Changing Practice in Gulf of Mexico Design and Operating Criteria - PowerPoint PPT Presentation

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Changing Practice in Gulf of Mexico Design and Operating Criteria

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  1. Changing Practice in Gulf of Mexico Design and Operating Criteria

  2. The Early Days(sometimes it is better to be lucky than good) • Gulf of Mexico platforms built around 1946 – 48 typically had deck heights 20 to 40 feet above mean sea level • Consultants’ evaluations: • “in 100 feet of water waves will probably seldom, IF EVER, exceed 20 feet in height” • “ … settled on a maximum wave height of about 25 feet and a recommended deck height of 32 feet” • Consensus: maximum wave ~ 29 feet, occurring perhaps once every 40 to 50 years. • Very loose “consensus” – no API guidance, little regulation.

  3. Luck Starts to Run Out • 1947 – 1952: series of relatively weak, small hurricanes in the Gulf • October 1949 – platform off Freeport damaged – post-mortem suggested waves as high as 40 feet. • Observed damage in others led to estimates of 22-29 feet – calls into question both the upper limit and frequency of occurrence of high waves in Gulf • Leads to stronger designs for a few operators

  4. Lulled to Sleep?All Hurricanes and Trop Storms in Gulf 1947 - 1955

  5. Luck Starts to Run Out • 1956 – Hurricane Flossie • A Category 1 storm • 50 men rode out the storm in the Gulf. One vessel lost its anchor and floated around during the storm in keeping with a philosophy of “taking a calculated risk that they would be safe.” • Led to calls for complete evacuation in hurricanes.

  6. Luck Starts to Run Out • 1957 – Hurricane Audrey • Forms in Gulf – now called “Sudden storms” • One mobile drilling rig sank, with four tenders suffering damage when pulled loose from their mooring and running aground • Industry record of no fatalities held.

  7. Industry Intensifies Action • 1957 – Hurricanes Audrey and Bertha – three significant storms in 2 years. • API forms “Advisory Committee on Fundamental Research on Weather Forecasting.” • Disbanded in 1962. • Why? Other issues and Gulf fairly quiet (Carla in 1961 but it hits Texas)

  8. Hmmmm?All Hurricanes and Trop Storms in Gulf 1956 - 1963

  9. No Consensus • Deck height practices: • Varied from the 1950 era standard of 28 – 32 feet above mean Gulf level to higher than 50 feet. • Not coincidently, those using higher values were companies directly impacted by storms either in terms of property or direct threat to employees. • Higher meant safer and more expensive – “each company placed a bet on the right combination of safety and cost”. (Primitive cost-benefit analysis)

  10. Luck Starts to Run Out All Hurricanes and Trop Storms in Gulf 1964 - 1973

  11. Luck Run Outs 1964 - 1969 1964: Hurricane Hilda – Category 4 • 1965: Hurricane Betsy

  12. Luck Runs Out 1964 - 1969 • 1964: Hurricane Hilda – Category 4 • Hilda was the most damaging tropical cyclone to the offshore oil industry, at the time of its impact. • More than US$100 million in losses. • 13 oil platforms were destroyed • 5 more damaged beyond repair[

  13. Luck Runs Out 1964 - 1969 • 1965: Hurricane Betsy – strong Category 3 at landfall • Eight offshore oil platforms were destroyed during Betsy, with others experiencing damage. • The oil rig Maverick disappeared during the cyclone

  14. Industry Action • 1966: API Committee on Standardization of Offshore Structures created. • Focus to create better design standards through cooperative efforts. • Basic research and measurement of wind, waves, and soils continues. • Includes the Ocean Data Gathering Program (ODGP) – 6 platforms instrumented in Gulf from 1968 through 1971

  15. Some “Good Luck”, Some Bad • 1969: Hurricane Camille ODGP measured a wave between 70 and 75 feet high!!!

  16. Some “Good Luck”, Some Bad • 1969: Hurricane Camille Used to calibrate hindcast models in Gulf for decades. Metocean criteria developed using those hindcasts as database of storms in Gulf. ODGP measured a wave between 70 and 75 feet high!!!

  17. API Standards and Design Waves • First API offshore standard (RP2A) issued in 1969 • No design wave information until 7th edition in 1976. • Recommends use of “the 100-year wave” • To this point the owner chose the return period and the use of both 25 and 100 year values was common. • 1% risk of exceedance annually = 100 yr • 4% risk of exceedance annually = 25 yr

  18. API Standards and Design Waves • 20th edition (1993) includes a new wave force calculation “recipe” that substantially changes that of the 19th edition (1991) • Design (“100-year”) wave conditions changed as well

  19. WOW! • 1992 saw Hurricane Andrew

  20. What Hath Andrew Wrought? • Category 4 storm in Gulf • MMS estimates 700 structures took “significant” hit • 22 older platforms destroyed • 65 others with significant damage • Majority had been designed to 25 year values and 35 to 40 foot decks • Newer platforms that were designed with decks to pass up to 72 foot waves had only minor damage

  21. Effect of Andrew and New API Force Recipe • Gave a boost of energy to an API committee looking at assessment of existing platforms • Task group decided that the new criteria should be relaxed for existing platforms and consideration be given to CONSEQUENCE OF FAILURE • Willing to take higher risks with older assets in part because cost to modify/replace are too high

  22. Effect of Andrew and New API Force Recipe • Three categories with different metocean criteria: • L-1 (high consequence / manned-evacuated or unmanned • Full-population of hurricanes, 1% annual exceedance probability • L-2 (low consequence / manned-evacuated) • Sudden hurricane and winter storm population • L-3 (low sequence / unmanned, or minimum consequence • Winter storm population • Included deck height criteria

  23. Consequence-based Criteria for New-Build Platforms • CBC for assessing existing platforms in place in 1996 (issued as a supplement to the 20th edition of RP2A. • Sets stage for introducing this concept for new-build • L1 • L2 • L3

  24. Lulled to Sleep Again?All Hurricanes and Trop Storms in Gulf 1993 - 2000

  25. What’s Happening Out There?All Hurricanes and Trop Storms in Gulf 2001 - 2005

  26. Impact of Ivan, Katrina, and Rita

  27. Impact of Ivan, Katrina, and Rita • 2005 Atlantic Season: most active in recorded history • 28 named storms, 15 hurricanes, 7 major hurricanes, and four category 5 hurricanes (per NOAA NHC) • Worst season previously: 1933 with 21 named storms, 10 hurricanes, and 5 major hurricanes

  28. Impact of Ivan, Katrina, and Rita • 2004-2005 was worst two year period (23 hurricanes) since 1886-1887 (21 total) • Lots of damage to platforms and mobile rigs (114 platforms destroyed in Katrina and Rita) • Lots of infrastructure damage (pipelines) leading to loss of oil and gas production

  29. MODU Failures – Floating (Semi) and Jackup Ivan, Katrina, and Rita

  30. API Metocean Reaction • Study of Ivan led to conclusion it was a rare event statistically but no need for significant criteria revision (OTC Paper 17740) • Recommendation was to simply include Ivan in any extremal analysis • Maximum Hs (m): • Ivan 16.0 • Katrina 16.9 • Rita 11.5 API Criteria before these storms? Hmax = 21.5 m Hs ≈ 12.6 m

  31. Industry and API Metocean Reaction • The rapid-fire occurrence of three huge storms in two years led to significant revisions in part due to a mooring risk JIP led by ABS which required the best possible metocean data • Several key findings: • Loop current and or Loop eddies provided get source of energy for all three of these storms • Dividing the Gulf into four regions was deemed appropriate • Use of the full 1990 – present hurricane database was not appropriate

  32. Other Areas Loop and Eddy Areas 10° 20° 30° 40° 0 -100 Depth below Ocean surface, m -200 -300 -400 Temperature, deg C Loop Current - Source of Deep Warm Water • Stages develop on time scale of months = persistent warm water conditions

  33. Storm Tracks over Loop Reprinted courtesy of Colorado Center for Aerodynamics Research

  34. API Metocean Criteria Changes after Ivan, Katrina, and Rita Gulf divided into 4 regions. Occasional Loop Random Eddies “Eddy Graveyard” Frequent Loop

  35. Bias in Storms Prior to 1950 • Measurements were sparse, often only at land stations. What went on in the Gulf was speculative. • In a 2006 paper (OTC 18418), Cooper and Stear concluded that there was a negative bias in the 1900 to 1949 storms as characterized by the National Hurricane Center.

  36. Bias in Storms Prior to 1950 Plots provided by Chevron Energy Technology Company • Plots: • 6 pre-’50; 16 post-’50 storms • Pre-’50, 70% of storms show no drop as they near coast • Post-’55, 12% show no drop • Suggest: pre-’50 applied coastal data offshore resulting in low bias • Other factors support conclusion: • NOAA generally does not use pre-’50 • 8 of top 10 winds occurred post-’50 • 7 of top 10 waves occurred post-’50

  37. Hurricane Reconnaissance Became common after WWII

  38. Industry Response • API RPs 2I, 2SM, and 2SK were all updated • MODU Mooring JIP (budget approx. $2.2m) Interim Guidance for Design of Offshore Structures for Hurricane Conditions API BULLETIN 2INT–DG First Edition, May 2007 Interim Guidance for Assessment of Existing Offshore Structures for Hurricane Conditions API BULLETIN 2INT–EX First Edition, May 2007 Interim Guidance on Hurricane Conditions in the Gulf of Mexico API BULLETIN 2INT–MET First Edition, May 2007

  39. Measured Data is Foundational • Hindcasts are used to generate criteria BUT these are calibrated against data Excellent network of data buoy in Gulf and along coast

  40. Future Hurricanes • More/less? • Stronger? • Similar tracks? • Was the 2004-2005 season a precursor of things to come?

  41. Future Hurricanes • Atlantic Hurricane Variability Over Time: 1886 – 2004 • Multi-decadal variability • El Nino Yellow = named storms, Green = hurricanes, Red = Category 3 and above

  42. Future Hurricanes • Was the 2004-2005 season a precursor of things to come? Was it all that unusual? • How confident can we be in the historical record? • Prior to about 1950 – no air reconnaissance • Satellites much later

  43. Future Hurricanes • Key factors: warm water and wind shear generally considered most important • Area of much current research AND considerable controversy • “Experts” do not agree • Models do not agree

  44. Two interpretations of SST data lead to VASTLY different future Atlantic activity extrapolated into the 21st century using absolute SSTs calculated from global climate model projections suggest that it is the SST in the tropical Atlantic main development regionrelative to the tropical mean SST that controls fluctuations in Atlantic hurricane activity Science 31 October 2008:Vol. 322. no. 5902, pp. 687 - 689DOI: 10.1126/science.1164396 CLIMATE CHANGE:Whither Hurricane Activity? Gabriel A. Vecchi,1 Kyle L. Swanson,2 Brian J. Soden3

  45. Future Hurricanes and API • As opposed to the general historical pattern of API, being REACTIVE, there is a shift to being more PROACTIVE • Funding a synthetic hurricane study at a cost significantly larger than “normal” API-funded research to develop a long term (100000 yrs) synthetic data base of hurricanes in the Gulf • Supportive of National Center for Atmospheric Research (NCAR) modelling work on how climate change is likely to influence hurricane activity through 2055 through RPSEA with Industry reps on steering committee, members’ time, etc.

  46. Future Hurricanes and API • No criteria changes to account for any future climate scenario being applied in part due to uncertainties • May be applied when the results of the sponsored research efforts are finished


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