DEEP WATER RISER TECHNOLOGY, VIV FATIGUE MANAGEMENT

Document Sample
DEEP WATER RISER TECHNOLOGY, VIV FATIGUE MANAGEMENT Powered By Docstoc
					       DEEP WATER RISER                                              SCOPE OF PRESENTATION
       TECHNOLOGY, VIV
    & FATIGUE MANAGEMENT                                         n Deep Water Riser Design Issues
                                                                 n AMJIG Guidelines
                                                                 n Guideline Applications and Findings
              by Dr Frank Lim                                    n Analysis Limitations
       2H Offshore Engineering Limited                           n VIV Prediction and Effects
                                                                 n Fatigue Management and Riser Monitoring
               Slender Well Workshop
               Aberdeen, March 1999




            DEEP WATER
                                                                                 1 YEAR CURRENTS
           ENVIRONMENTS
                                                                                                          1500
                                                                             Elevation Above Seabed (m)



      35
                             West of Shetland
      30           Voring Basin                                                                                                        WoS
                                                                                                          1000
      25                                                                                                                               Brazil
                                          Gulf of Mexico
      20                                                                                                                               GoM Loop
                                                                                                           500
                                                                                                                                       West Africa
      15

      10
              West Africa            Campos Basin                                                            0
       5                                                                                                         0        1        2
        1.2      1.4        1.6     1.8         2   2.2    2.4
                                                                                                                 Current Speed (m/s)
                 100 yr Surface Current Speed (m/s)




                                                                     AMJIG - Deep Water Drilling
DEEP WATER CHALLENGES                                                 Riser Integrity Management
                                                                               Guidelines
n Riser curvature and wear increased
n Buoyancy effectiveness reduced                                 n Extension NOT replacement for existing
                                                                   guidance
n Mud pressures increased
                                                                 n Emphasis on system approach:
n Collapse pressures increased
                                                                     u   All components - riser, wellhead, conductor
n Base/disconnect tension at BOP increased
                                                                     u   All operations - riser installation, operations,
n Hang-off deflections increased                                         monitoring , inspection
n Running and retrieval takes longer
n Fatigue damage increased




                                                                                                                                                     1
    AMJIG RISER GUIDELINE
                                                    PART I - RISER ANALYSIS
        DEVELOPMENT
n Directed by BP, Shell and Elf                 n Riser configuration
n Reviewed by operators, drilling contractors   n Drilling and survival limits
  and analysis consultants                      n Completion and well test operations
n Guidelines in 3 Parts:                        n Riser VIV
    u Analysis                                  n Riser-wellhead-conductor interaction
    u Operations
                                                n Recoil and hang-off
    u Inspection
                                                n Riser, casing and conductor installation




            PART II - RISER
                                                        PART III - INSPECTION
             OPERATIONS
n Tension and tension variation                 n   Inspection Assessment
n Installation and retrieval envelopes              u Service category
n Drilling and survival envelopes                   u Usage history
                                                    u Inspection types and frequency
n Monitoring operating conditions
                                                    u Acceptance criteria
n Recording riser operations
                                                    u Provision for inspection
n Recording riser usage
                                                n Components to be Inspected
                                                n Inspection Procedures by OCTG




                                                         DEEP WATER RISER
 GUIDELINE APPLICATIONS
                                                             FINDINGS
n Assess fitness-for-purpose                    n Need thicker walls for internal and external
n Optimise riser configuration                    pressures and tension
n Predict downtime                              n Hang-off requires bare lower riser
n Provide input to operating procedures         n Soft soils improve LFJ and WH response
n Predict inspection requirements               n Retainer valves needed for disconnect
                                                n High VIV fatigue damage = increased
                                                  inspection and/or suppression




                                                                                                 2
                                                                                                                                          VORTEX INDUCED
     ANALYSIS LIMITATIONS
                                                                                                                                            VIBRATIONS
n   Only as good as input assumptions:                                                              n Still subject to research
    u Currents                                                                                      n Analysis methods relatively new
    u Drag coefficients                                                                             n Do VIV’s really happen?
n Uncertainty in effects of drill string tension                                                    n What are the effects?
n Requires margin of conservatism                                                                   n How good/bad are our predictions?
n Can be costly - VIV                                                                               n How are VIV’s best managed?




    VIV ANALYSIS METHODS                                                                                VIV ANALYSIS APPROACH
n   DnV Rules                                                                                       n Analyses conducted with several current
    u       Uniform risers in uniform, planar current                                                 profiles
n   SHEAR7                                                                                          n Current profiles of varying severity,
    u       Uniform top tensioned risers                                                              typically based on exceedence level
    u       Sheared, planar, monotonic current profile                                              n Fatigue damage factored according to
n   VIVA                                                                                              duration of profile
    u       Variable riser properties along the length                                              n More refined selection of profiles at more
                                                                                                      severe currents




                                      VIV FATIGUE                                                    VIV DRAG AMPLIFICATION
                                           VIV Damage Along Riser                                                                                      VIV Drag Amplification Factors
                                                                                                         Drag Amplification Factor




                         0.002                                                                                                           2.6
                                                                                                                                         2.4
        Fatigue Damage




                         0.0015                                                                                                          2.2
                                                                                                                                          2
                         0.001                                                                                                           1.8
                                                                                                                                         1.6
                                                                                                                                         1.4
                         0.0005
                                                                                                                                         1.2
                                                                                                                                          1
                             0                                                                                                           0.8
                                  0      0.2             0.4           0.6       0.8            1                                              0          0.2           0.4         0.6         0.8            1

                                          Location along Riser (x/L)                                                                                      Location along Riser (x/L)
                  0.2 m/s Current      0.4 m/s Current         0.6 m/s Current   0.8 m/s Current                                     0.2 m/s Current      0.4 m/s Current     0.6 m/s Current    0.8 m/s Current

                  1.0 m/s Current      1.2 m/s Current         1.4 m/s Current   Total Damage                                        1.0 m/s Current      1.2 m/s Current     1.4 m/s Current




                                                                                                                                                                                                                   3
                    VIV UNCERTAINTIES                                                                VIV - ACTUAL v PREDICTED
n Current profile and direction                                                                                   Current Profile                                        Riser Displacement
                                                                                                     400


n Slick and buoyant joints                                                                                                                                                     1

                                                                                                     350                                                                      0.9



n Choke and kill lines                                                                               300
                                                                                                                                                                              0.8

                                                                                                                                                                              0.7
                                                                                                     250




                                                                                    m above seabed
n Drill string tension                                                                                                                                                        0.6




                                                                                                                                                                        x/L
                                                                                                     200                                                                      0.5



n Damping of multi-string system                                                                     150
                                                                                                                                                                              0.4

                                                                                                                                                                              0.3



n Conductor interaction
                                                                                                     100
                                                                                                                                                                              0.2


                                                                                                     50                                                                       0.1

                                                                                                                                                                               0
                                                                                                         0                                                                          0    0.1     0.2       0.3     0.4   0.5
                                                                                                             0       0.2      0.4         0.6     0.8   1                                              RMS A/D
                                                                                                                                   Speed (m/s)

                                                                                                                           Observed Current                                                    Monitored Riser Displacement
                                                                                                                           Corrected Current                                                   SHEAR7 Riser Displacement




                                                                                                                                         MODELLING
           DRILL STRING TENSION
                                                                                                                                        UNCERTAINTIES
           1
                                                                                               0
                                                                                              40
                                                                                                                                                                   1
          0.9                                                                                  5
                                                                                              30
                                                                                                                                                                  0.9
          0.8
                                                                                               0
                                                                                              30                                                                  0.8
          0.7
                                                                              m above seabed




                                                                                                                                                                  0.7
                                                                                               5
                                                                                              20
          0.6
                                                                                                                                                                  0.6
                                                 No Drill String Tension                       0
                                                                                              20
    x/L




                                                                                                                                                            x/L

          0.5                                                                                                                                                     0.5
                                                 100te Drill String Tension
          0.4                                                                                  5
                                                                                              10                                                                  0.4

                                                                                                                                                                  0.3
          0.3                                                                                  0
                                                                                              10
                                                                                                                                                                  0.2
          0.2
                                                                                                     0
                                                                                                     5                                                            0.1
          0.1
                                                                                                                                                                   0
                                                                                                     0                                                                   0              0.2        0.4           0.6      0.8
           0
                0    0.2    0.4      0.6   0.8
                                                                                                         0        02
                                                                                                                   .         0.4        0.6      0.8    1                                          RMS A/D
                           RMS A/D
                                                                                                                               p e ms
                                                                                                                              S e d( / )




                IMPLICATIONS OF VIV                                                                                                            VIV FATIGUE
                      FATIGUE                                                                                                                 MANAGEMENT
n   Resistance:                                                                               n              Objectives
    u Change tension/buoyancy                                                                                    u Minimise conservatism
    u Higher quality fatigue details in riser and                                                                u Account for actual environment
      wellhead/conductor                                                                                         u Reduce modelling uncertainties
    u More frequent inspection                                                                n              Options
n   Suppression:                                                                                                 u Entirely predictive
    u Fairings - expensive but reduce drag                                                                       u Analysis predictions used in conjunction with
    u Strakes - cheaper but increase drag                                                                          measured environment
                                                                                                                 u Monitored environment and response




                                                                                                                                                                                                                                4
            ENTIRELY PREDICTIVE                                                                                                        PARTLY PREDICTIVE
                                          VIV Damage Along Riser                                                                                     VIV FATIGUE DAMAGE ACCUMULATION
                         0.002
                                                                                                                                      1.00E-02




                                                                                                        Fatigue Damage Per 12 Hours
        Fatigue Damage




                         0.0015                                                                                                       1.00E-03


                         0.001                                                                                                        1.00E-04


                                                                                                                                      1.00E-05
                         0.0005
                                                                                                                                      1.00E-06                                     Top Tension =
                             0                                                                                                                                                     700kips
                                  0     0.2             0.4           0.6       0.8            1                                      1.00E-07                                     Top Tension =
                                                                                                                                                                                   850kips
                                         Location along Riser (x/L)                                                                   1.00E-08
                  0.2 m/s Current     0.4 m/s Current         0.6 m/s Current   0.8 m/s Current                                                  0         0.5          1           1.5            2
                  1.0 m/s Current     1.2 m/s Current         1.4 m/s Current   Total Damage                                                               Surface Current Speed (m/s)




                                                                                                       RESPONSE MONITORING
                         MOSTLY MONITORED
                                                                                                           APPROACHES
n Stress or displacement amplitudes and                                                            n   On-Line System
  frequencies                                                                                          u                Hardwired
n Used with predictions to give fatigue                                                                                               F   Increased installation time, cable damage
  damage distribution over riser length                                                                u                Signal transmitted by telemetry
n Used with current measurements to                                                                                                   F   Large batteries, expensive
  calibrate predictions                                                                            n   Passive System
n Removes environmental and modelling                                                                  u                Run with riser, or ROV installed
  uncertainties                                                                                        u                Data processed after unit retrieval
                                                                                                       u                Low cost




                PASSIVE MONITORING
                                                                                                                                                     CONCLUSIONS
                     EXAMPLES
n   BP Schiehallion Drilling Riser                                                                 n Deep water presents many challenges
    u 360m water depth, 3 monitoring locations                                                     n AMJIG Guidelines needed to supplement
    u VIV up to mode 4 observed                                                                      existing codes
    u Response being evaluated                                                                     n VIV fatigue significant
n   NDP                                                                                                u Analysis may overestimate damage
    u 500-1400m, 5 monitoring locations                                                                u Inspection requirements based on analysis may
    u 3 Fields, Nyk High, Vema and Helland Hansen                                                        be overly conservative and costly
    u Small responses                                                                                  u Monitoring provides more rational approach to
                                                                                                         fatigue management




                                                                                                                                                                                                       5