gom offshore structures design criteria

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GoM Offshore StructuresDesign Criteria

SNAME Texas Section Meeting

Abdel Ghoneim and Craig Colby, DNV Houston

13 Dec 2005



Version Slide 213 December 2005

Agenda:

Fixed New/Existing Platform Criteria

Floating System Environmental Criteria

MODU Station Keeping Design Criteria

Mast / Derrick Foundation Criteria

Pipeline Design/Protection Criteria




Hurricanes Andrew 1992 & Katrina 2005

© MMS Assessment Workshop 9/23&24/03




Source: MMS




Offshore GoM: Hurricane Aftermath




Summary of Recent Hurricane Damage:

Ivan Katrina Rita

Platforms Destroyed 7 46 65

Platforms Severely Damaged 20 20 32

Rigs Destroyed (JU’s) 1 4 4

Rigs Severely Damaged 4 9 10

Rigs Adrift (Semi’s and JU’s) 5 6 13

Source: MMS




BP Ivan Platform Damage

Ivan Wave Observations: Pompano:

Observed damage to cable trays at EL (+) 63 ft.

3rd order stream function , 55% of wave above MSL

Estimated wave height = 105 ft assuming 6ft tide & surge.

Ultimate strength analyses correlate to Pompano surviving event.

Ivan Track at Virgo:

Observed damage to cable trays at EL (+) 70 ft. 3rd order stream function , 55% of wave above MSL

Estimated wave height = 116 ft assuming 6ft tide & surge.




API Offshore Structures Design Practice

API RP 2A 21st edition 2000. Fixed Jackets

- First created in 1969. Major Updates 9th Ed. 1978, 20th Ed. 1993

- Water depth limitation of critieria is 1000 ft linearly extrapolated from 400 ft.

- Specifies 100 year design criteria

API RP 2SK 2nd edition 1996 for Moored Station Keeping

- First edition in 1994

- Derived from

- API 2P in 1987 for mobile offshore units- API 2FP1 in 1993 for floating production systems

- Specifies 100 year design criteria for permanent systems

- Specifies 5 year or 10 year criteria for mobile systems

API RP 2T 2nd edition 1997

- First edition in 1987

- Specifies 100 year criteria

API RP 2FPS 1st Ed. 2001




API RP-2A Vintage

‘64 ‘69 ‘84 ‘92

1950 1960 1970 1980 1990

‘78 ‘93 ‘97

HildaFailures

CamilleFailures

Juan

Failures

(manned)

AndrewFailures

H u r r i c a n e s

API RP 2A

20th Edition

API RP 2A

1st Edition

API RP 2A

9th Edition

API RP 2A

19th Edition

API RP 2A

Supplement 1

Section 17

I n d

u s t r y

S t a n

d a r d s

D e s i g n

P

r a c t i c e

25- year to 100 -year

Criteria ?

Quality

Joint

Equations

Modern

Design

Code

Reassessment

Activities

(AIM)

Updated

Wave Load

Recipe

Existing

Platform

Assessment

MMS

Inspection

Program

Begins

Pre -RP 2A Early -

RP 2AModern -RP 2A

‘91‘8‘82‘82‘72‘72‘48‘48

‘64 ‘69 ‘84

1950 1960 1970 1980 1990

‘78 ‘93

HildaFailures

CamilleFailures

Juan

Failures

(manned)

AndrewFailures

H u r r i c a n e s

API RP 2A

20th Edition

API RP 2A

1st Edition

API RP 2A

9th Edition

API RP 2A

19th Edition

API RP 2A

Supplement 1

Section 17

I n d

u s t r y

S t a n

d a r d s

D e s i g n

P

r a c t i c e

25- year to 100 -year

Criteria ?

Quality

Joint

Equations

Modern

Design

Code

Reassessment

Activities

(AIM)

Updated

Wave Load

Recipe

Existing

Platform

Assessment

MMS

Inspection

Program

Begins

Pre -RP 2A Early -

RP 2AModern -RP 2A

‘91‘89‘82‘82‘72‘72‘48‘48

MMS Workshop Sept. 23-24, 2003

Pat O’Connor’s Presentation




API 2A 100 yr Criteria

API 21st Ed. Fig. 2.3.4-3




API RP-2A 20th Edition

1 10 100 1 .103

1 .104

20

40

60

80

100

120

Return Period (Years)

M o s t P r o b a b l e M a x i m u m W a v e H e i g h t ( f t )

Hm

Tr Hm( )OTC-7484 Petrauskas, et. al., 1994

For

MLLW= 400 ft




ISO/FDIS 19901-1 Final Draft 9/28/05




ISO API Comparison

GoM Design Criteria (ISO Includes Ivan)

Wind (mph): 10 minute 1 Hour

ISO 103 94

API 2A 101 92

Wave: Hmax (ft) Period (s)

ISO 85 14.9 Tp

API 2A 70.5 13 Tm




Load Nonlinearity

Jacket Wave Loading

0

1000

2000

3000

4000

5000

6000

7000

40 50 60 70 80

Wave Height (ft)

L a t e r a l F o r c e ( K i p )

MMS Dissemination Meeting 11/15/05 Frank Puskar Presentation




ISO Wind Design

500 1000 1500 2000 2500 3000 350040

45

50

55

60

65

Duration (s)

S p

e e d ( m / s )

Uzt t( )

t

3s Gust Local

5s b < 50m

15s b >= 50m

20s + Wave Dyns.

1 min+Wave Mod. Dyns.

1 h Neg. Dyns.

Duration DesignCond.




Comparison of Wind Speeds in Lili

MMS Study 469 by RTCI, October 2002




API 2SK and API 2T

No design criteria values specified.

Operators case by case specification.

- Deepstar generic criteria

Significant wave heights derived from GUMSHOE and well calibrated.

- Site specific vs. regional criteria

- Sensitivity of site location to historical storm tracks

- Must properly account for pooling of sites due to limited historical base

Hmax, Airgap Specification

Wind models

- More diverse models used in industry.

- Floaters more sensitive to wind force than fixed platform




DeepStar Metocean Criteria

Deepstar DSVI CTR 6401-5, July 2004




MODU Station Keeping Criteria

Floating MODUs

- Operator Requirements

- API 2SK Recommended Practices- IMO MODU Code

- Classification Society Rules

Jackup MODUs- Operator Requirements

- Marine Warranty Company Requirements

- SNAME

- IMO MODU Code

- Classification Society Rules




Hurricane Katrina




API RP 2SK

Current criteria

- 100-yr event for permanent, manned, or with restrictions

- 10-yr event for MOU’s in vicinity of other structures

- 5-yr event, otherwise

Upgrade from API 2P in 1987 which specified 99.9% non-exceedance (3 months) to the 5 and 10 years.

Requires one line damage criterion and a transient analysis whenoperating in close proximity of other structures

Studies have been commissioned by MMS and Industry (MMS JIP)

to review the experience during recent hurricanes and proposemodifications to reduce mooring failures and reduce damage tosubsea pilpelins




API RP 2T and RP 2FPS

2T:

- 100-yr criterion br referencing RP 2A.

- “The Largest Responses of TLP’s are not necessarily produced by the

highest wave conditions”- Four frequency bands of environmental loads identified:

1. Steady forces: Wind, Current and Wave drift

2. Low Frequency: 1-3 minutes sway, yaw, and surge

3. Wave Frequency: 5-20 s Member and Mooring forces4. High Frequency: 1-5 s

2FPS:

- 100-yr Ref. 2A for Category 1 (>5 year Dev.),- Lower return period for Cat 2 ( 60days-2 years), and Cat. 3 (<= 120 days).

- References 2SK and RCS for Cat.3.




IMO MODU Code and RCS

IMO MODU Code- Does not address floating units to any

significance

Classification Society Rules- DNV

- POSMOOR optional class notation – 100 year criteria DNV-OS-E301October 2004

- Extensive update and calibration- New POSMOOR, Drill Rigs, and

NMD- Main class requirements for

inspection of chain / wire every 5

years

- ABS- Refers to Owner’s (API RP’s)- Main class requirements do not

require inspection of chain




GOM Regulatory Requirements

USCG

- Compliance with IMO MODU code

- Does not cover station keeping

MMS- Operators/MODUs require MMS permit for drilling operations

- MMS has traditionally focused on API compliance if any invovlement

- Has no jurisdiction on stacked rigs

Nov 17th meeting called by DoI:

- Risk analysis assumptions

- Special performance requirements in deepwater

- Inspection requirements/schedule of mooring systems

- Securing platform rigs

- All L-1?




Derrick / Mast Design Criteria

Before Katrina After Katrina




API 4F Criteria

First published as 4E in 1970 with 3rd Edition in 1988. 4F 1st Ed. In1985 and 2nd Ed. In 1995.

Derricks are getting larger and larger using dual designs and drilling in

deeper waters and deeper wells.

Wind Criteria:

- 123 mph wind for derricks >140’ in height (107 mph w/ setback)

Wind force calculation methods- Draft for updated wind loading was never adopted since it was proposed

around 2000/2001.

Dynamic derricks account for platform motions. No dynamic effectsrelated to the installation response

No guidelines regarding modeling assumptions especially w.r.t. derrickfootings.

H i IVAN MMS S di




Hurricane IVAN – MMS Studies

SCR

PLATFORM (shallow water fixed) (Energo)

CONVENTIONAL RISER

PLATFORM (deepwater

Floater (seafastening, mooring) (OTRC)MODU stationkeeping (ORTC))

Mudslide effects (Lettis & OTRC)

Pipelines (DNV)

Hurricane IVAN: Sept 5, 2004

IVAN GOM production shut-in:

80% - week of Sept 12, 2004

30% - mid October, 2005

10% - early Jan 2005




Pipeline Damage – 180 reports Ivan & Mudslides

Damage causedistribution

Submerged

Pipeline

Departing Riser

Receiving Riser

Both Risers

Tie-in

pull apart

riser bent

line dented

line kinked

Unknow

line pulled up

line rupture

twisted/bent

other

Damages

Distribution by

pipeline Type 72

49

43

79

64

24

4

40

7

25

9 5

24 of these

damage reports

noted mudslides

as cause.

I d t F db k




Industry Feedback

Include recent hurricanes in the metocean database and updatecriteria accordingly

Problem of MODU’s set adrift by hurricanes is to be addressed

Assess the risks associted with design optimization

Derrick and Mast Specification.

- Often done by drillers

- Only specifies 4F compliance in derrick design

- Engineers with dynamics and motion background often not invovled

Tie Down Study

- MMS Ivan white paper by OTRC focusing on tie downs as weak link.

- Need for more rigorous guidelines/specs.

API OS SC2 R




API OS SC2 Response

Re-evaluate Standards

- RP 2A – Fixed Structures

- RP 2T – Tension Leg Platforms- SPEC 4F – Drilling and Well Servicing Structures

- RP 2SK – Station Keeping

Metocean Criteria

- Calculate GoM criteria using various area averaging models

- Update API GoM metocean criteria to reflect latest storm data

- Update ISO Metocean Regional Annex to include Katrina and Rita- Produce background guidance document for design engineers

R d M




Road Map:

Understanding levels of safety in standards

Including all hurricane exposures

Reducing future damage Significant differences between hindcast results

High risk of MODU’s going adrift and high potential consequences

Realistic calculation methods

Instrumentation and inspection of critical areas

Verification and certification Experience feedback and follow-up system

Cost sharing and incentives system




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