for, develop & produce hydrocarbons on- & offshore in the Netherlands Provides means of communication with Government, media & other third parties Coordinates industry efforts to assume safety & health of people & protection of environment Main activities carried out in committees & workgroups
OGP – International Association of Oil & Gas Producers
• • • • • Encompasses world’s leading publicly traded, private & state-owned oil & gas associations More than half world’s oil & one third gas Develop effective communications between industry & international regulations Represents interests of industry before international regulators & legislators Provides conduit for advocacy & debate
3de Bach NW
Samenvatting p. 2/23
Offshore
Opito Cogent
• • • Non-profit industry-owned organisation Deliver innovative skills solutions in developing safe workforce of appropriate size & ability to meet business demands Areas of business o Emergency response standards & approval of training delivery o Endorsements of innovative products o Petroleum open learning: emergency response training for oil & gas industry o Workforce competence & technical standards & qualifications o Management of upstream modern apprenticeship scheme o Oil industry workforce skills development
Offshore structures
Fixed steel structure
• • • • • • • • Traditionally welded steel, tubular framework / jacket to support topside facilities Topside facilities vary slightly but include process equipment, power generation, helideck, accommodation & hotel services Single jacket installation in deep water environments Heli-deck & accommodation situated as far as possible from dangerous processing area Installation can consist of number of bridge-linked jackets (shallow water) In future restricted to development large fields in intermediate water depths Concrete structure = viable alternative but same disadvantages in deep water reserves High construction costs
Concrete gravity base structure
• • • • Construction commences in dry dock Design base includes void spaces / caissons to provide structure natural buoyancy (to tow to place) On location => void spaces flooded to facilitate positioning of base on seabed Void spaces may be pumped dry & used as storage compartments / filled with permanent ballast
Tension leg platform
• • • • Alternative to fixed steel structures & floating production systems for development of deep water oil & gas fields Role between fixed installation & floating production system Combines initial cost saving benefits with operational benefits Consists of floating production facility & tensioned legs
3de Bach NW
Samenvatting p. 3/23
Offshore
Semi-submersible vessel
• • • • • • Enormous box section barge supported on twin hulls Colossal capacity to consume water ballast Minimal water plane area => immovable object to wave action No effective main propulsion plant Some accurate manoeuvring capability Ideal for performing operations where accurate station keeping & exceptional stability needed
Floating production systems
• • • Floating oil rig All equipment used in conjunction with sub-sea wellheads One of three reasons o Small field o Isolated field o Field in very deep water Major advantage: lift anchors & depart
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Vessel types • • Both monohull & semi-submersible vessels Monohull o Coping strong winds & tides o Ample onboard storage capacity o Well suited to offloading duties Semi-submersibles o More stable o Greater production capacity o Can accommodate more people
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Vessel configurations • FSO – floating, storage and offloading unit o Storage tanker o Processed oil pumped from fixed platform with no storage capacity o Oil subsequently offloaded into shuttle tanker FPSO – floating, production, storage and offloading vessel o Replaces conventional platform entirely o Oil processed & stored on board o Advantages particularly in remote offshore locations with deep water, strong ocean currents & harsh weather conditions / installation pipelines not done o Can be floated off & re-used EPS – early production system o Progressed FPSO concept o Reduce time between discovery & production
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3de Bach NW • •
Samenvatting p. 4/23
Offshore
FPDSO – floating, production, drilling, storage and offloading vessel o Only advantages for compact field developments o Wells to far apart for drilling from single location PSV – production storage vessel o Designed for exploitation small fields located in moderate water depths o FPS & shuttle tanker in one o Dynamic positioning! o Storage tanks full => disengages from wellhead & sails to shore terminal
Shuttle tanker • • • Large proportion of service life loading, discharging & manoeuvring Manoeuvrability extremely important Next generation likely to facilitate drilling + ability for fast conversion to FSO / FPSO
VOC recovery • • • • VOC = volatile organic compound Emitted when loading Have to be removed Condensed in process plant & stored in separate tanks
Self-elevating jack-up
• • • • • • • • Triangular shaped box section barge with moveable legs Water depths up to 120 metres Shape imposes restrictions similar to semi-submersible vessels Thrusters units enables to maintain position Base each leg fitted with spud to spread load & prevent penetration in seabed Legs raised & lowered by means of rack & pinion arrangement Operation motors synchronised Primarily used for drilling operations o Majority used for exploration o Drilling of wells for permanent installations
3de Bach NW
Samenvatting p. 5/23
Offshore
Single point mooring
• • • • • Solution to problem of transferring crude oil from onshore reception facility / too large crude oil tankers Tankers moored to large buoy at considerable distance from coast Oil transferred from sub-sea pipeline through swivel connector into floating hoses Tanker = free to weathervain around buoy Still used extensively & more sophisticated designs developed (STL) o Submerged turret loading o Buoy moored to seabed o Pulled into & secured in mating cone in bottom of vessel o In buoy turret with connection to mooring & riser systems o Oil transferred through inline swivel via loading manifold to piping system of vessel o Disconnected => buoy will float in equilibrium position
Offshore vessels
Supply vessel
• • • • • • High bow & forward accommodation to withstand severest weather conditions & permit 360° unrestricted vision from wheelhouse Long flat afterdeck => ideal platform for stowage of containers, drill pipe & anchors Below deck: refrigerated cargo hold facilitates transportation of perishable foodstuffs & potable water Diesel fuel, cement & barites carried in purpose built tanks Personifies power & manoeuvrability Wheelhouse duplicate controls facing forward & aft
Stand-by vessel
• • • • All manned installations in UK sector need to have a stand-by vessel Capable of accommodating entire compliment of installation & provide first aid facilities At least 11 metres in length, speed of 10 knots, 360° unrestricted vision from wheelhouse, twin screw / single screw assisted with 360° thuster & bow thrusters Two fast rescue crafts available for immediate deployment
Anchor handling tug
• • • Towing operations at sea Stand-by operations Anchor handling
3de Bach NW
Samenvatting p. 6/23
Offshore
Anchor handling tug and supply vessel
• • • Bigger than usual anchor handling tug Can be used for supplying offshore production units Most of them with DP-system
Seismic vessel
• • Towing multiple streamers that contain hydrophones Air guns emit signals that travel through water, passes through strata (layers of sedimentary rock that form beds) with different seismic responses & filtering effects & returns to hydrophones
Remotely operated vehicle
• • • • • • • Underwater robots Unoccupied Highly manoeuvrable Operated by person aboard Linked to ship by tether Mostly equipped with o Video camera o Lights Additional equipment o Sonars o Magnetometers o Still camera o Manipulator / cutting arm o Water samplers o Instruments to measure water clarity, light penetration & temperature
Dive support vessel
• • • Large DP-capable vessel Multi-role function Variety of forms o Monohull o Flat-top barge configuration o Semi-submersible
3de Bach NW
Samenvatting p. 7/23
Offshore
Seabed tractors and trenchers
• • • • • Also ROVs Lay cable & complete bury operation Independently deployed to provide view of progress Carry out pipeline bury operations Carries o Cameras o Lights o Sonar facilities Can be rotated on suspension hooks
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Pipelay vessel
• • • • • On board construction by sequential welding of sections Vessel moves forward => pipeline descends in S-curve, partly covered by stinger / support gantry J-lay for deep water operations Reel-lay / drum-lay when pipe pre-constructed Flat-top / semi-submersible barges with anchors, now with DP
Crane barge
• Used for different purposes (e.g. pipelaying / installing / de-commissioning of platforms)
Rockdumper
• • • Variety of purposes o Precise bury operations (large bulkcarrier style vessels) o Erosion rectification projects (smaller deck-loading vessels) DP-system Commonest need = to provide protection to previously laid pipelines
Dredgers
• Functions o Channel & harbour maintenance o Recovery of roadstone & building aggregates o Creating land DP-capability Most are trailing suction type
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3de Bach NW
Samenvatting p. 8/23
Offshore
Cable lay and repair vessel
• • Number increased rapidly Task done by multi-purpose offshore support vessels, specially configured & mobilised for the purpose
Specialist crane vessels and work barges
• • • Crane vessel = specialised in lifting heavy loads Larger vessels often semi-submersible, also conventional monohulls are used Cranes can rotate
Drillships and rigs
• • Exploration drilling earliest application of Dynamic Positioning Locates onto worksite & commences drilling quicker with DP than with anchors
Function of a production platform
• • • Industrial town at sea Continuous hydrocarbon production Most important functions o Preparing for water / gas injection o Processing oil & gas o Cleaning produced water for disposal in sea o Generating power o Monitoring production systems for leaks Top each production well has Christmas tree Gas must be separated from oil Most platforms rest on steel supports Sub-sea collecting systems will be used more & more
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Refining crude oil
Introduction
• • • • Oil & gas hydrocarbons formed from remains of plants & other organisms between layers of sediment Seeped gradually through porous rock until reached impervious layer Oil in different parts => different proportion of various hydrocarbons Units o England: barrel = 36 imperial gallons o US: barrel = 31,5 gallons, petroleum barrel = 42 gallons
3de Bach NW
Samenvatting p. 9/23
Offshore
Refining
• • Refineries all over the world Crude oil separated into many substances by heat process
Fractional distillation
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Various components have different sizes, weights & boiling temperatures
3de Bach NW •
Samenvatting p. 10/23
Offshore
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Different steps o Mixture of substances with different boiling points heated to high temperature o When mixture boils => vapour formed, most substances into vapour phase o Vapour enters bottom of long column filled with trays / plates Trays have many holes or bubble caps to allow vapour to pass Trays increase contact time between vapour & liquids in column Trays help collect liquids Temperature difference across column o Vapour rises in column & cools o Substance reaches height where temperature column equals boiling point => liquefy o Trays collect various liquid fractions Pass to condensers Other areas for further chemical processing Useful for separating mixture of substances with narrow differences in boiling points
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Dynamic positioning
• • • • • • Dynamic positioning = system which automatically controls a vessel to maintain position & heading by means of active thrust Relatively new technology Vessel’s manoeuvrability was lower priority New needs in offshore oil & gas industry Not only maintaining position & heading, also follow precisely defined track, maintain position relative to moving target DP systems more sophisticated, complicated & reliable
3de Bach NW
Samenvatting p. 11/23
Offshore
The system
• • • Not just hardware / software => function / capability Includes all vessel components which contribute to function of station & heading keeping Vital element = provision of personnel competence
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Principles
• • • • • • Prime function = maintain position & heading Vessel has six freedoms of movement DP concerned with automatic control of surge, sway & yaw Difference between setpoint & feedback = error / offset Also used for automatic change of position & / / heading Some functions don’t relate to maintenance of fixed position & heading
Control console
• • • • Man-Machine Interface Location of all control input, buttons, switches, indicators, alarms screens … Located in variety of spaces Orientation not so important, but relative displays orientated in same way
3de Bach NW
Samenvatting p. 12/23
Offshore
Position reference systems
• • Central to DP function = establishment & maintenance of reliable, continuous & accurate position reference Most day-to-day navigation systems not accurate enough
Artemis Microwave PRS • • • Offshore loading operations Used for short range hydrographic & seismic survey Principles of operation o Obtaining range & bearing of mobile station from known fixed location o Low power microwave link established using directional tracking antennae o Continuous wave occulted to provide signal data o Time delays directly proportional to distance between fixed & mobile station o Fixed station on board platform, mobile located on vessel o Mobile station acts as master o Range measured @ mobile, bearing @ fixed transmitted to mobile
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o o Corrections applied for differences in location between antenna & centre of rotation of vessel Beacon operation o Many locations impossible to use standard Unit & antenna o Beacon = fixed slotted waveguide antenna within radome housing o Unit installed pointing in fixed direction o Horizontal beamwidth approximately 130° o Unit is just distace responder o Usually unmanned => beacon operation obtained from mobile unit once configured o Lower accuracy & resolution
3de Bach NW •
Samenvatting p. 13/23
Offshore
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Advantages and disadvantages o Advantages Long range High accuracy Possible to geographically reference position data Very convenient when inside 500 m zone o Disadvantages Requires fixed station established on nearby installation Fixed unit needs to be correctly calibrated & configured Specially designed units needed for hazardous areas Assistance from platform personnel to set up Interference from platform personnel Interference from heat / precipitation Line-of-sight interruption Vulnerable to power supply problem @ fixed end Interference from 3cm radar Statistics o Frequency: 9,2 – 9,3 GHz o Range: 10 m – 3000 m o Range accuracy: 0,1 m – 1,0 m depending upon range & environmental conditions o Bearing accuracy: 0,02 °
3de Bach NW
Samenvatting p. 14/23
Offshore
Laser-based position monitoring equipment • • Two systems on the market => Fanbeam & CyScan Fanbeam optical laser radar system o Principles of operation Use of specialised laser optics Two units: laser scanner & universal display unit Laser consists of array of gallium arsenide semiconductor laser diodes Laser with 20° vertical fan with horizontal divergence of less than 3 milliradians, pulsed at 7500 Hz Pulses collimated & emitted through transmitter lens Pulse length = 15 ns Reflected light directed onto array of photo sensitive diodes to produce electrical signal Range determined from echo ranging Laser contained within scanner unit, scans laser fan in horizontal Angle of laser unit measured by optical shaft encoder Resolution of 0,01° Whole assembly accuracy of 0,02° Scanning speed programmable Laser turned off at end of each scan to prevent direct viewing by anybody for more than brief period Allows small discrepancies in heights of scan unit & target Tilting of scan unit overcomes this offsets Scanner unit placed in location with unobstructed view Preferable above eye level & clear of salt sprays Interfaced to Universal Control Unit All controls necessary located on UCU Target may be any reflective surface o Advantages and disadvantages Advantages • Low cost • Ease of installation • Passive target • Target doesn’t require support services • High accuracy Disadvantages • Not operate with sun shining in lenses • Lenses affected by condensation, rain & salt spray • Impaired by fog, snow / heavy rain • Confused by bright lights close to target @ night • Interference from reflective items near target • Earlier models not easily reading in full daylight
3de Bach NW •
Samenvatting p. 15/23
Offshore
CyScan laser positioning system o Sophisticated range & bearing sensor system o Advantages in target acquisition & tracking o Contains advanced laser optics to produce wide vertically divergent beam with fine horizontal profile o Pulsed laser diode source operating at 940 nm o Maximum useful range of 400 m o Range resolution to 25 cm o Angular resolution = 0,006° o Sensor away from dust, smoke, water spray / radiant heat o Entirely software driven o No routine maintenance required other than ensuring optical window of sensor head is clean o Optimum range performance requires that targets are clean & in good conditions
Satellite-based position monitoring equipment • • DGPS widely adopted as position reference for DP vessels Global positioning system o Satellite-based passive ranging navigation system o Operates at 2 frequencies o System comprises 3 segments: control, space & user o Space segment: 24 satellites, 6 orbital planes, 12 hour orbit, altitude 20 200km o Timing of satellite transmissions is critical & controlled by caesium / rubidium frequency standards carried aboard o Control segment: ground monitor stations (track satellites in view & relay satellite range & phase data to master control station) o User segment: shipboard positioning receivers & monitoring systems o Pseudo-range: radio travel time between satellite & receiver converted into distance in meters o Determining clock offset => 4 satellites needed o Compute antenna position => resolve 4 unknowns: x, y, z & clock error o Referenced to WGS84 o Basic accuracy 5 – 20 meters, using P-code
3de Bach NW •
Samenvatting p. 16/23
Offshore
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Differential global positioning system o Enhance accuracy from GPS o Establishing reference stations at points with accurately known positions o Pseudo-ranges compared with computed => pseudo-range correction derived o Corrections included in message sent to ships receiver o Result in accuracy better than those obtained from P-code o Available from number of sources o Advantages & disadvantages to every type of link available VHF • Fastest correction update rates => highest accuracy • Range limited to 70 km MF • More versatile due to larger availability of IALA beacons • Ranges up to 300 – 600 km • Extra coverage at expense of update rate • More susceptible to interference by weather & dawn/dusk Communication satellites • Most flexible DGPS link solution • Maximum range only limited by theoretical application of corrections • Ability to move between projects without changing equipment & contractor • Little degradation of accuracy o Accuracy between 1 – 5 m o Most reliable when vessel is in open water o Receiving antenna in highest point @ vessel o Interference caused by telex, mobile phones, satcom kit / radar Relative GPS o Positioning relative to moving position o Seatex DARPS FPSO uses DGPS to monitor absolute position Shuttle tanker determines absolute & relative position Differential corrections not used => same for both Dual UHF transponder placed on point of reference & shuttle tanker receives GPS data Comparison between GPS position of transponder & GPS position of tanker => range / bearing vector o DARPS 102 Improve accuracy of basic system by use of dual-frequency GPS Real-time compensation of errors by high ionospheric activity Corrections are input from dual-frequency reference stations Accuracies: 1,0 m in position, 0,05 m / sec in velocity o Link has range of 2 – 3 km
3de Bach NW •
Samenvatting p. 17/23
Offshore
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Glonass o Russian counterpart o Space segment: 24 satellites, 3 orbit planes, inclination 64,8°, 25 510 km, orbital period 11h 15min o Principals & practice cfr GPS o Each satellite at own frequency o PZ90 & UTC-SU o No official transformations but empirically determined o Better availability in higher latitudes o Satellite availability fallen drastically Difference Glonass system o Similar to DGPS o Rate of change of errors = lower => lower update rates necessary Combined GPS / Glonass operation o More than 15 satellites in view simultaneously o Gives greater reliability
Taut wire position reference system • • • • • Useful short range position reference Useful when vessel spends long periods in static location & limited water depth Also useful when vessel needs to maintain position relative to moving vehicle Number of configurations Commonest configuration o Crane assembly on deck, usually at side of vessel o Depressor weight on wire rope handled by constant-tension winch o Wire passes from spooling drum, lead over sheaves onto boom / A-frame projecting over side of vessel o End of boom: angle sensors to detect angle of wire when in operation Practice of using taut wires for position reference o Short range o Limitations in both deep & shallow water o Requires certain amount of planning o Limitations on wire angle because of risk of dragging o Wire scope limitations due physical design of vessel & location of taut wire o Planning deployment of taut wire carefully in relation to seabed structure & hardware o Degradation in accuracy in relation to strength of tide o System dependent on wire being straight => wire must be rigid
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3de Bach NW
Samenvatting p. 18/23
Offshore
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3de Bach NW •
Samenvatting p. 19/23
Offshore
Advantages & disadvantages o Advantages High accuracy, especially in moderate water depths Good reliability Quick & easy to set up No need for assistance from external sources to set up / operate System is mechanical, on-board repair = possible o Disadvantages Short range only Susceptible to strong tides Accuracy deteriorates in deep water Maximum depth limitation Adversely affected by surface debris / ice conditions Possibility of weight dragging => positional errors Fouled by ROV, divers / other underwater activity Provide obstruction to underwater operations Possibility of depressor weight landing on seabed hardware Not geographically referenced Vessel needs to move => constant resetting of taut wire Susceptible to mechanical damage Limitations in range due to vessel’s structure Wire cannot be eyeballed Reliant upon vessel main power
Hydroacoustic position reference systems • • • • Well established medium for many applications Range measurement related to time travel Not only used for DP, also for tracking of underwater vehicles / equipment, marking for re-location of underwater features / hardware, control of subsea equipment Ultrashort / Supershort baseline hydroacoustic position reference o Transmit & reveive elements combined in one hull-mounted transducer o Communicates at acoustic frequencies with subsea transponders o Basic configuration: control & display unit, transducer unit, transponder o Position measurement based upon range & directional data o Range measuring by time elapsed between transmission & reception o Direction measured at transducer as source direction of reply signal o Determined from time-phase comparisons between pairs of transducer receiving elements within transducer head o Transducers Located at end of probe projecting 4 m beneath keel Carried by hull unit mounted atop gate valve Includes inspection chamber allowing access to retracted transducer head Electric actuation motor with sprocket chain drive Partial extension of probe possible => acoustic element close to hull plating & sources of acoustic noise & reflecting surface
3de Bach NW
Samenvatting p. 20/23
Offshore
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While searching for target: wide beam, transponder received: narrow beam Conditions poor when rolling in bad weather o Transponders Battery powered Battery life is limited, depends upon type of battery, functions available, low / high power operation & interrogation rate Total of 56 channels Different extra functions can be fitted (e.g. temperature sensor, inclinometer) Miniature & sub-miniature transponders for use on ROV’s Responder • Same function as transponder • Interrogated by hard wire from surface • Useful when operating ROV’s • Interrogation signal more secure carried, reply = through water o Transponder deployment Placed in fixed locations on seabed, marking wellheads / other targets Array of transponders around offshore loading terminal Temporary use: vessel lays transponders Care taken when deploying Not lowering on seabed hardware / locations with acoustic shadowing Keep in mind acoustic path between transducer & transponder o Applications Tracking of ROV’s & other targets In conjunction with DP Follow subsea target Drilling rigs => inclinometer to ensure correct drilling Offshore loading terminals for positioning of shuttle tankers Variety of underwater positioning functions Long baseline hydroacoustic position reference o Array of transponders placed upon seabed o Once calibrated, individual interrogation => series of ranges to transponders o No angle measurements required o Range measurement errors less significant o Higher accuracy o Co-ordinate system = attached to seabed o Minimum number needed = 3, normally 6 or more o Depth of transducer is known variable o System can operate independently of VRU input o Common interrogation frequency, individual reply frequencies determined by transponders’ channel numbers o Decoding delay set individually Short baseline hydroacoustic position reference o Typically installed in drilling rigs & semi-submersible barges o Number of different principles used o All based upon hydrophones / transducers in array upon vessel bottom
3de Bach NW
Samenvatting p. 21/23
Offshore
o Distance between individual elements made as large as practicable o Beacon not interrogated but emits at regular intervals o Greater accuracy in deep water than USBL
3de Bach NW •
Samenvatting p. 22/23
Offshore
Multi-user long baseline hydroacoustic position reference o Acoustic saturation = problem (deep-water oilfield areas) o Heavy usage of acoustic techniques => interference o Multi-user system = solution o Array of 5 transponders o Master beacon located at centre & emits acoustic interrogation signals at regular intervals on specific interrogation frequency o Signals received by other transponders & surface vessel o No interrogation from surface o Slave transponders receive signals => reply signals after coding delay at specific acoustic frequencies o Observed time differences => position of vessel relative to array o Update rate may be increased o Simultaneous use is possible
Radio position reference systems • • • Accuracy lower than systems above Coverage limited to immediate environs of field Syledis o Medium range system operating in UHF band o Network of shore stations / beacons & mobile receiving stations o Array format include 5 – 60 stations o Multi-user capability o Range up to 80 miles o Accuracy of 1 – 3 m Microfix o Short range position fixing survey system using microwave techniques o Accuracy of 1 m o Range up to 50 miles o Line-of-sight operation necessary o Multi-user capability Argo o HF positioning system using single frequency o Frequency time-shared within array of shore & mobile stations in coverage o One shore station designated as master station & transmits synchronisation pulse o All shore stations transmit time-share phase locked signals o Phase differences => range measurements o Update rate 2 s o Multi-user capability o Accuracy 5 m o Range 200 miles by night, 450 miles by day o Affected by sky wave interference
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3de Bach NW •
Samenvatting p. 23/23
Offshore
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Pulse-8 o Permanently operating chains o Similar operating characteristics to Loran-C system o Principle of time-difference measurements between pulsed signals received from shore stations o Accuracy of 50 m o Range up to 500 miles o Multi-user capability Log reference o Integration Doppler speed log into DP as reference o Log is no position reference o May provide useful velocity indicator o Reduce vessel’s velocity to zero in both axes o Log input must be heavily filtered o Unreliable when manoeuvring at low speeds o Water movement & aeration can affect log outputs greatly
REMARK: I didn’t include all chapters! The chapters not included should be read.
Samenvatting p. 1/23
Offshore
Organisations
UKOOA – United Kingdom Offshore Operators Association
• • • Representative organisation for UK offshore oil & gas industry Members = companies licensed by Government to explore for & produce oil & gas Forum to deal with common interests & problems
IOOA – Irish Offshore Operator’s Association
• • • • Umbrella organisation Represents oil & gas companies with operating interests in Ireland’s offshore industry Forum to work together in identifying & tackling issues (such as safety, environment, legislation & employment) Focal point for liaison between companies & industry itself
NAPE – Nigerian Association of Petroleum Explorationists
• • • • Non-profit organisation Objectives & membership governed by Bye-Laws Activities supported by corporate membership grants & donations Cause of educational development of students & professionals
NOGEPA – Netherlands Oil & Gas Exploration & Production Association
• • • • Promote common interests of all companies holding licences to explore for, develop & produce hydrocarbons on- & offshore in the Netherlands Provides means of communication with Government, media & other third parties Coordinates industry efforts to assume safety & health of people & protection of environment Main activities carried out in committees & workgroups
OGP – International Association of Oil & Gas Producers
• • • • • Encompasses world’s leading publicly traded, private & state-owned oil & gas associations More than half world’s oil & one third gas Develop effective communications between industry & international regulations Represents interests of industry before international regulators & legislators Provides conduit for advocacy & debate
3de Bach NW
Samenvatting p. 2/23
Offshore
Opito Cogent
• • • Non-profit industry-owned organisation Deliver innovative skills solutions in developing safe workforce of appropriate size & ability to meet business demands Areas of business o Emergency response standards & approval of training delivery o Endorsements of innovative products o Petroleum open learning: emergency response training for oil & gas industry o Workforce competence & technical standards & qualifications o Management of upstream modern apprenticeship scheme o Oil industry workforce skills development
Offshore structures
Fixed steel structure
• • • • • • • • Traditionally welded steel, tubular framework / jacket to support topside facilities Topside facilities vary slightly but include process equipment, power generation, helideck, accommodation & hotel services Single jacket installation in deep water environments Heli-deck & accommodation situated as far as possible from dangerous processing area Installation can consist of number of bridge-linked jackets (shallow water) In future restricted to development large fields in intermediate water depths Concrete structure = viable alternative but same disadvantages in deep water reserves High construction costs
Concrete gravity base structure
• • • • Construction commences in dry dock Design base includes void spaces / caissons to provide structure natural buoyancy (to tow to place) On location => void spaces flooded to facilitate positioning of base on seabed Void spaces may be pumped dry & used as storage compartments / filled with permanent ballast
Tension leg platform
• • • • Alternative to fixed steel structures & floating production systems for development of deep water oil & gas fields Role between fixed installation & floating production system Combines initial cost saving benefits with operational benefits Consists of floating production facility & tensioned legs
3de Bach NW
Samenvatting p. 3/23
Offshore
Semi-submersible vessel
• • • • • • Enormous box section barge supported on twin hulls Colossal capacity to consume water ballast Minimal water plane area => immovable object to wave action No effective main propulsion plant Some accurate manoeuvring capability Ideal for performing operations where accurate station keeping & exceptional stability needed
Floating production systems
• • • Floating oil rig All equipment used in conjunction with sub-sea wellheads One of three reasons o Small field o Isolated field o Field in very deep water Major advantage: lift anchors & depart
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Vessel types • • Both monohull & semi-submersible vessels Monohull o Coping strong winds & tides o Ample onboard storage capacity o Well suited to offloading duties Semi-submersibles o More stable o Greater production capacity o Can accommodate more people
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Vessel configurations • FSO – floating, storage and offloading unit o Storage tanker o Processed oil pumped from fixed platform with no storage capacity o Oil subsequently offloaded into shuttle tanker FPSO – floating, production, storage and offloading vessel o Replaces conventional platform entirely o Oil processed & stored on board o Advantages particularly in remote offshore locations with deep water, strong ocean currents & harsh weather conditions / installation pipelines not done o Can be floated off & re-used EPS – early production system o Progressed FPSO concept o Reduce time between discovery & production
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3de Bach NW • •
Samenvatting p. 4/23
Offshore
FPDSO – floating, production, drilling, storage and offloading vessel o Only advantages for compact field developments o Wells to far apart for drilling from single location PSV – production storage vessel o Designed for exploitation small fields located in moderate water depths o FPS & shuttle tanker in one o Dynamic positioning! o Storage tanks full => disengages from wellhead & sails to shore terminal
Shuttle tanker • • • Large proportion of service life loading, discharging & manoeuvring Manoeuvrability extremely important Next generation likely to facilitate drilling + ability for fast conversion to FSO / FPSO
VOC recovery • • • • VOC = volatile organic compound Emitted when loading Have to be removed Condensed in process plant & stored in separate tanks
Self-elevating jack-up
• • • • • • • • Triangular shaped box section barge with moveable legs Water depths up to 120 metres Shape imposes restrictions similar to semi-submersible vessels Thrusters units enables to maintain position Base each leg fitted with spud to spread load & prevent penetration in seabed Legs raised & lowered by means of rack & pinion arrangement Operation motors synchronised Primarily used for drilling operations o Majority used for exploration o Drilling of wells for permanent installations
3de Bach NW
Samenvatting p. 5/23
Offshore
Single point mooring
• • • • • Solution to problem of transferring crude oil from onshore reception facility / too large crude oil tankers Tankers moored to large buoy at considerable distance from coast Oil transferred from sub-sea pipeline through swivel connector into floating hoses Tanker = free to weathervain around buoy Still used extensively & more sophisticated designs developed (STL) o Submerged turret loading o Buoy moored to seabed o Pulled into & secured in mating cone in bottom of vessel o In buoy turret with connection to mooring & riser systems o Oil transferred through inline swivel via loading manifold to piping system of vessel o Disconnected => buoy will float in equilibrium position
Offshore vessels
Supply vessel
• • • • • • High bow & forward accommodation to withstand severest weather conditions & permit 360° unrestricted vision from wheelhouse Long flat afterdeck => ideal platform for stowage of containers, drill pipe & anchors Below deck: refrigerated cargo hold facilitates transportation of perishable foodstuffs & potable water Diesel fuel, cement & barites carried in purpose built tanks Personifies power & manoeuvrability Wheelhouse duplicate controls facing forward & aft
Stand-by vessel
• • • • All manned installations in UK sector need to have a stand-by vessel Capable of accommodating entire compliment of installation & provide first aid facilities At least 11 metres in length, speed of 10 knots, 360° unrestricted vision from wheelhouse, twin screw / single screw assisted with 360° thuster & bow thrusters Two fast rescue crafts available for immediate deployment
Anchor handling tug
• • • Towing operations at sea Stand-by operations Anchor handling
3de Bach NW
Samenvatting p. 6/23
Offshore
Anchor handling tug and supply vessel
• • • Bigger than usual anchor handling tug Can be used for supplying offshore production units Most of them with DP-system
Seismic vessel
• • Towing multiple streamers that contain hydrophones Air guns emit signals that travel through water, passes through strata (layers of sedimentary rock that form beds) with different seismic responses & filtering effects & returns to hydrophones
Remotely operated vehicle
• • • • • • • Underwater robots Unoccupied Highly manoeuvrable Operated by person aboard Linked to ship by tether Mostly equipped with o Video camera o Lights Additional equipment o Sonars o Magnetometers o Still camera o Manipulator / cutting arm o Water samplers o Instruments to measure water clarity, light penetration & temperature
Dive support vessel
• • • Large DP-capable vessel Multi-role function Variety of forms o Monohull o Flat-top barge configuration o Semi-submersible
3de Bach NW
Samenvatting p. 7/23
Offshore
Seabed tractors and trenchers
• • • • • Also ROVs Lay cable & complete bury operation Independently deployed to provide view of progress Carry out pipeline bury operations Carries o Cameras o Lights o Sonar facilities Can be rotated on suspension hooks
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Pipelay vessel
• • • • • On board construction by sequential welding of sections Vessel moves forward => pipeline descends in S-curve, partly covered by stinger / support gantry J-lay for deep water operations Reel-lay / drum-lay when pipe pre-constructed Flat-top / semi-submersible barges with anchors, now with DP
Crane barge
• Used for different purposes (e.g. pipelaying / installing / de-commissioning of platforms)
Rockdumper
• • • Variety of purposes o Precise bury operations (large bulkcarrier style vessels) o Erosion rectification projects (smaller deck-loading vessels) DP-system Commonest need = to provide protection to previously laid pipelines
Dredgers
• Functions o Channel & harbour maintenance o Recovery of roadstone & building aggregates o Creating land DP-capability Most are trailing suction type
• •
3de Bach NW
Samenvatting p. 8/23
Offshore
Cable lay and repair vessel
• • Number increased rapidly Task done by multi-purpose offshore support vessels, specially configured & mobilised for the purpose
Specialist crane vessels and work barges
• • • Crane vessel = specialised in lifting heavy loads Larger vessels often semi-submersible, also conventional monohulls are used Cranes can rotate
Drillships and rigs
• • Exploration drilling earliest application of Dynamic Positioning Locates onto worksite & commences drilling quicker with DP than with anchors
Function of a production platform
• • • Industrial town at sea Continuous hydrocarbon production Most important functions o Preparing for water / gas injection o Processing oil & gas o Cleaning produced water for disposal in sea o Generating power o Monitoring production systems for leaks Top each production well has Christmas tree Gas must be separated from oil Most platforms rest on steel supports Sub-sea collecting systems will be used more & more
• • • •
Refining crude oil
Introduction
• • • • Oil & gas hydrocarbons formed from remains of plants & other organisms between layers of sediment Seeped gradually through porous rock until reached impervious layer Oil in different parts => different proportion of various hydrocarbons Units o England: barrel = 36 imperial gallons o US: barrel = 31,5 gallons, petroleum barrel = 42 gallons
3de Bach NW
Samenvatting p. 9/23
Offshore
Refining
• • Refineries all over the world Crude oil separated into many substances by heat process
Fractional distillation
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• •
Various components have different sizes, weights & boiling temperatures
3de Bach NW •
Samenvatting p. 10/23
Offshore
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Different steps o Mixture of substances with different boiling points heated to high temperature o When mixture boils => vapour formed, most substances into vapour phase o Vapour enters bottom of long column filled with trays / plates Trays have many holes or bubble caps to allow vapour to pass Trays increase contact time between vapour & liquids in column Trays help collect liquids Temperature difference across column o Vapour rises in column & cools o Substance reaches height where temperature column equals boiling point => liquefy o Trays collect various liquid fractions Pass to condensers Other areas for further chemical processing Useful for separating mixture of substances with narrow differences in boiling points
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Dynamic positioning
• • • • • • Dynamic positioning = system which automatically controls a vessel to maintain position & heading by means of active thrust Relatively new technology Vessel’s manoeuvrability was lower priority New needs in offshore oil & gas industry Not only maintaining position & heading, also follow precisely defined track, maintain position relative to moving target DP systems more sophisticated, complicated & reliable
3de Bach NW
Samenvatting p. 11/23
Offshore
The system
• • • Not just hardware / software => function / capability Includes all vessel components which contribute to function of station & heading keeping Vital element = provision of personnel competence
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Principles
• • • • • • Prime function = maintain position & heading Vessel has six freedoms of movement DP concerned with automatic control of surge, sway & yaw Difference between setpoint & feedback = error / offset Also used for automatic change of position & / / heading Some functions don’t relate to maintenance of fixed position & heading
Control console
• • • • Man-Machine Interface Location of all control input, buttons, switches, indicators, alarms screens … Located in variety of spaces Orientation not so important, but relative displays orientated in same way
3de Bach NW
Samenvatting p. 12/23
Offshore
Position reference systems
• • Central to DP function = establishment & maintenance of reliable, continuous & accurate position reference Most day-to-day navigation systems not accurate enough
Artemis Microwave PRS • • • Offshore loading operations Used for short range hydrographic & seismic survey Principles of operation o Obtaining range & bearing of mobile station from known fixed location o Low power microwave link established using directional tracking antennae o Continuous wave occulted to provide signal data o Time delays directly proportional to distance between fixed & mobile station o Fixed station on board platform, mobile located on vessel o Mobile station acts as master o Range measured @ mobile, bearing @ fixed transmitted to mobile
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o o Corrections applied for differences in location between antenna & centre of rotation of vessel Beacon operation o Many locations impossible to use standard Unit & antenna o Beacon = fixed slotted waveguide antenna within radome housing o Unit installed pointing in fixed direction o Horizontal beamwidth approximately 130° o Unit is just distace responder o Usually unmanned => beacon operation obtained from mobile unit once configured o Lower accuracy & resolution
3de Bach NW •
Samenvatting p. 13/23
Offshore
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Advantages and disadvantages o Advantages Long range High accuracy Possible to geographically reference position data Very convenient when inside 500 m zone o Disadvantages Requires fixed station established on nearby installation Fixed unit needs to be correctly calibrated & configured Specially designed units needed for hazardous areas Assistance from platform personnel to set up Interference from platform personnel Interference from heat / precipitation Line-of-sight interruption Vulnerable to power supply problem @ fixed end Interference from 3cm radar Statistics o Frequency: 9,2 – 9,3 GHz o Range: 10 m – 3000 m o Range accuracy: 0,1 m – 1,0 m depending upon range & environmental conditions o Bearing accuracy: 0,02 °
3de Bach NW
Samenvatting p. 14/23
Offshore
Laser-based position monitoring equipment • • Two systems on the market => Fanbeam & CyScan Fanbeam optical laser radar system o Principles of operation Use of specialised laser optics Two units: laser scanner & universal display unit Laser consists of array of gallium arsenide semiconductor laser diodes Laser with 20° vertical fan with horizontal divergence of less than 3 milliradians, pulsed at 7500 Hz Pulses collimated & emitted through transmitter lens Pulse length = 15 ns Reflected light directed onto array of photo sensitive diodes to produce electrical signal Range determined from echo ranging Laser contained within scanner unit, scans laser fan in horizontal Angle of laser unit measured by optical shaft encoder Resolution of 0,01° Whole assembly accuracy of 0,02° Scanning speed programmable Laser turned off at end of each scan to prevent direct viewing by anybody for more than brief period Allows small discrepancies in heights of scan unit & target Tilting of scan unit overcomes this offsets Scanner unit placed in location with unobstructed view Preferable above eye level & clear of salt sprays Interfaced to Universal Control Unit All controls necessary located on UCU Target may be any reflective surface o Advantages and disadvantages Advantages • Low cost • Ease of installation • Passive target • Target doesn’t require support services • High accuracy Disadvantages • Not operate with sun shining in lenses • Lenses affected by condensation, rain & salt spray • Impaired by fog, snow / heavy rain • Confused by bright lights close to target @ night • Interference from reflective items near target • Earlier models not easily reading in full daylight
3de Bach NW •
Samenvatting p. 15/23
Offshore
CyScan laser positioning system o Sophisticated range & bearing sensor system o Advantages in target acquisition & tracking o Contains advanced laser optics to produce wide vertically divergent beam with fine horizontal profile o Pulsed laser diode source operating at 940 nm o Maximum useful range of 400 m o Range resolution to 25 cm o Angular resolution = 0,006° o Sensor away from dust, smoke, water spray / radiant heat o Entirely software driven o No routine maintenance required other than ensuring optical window of sensor head is clean o Optimum range performance requires that targets are clean & in good conditions
Satellite-based position monitoring equipment • • DGPS widely adopted as position reference for DP vessels Global positioning system o Satellite-based passive ranging navigation system o Operates at 2 frequencies o System comprises 3 segments: control, space & user o Space segment: 24 satellites, 6 orbital planes, 12 hour orbit, altitude 20 200km o Timing of satellite transmissions is critical & controlled by caesium / rubidium frequency standards carried aboard o Control segment: ground monitor stations (track satellites in view & relay satellite range & phase data to master control station) o User segment: shipboard positioning receivers & monitoring systems o Pseudo-range: radio travel time between satellite & receiver converted into distance in meters o Determining clock offset => 4 satellites needed o Compute antenna position => resolve 4 unknowns: x, y, z & clock error o Referenced to WGS84 o Basic accuracy 5 – 20 meters, using P-code
3de Bach NW •
Samenvatting p. 16/23
Offshore
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Differential global positioning system o Enhance accuracy from GPS o Establishing reference stations at points with accurately known positions o Pseudo-ranges compared with computed => pseudo-range correction derived o Corrections included in message sent to ships receiver o Result in accuracy better than those obtained from P-code o Available from number of sources o Advantages & disadvantages to every type of link available VHF • Fastest correction update rates => highest accuracy • Range limited to 70 km MF • More versatile due to larger availability of IALA beacons • Ranges up to 300 – 600 km • Extra coverage at expense of update rate • More susceptible to interference by weather & dawn/dusk Communication satellites • Most flexible DGPS link solution • Maximum range only limited by theoretical application of corrections • Ability to move between projects without changing equipment & contractor • Little degradation of accuracy o Accuracy between 1 – 5 m o Most reliable when vessel is in open water o Receiving antenna in highest point @ vessel o Interference caused by telex, mobile phones, satcom kit / radar Relative GPS o Positioning relative to moving position o Seatex DARPS FPSO uses DGPS to monitor absolute position Shuttle tanker determines absolute & relative position Differential corrections not used => same for both Dual UHF transponder placed on point of reference & shuttle tanker receives GPS data Comparison between GPS position of transponder & GPS position of tanker => range / bearing vector o DARPS 102 Improve accuracy of basic system by use of dual-frequency GPS Real-time compensation of errors by high ionospheric activity Corrections are input from dual-frequency reference stations Accuracies: 1,0 m in position, 0,05 m / sec in velocity o Link has range of 2 – 3 km
3de Bach NW •
Samenvatting p. 17/23
Offshore
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Glonass o Russian counterpart o Space segment: 24 satellites, 3 orbit planes, inclination 64,8°, 25 510 km, orbital period 11h 15min o Principals & practice cfr GPS o Each satellite at own frequency o PZ90 & UTC-SU o No official transformations but empirically determined o Better availability in higher latitudes o Satellite availability fallen drastically Difference Glonass system o Similar to DGPS o Rate of change of errors = lower => lower update rates necessary Combined GPS / Glonass operation o More than 15 satellites in view simultaneously o Gives greater reliability
Taut wire position reference system • • • • • Useful short range position reference Useful when vessel spends long periods in static location & limited water depth Also useful when vessel needs to maintain position relative to moving vehicle Number of configurations Commonest configuration o Crane assembly on deck, usually at side of vessel o Depressor weight on wire rope handled by constant-tension winch o Wire passes from spooling drum, lead over sheaves onto boom / A-frame projecting over side of vessel o End of boom: angle sensors to detect angle of wire when in operation Practice of using taut wires for position reference o Short range o Limitations in both deep & shallow water o Requires certain amount of planning o Limitations on wire angle because of risk of dragging o Wire scope limitations due physical design of vessel & location of taut wire o Planning deployment of taut wire carefully in relation to seabed structure & hardware o Degradation in accuracy in relation to strength of tide o System dependent on wire being straight => wire must be rigid
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3de Bach NW
Samenvatting p. 18/23
Offshore
o
3de Bach NW •
Samenvatting p. 19/23
Offshore
Advantages & disadvantages o Advantages High accuracy, especially in moderate water depths Good reliability Quick & easy to set up No need for assistance from external sources to set up / operate System is mechanical, on-board repair = possible o Disadvantages Short range only Susceptible to strong tides Accuracy deteriorates in deep water Maximum depth limitation Adversely affected by surface debris / ice conditions Possibility of weight dragging => positional errors Fouled by ROV, divers / other underwater activity Provide obstruction to underwater operations Possibility of depressor weight landing on seabed hardware Not geographically referenced Vessel needs to move => constant resetting of taut wire Susceptible to mechanical damage Limitations in range due to vessel’s structure Wire cannot be eyeballed Reliant upon vessel main power
Hydroacoustic position reference systems • • • • Well established medium for many applications Range measurement related to time travel Not only used for DP, also for tracking of underwater vehicles / equipment, marking for re-location of underwater features / hardware, control of subsea equipment Ultrashort / Supershort baseline hydroacoustic position reference o Transmit & reveive elements combined in one hull-mounted transducer o Communicates at acoustic frequencies with subsea transponders o Basic configuration: control & display unit, transducer unit, transponder o Position measurement based upon range & directional data o Range measuring by time elapsed between transmission & reception o Direction measured at transducer as source direction of reply signal o Determined from time-phase comparisons between pairs of transducer receiving elements within transducer head o Transducers Located at end of probe projecting 4 m beneath keel Carried by hull unit mounted atop gate valve Includes inspection chamber allowing access to retracted transducer head Electric actuation motor with sprocket chain drive Partial extension of probe possible => acoustic element close to hull plating & sources of acoustic noise & reflecting surface
3de Bach NW
Samenvatting p. 20/23
Offshore
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While searching for target: wide beam, transponder received: narrow beam Conditions poor when rolling in bad weather o Transponders Battery powered Battery life is limited, depends upon type of battery, functions available, low / high power operation & interrogation rate Total of 56 channels Different extra functions can be fitted (e.g. temperature sensor, inclinometer) Miniature & sub-miniature transponders for use on ROV’s Responder • Same function as transponder • Interrogated by hard wire from surface • Useful when operating ROV’s • Interrogation signal more secure carried, reply = through water o Transponder deployment Placed in fixed locations on seabed, marking wellheads / other targets Array of transponders around offshore loading terminal Temporary use: vessel lays transponders Care taken when deploying Not lowering on seabed hardware / locations with acoustic shadowing Keep in mind acoustic path between transducer & transponder o Applications Tracking of ROV’s & other targets In conjunction with DP Follow subsea target Drilling rigs => inclinometer to ensure correct drilling Offshore loading terminals for positioning of shuttle tankers Variety of underwater positioning functions Long baseline hydroacoustic position reference o Array of transponders placed upon seabed o Once calibrated, individual interrogation => series of ranges to transponders o No angle measurements required o Range measurement errors less significant o Higher accuracy o Co-ordinate system = attached to seabed o Minimum number needed = 3, normally 6 or more o Depth of transducer is known variable o System can operate independently of VRU input o Common interrogation frequency, individual reply frequencies determined by transponders’ channel numbers o Decoding delay set individually Short baseline hydroacoustic position reference o Typically installed in drilling rigs & semi-submersible barges o Number of different principles used o All based upon hydrophones / transducers in array upon vessel bottom
3de Bach NW
Samenvatting p. 21/23
Offshore
o Distance between individual elements made as large as practicable o Beacon not interrogated but emits at regular intervals o Greater accuracy in deep water than USBL
3de Bach NW •
Samenvatting p. 22/23
Offshore
Multi-user long baseline hydroacoustic position reference o Acoustic saturation = problem (deep-water oilfield areas) o Heavy usage of acoustic techniques => interference o Multi-user system = solution o Array of 5 transponders o Master beacon located at centre & emits acoustic interrogation signals at regular intervals on specific interrogation frequency o Signals received by other transponders & surface vessel o No interrogation from surface o Slave transponders receive signals => reply signals after coding delay at specific acoustic frequencies o Observed time differences => position of vessel relative to array o Update rate may be increased o Simultaneous use is possible
Radio position reference systems • • • Accuracy lower than systems above Coverage limited to immediate environs of field Syledis o Medium range system operating in UHF band o Network of shore stations / beacons & mobile receiving stations o Array format include 5 – 60 stations o Multi-user capability o Range up to 80 miles o Accuracy of 1 – 3 m Microfix o Short range position fixing survey system using microwave techniques o Accuracy of 1 m o Range up to 50 miles o Line-of-sight operation necessary o Multi-user capability Argo o HF positioning system using single frequency o Frequency time-shared within array of shore & mobile stations in coverage o One shore station designated as master station & transmits synchronisation pulse o All shore stations transmit time-share phase locked signals o Phase differences => range measurements o Update rate 2 s o Multi-user capability o Accuracy 5 m o Range 200 miles by night, 450 miles by day o Affected by sky wave interference
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3de Bach NW •
Samenvatting p. 23/23
Offshore
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Pulse-8 o Permanently operating chains o Similar operating characteristics to Loran-C system o Principle of time-difference measurements between pulsed signals received from shore stations o Accuracy of 50 m o Range up to 500 miles o Multi-user capability Log reference o Integration Doppler speed log into DP as reference o Log is no position reference o May provide useful velocity indicator o Reduce vessel’s velocity to zero in both axes o Log input must be heavily filtered o Unreliable when manoeuvring at low speeds o Water movement & aeration can affect log outputs greatly
REMARK: I didn’t include all chapters! The chapters not included should be read.
