Ice Management. K. J. Eik StatoilHydro Research Centre / NTNU, Trondheim, Norway

Transcription

1 Gamle Logen, Oslo The 4rd Norway - Russia Arctic Offshore Workshop Ice Management K. J. Eik StatoilHydro Research Centre / NTNU, Trondheim, Norway

2 2 Content Definition of Ice Management (IM) IM activities IM experiences Arctic projects Learning's Efficiency of IM Event tree philosophy Icebergs Event tree philosophy Ice Ridges Summary

3 3 Definition of Ice Management Ice management is the sum of all activities where the objective is to reduce or avoid actions from any kind of ice features. This will include, both is not limited by: Detection, tracking and forecasting of sea ice, ice ridges and icebergs Threat evaluation Physical ice management such as ice breaking and iceberg towing Procedures for disconnection of offshore structures applied in search for or production of hydrocarbons

4 4 Technology for detection and tracking Satellites Synthetic Aperture Radars (SAR) Optical Aeroplane recognosaince Unmanned Air Vehicles (UAV) Marine Radars Visual observations Sonars and Autonomeus Underwater Vehicles (AUV) Gavia AUV (ref. R. Yeo, Hafmynd, Iceland)

5 5 Technology ice forecasting Ice and iceberg drift forecasting requires information from: Atmospheric models (wind, waves, air temperature) Oceanographic models (currents, sea temperature) Ice models (ice coverage, thickness, concentration, ice drift speed, ridging)

6 6 Threat Evaluation From Wright, 2000, PERD report 25-44

7 7 Physical Ice Management Occurence of sea ice, ice ridges etc. Ice breakers Azimuth propellers Barriers Icebergs Line or net towing Propeller washing Water cannon deflection

8 8 Grand Banks Iceberg Management Prototype methods (Crocker et al., 1998)

9 9 Beaufort Sea CANMAR Drillships ( ) North Sea experience Reinforced to Baltic class 1a super Seasonal drilling; 110 days pr year Vessels and support system staying idle in 8-9 months pr year

10 10 Beaufort Sea Kulluk ( ) Motivated by the shortcomings of the drill vessels Operation in 20m 60m water depth Typically 200 days in operation per year Environmental monitoring, physical ice management and ice alert procedures were extensively used.

11 11 Beaufort Sea Kulluk 44.7 down days in 585 operating days (92% operability) 8 moves off location 1 incident reported when Kulluk was pushed of location due to impact from a heavily ridged multi year ice floe (5kmx8km, 0.6 m/s) Effect of ice management Low ice concentration thin ice (0.5m): 65% reduction in mooring loads High concentration thin ice (0.5m): Nearly no reduction in loads Low concentration thick ice (2m): 75% reduction in loads High concentration thick ice (2m): 40% reduction in loads

12 12 Grand Banks Hibernia, Terra Nova, White Rose ++ Oil production from 1997 Water depths 80 m 120 m Icebergs 3 of 4 years Sea ice 1 of 5 years Icebergs in Sea ice in 1 of 6 years

13 13 Grand Banks Correlation between iceberg management success and Iceberg size No significant correlation, icebergs more than 5 million tons have been successfully towed Iceberg shape Slightly more difficult to deflect domed shaped and wedge shaped icebergs Sea state No correlation for sea states up to 5 m Hs Vessel experience

14 14 Barents Sea Experiment with iceberg towing in sea ice tons iceberg surrounded by 10/10 slightly deformed 0.5 m thick first year ice identified for towing Single line tow approach attempted Tow vessel unsteerable during tow and headed into the sea ice instead of the nearby polynea as planned Tow rope rupture due to uneven loads in towline and damage caused by sharp parts of the iceberg

15 15 Sakhalin Seasonal oil production at Sakhalin 2 from 1999 Production from June to December ice management systems applied during the ice break up and freeze up periods Many similarities with ice management in the Beaufort Sea Long T-time to lower the SALM safely to the seafloor (36 48 hours) Use of Azimuth icebreakers increase operation time with a few weeks in each end of the season

16 16 Learning s Exploration and/or production drilling have been performed successfully in a wide range of Arctic conditions Comprehensive use of ice management considered a key factor for the success Technology for iceberg handling is proven in open water not in ice covered waters It is recommended that ice management possibilities is highlighted at an early stage in the design process Challenge: How can the effect of ice management systems be incorporated in design of offshore structures?

17 17 Event tree approach (Industrial systems reliability) Starts with in initiating event Occurrence of iceberg within a certain distance from installation Occurrence of ice ridge Occurrence of multi year ice Include probability of failure of all safety systems Probability of unsuccessful detection Probability of unsuccessful iceberg towing Probability of unsuccessful ice breaking Probability of unsuccessful shut down procedures Probability of unsuccessful escape from site +++ Results in a number of different outcomes, all with a certain probability of occurrence.

18 18 Event tree approach - icebergs Initiating event Not detected by marine radar/satelite Iceberg drifts into structure Not able to tow iceberg in time Not able to escape location in time Not able to suspend operations in time Outcome Frequency (per year) True 0.29 True 0.01 False 0.99 Impact, pollution and lost production No impact, no pollution, no loss of production 2.9E E-02 Occurence of iceberg less than 10 nm from installation True 0.03 True per year False True False True False False False 0.99 Impact, pollution and lost production Impact, no pollution, loss of production No impact, no pollution, loss of production No impact, no pollution, no production loss No impact, no pollution, no loss of production 1.3E E E E E E-04

19 19 Event tree approach ice ridges Initiating event Max Annual Load > Resistance Not able to disconnect and escape location in time Not able to suspend operations in time Outcome Frequency (per year) Occurence of FY ice ridges in the region 0.15 per year True Damage to installation, pollution, 4.50E and loss of production 2.25E-05 True 4.50E E-07 True False Damage to installation and loss 1.46E No icebreakers 0.97 of production but no pollution 7.28E One icebreaker 1.46E Two Icebreakers 1.46E Three icebreakers False No damage to installation, no 1.35E pollution, but loss of production 6.75E E E-04 False No damage to installation, no 1.35E No icebreakers pollution, no loss of production 1.43E One icebreaker 1.49E Two Icebreakers 1.50E Three icebreakers One icebreaker 7.50E-04

20 Reduction in ice loads 20

21 21 SUMMARY Ice management considerations need to be included at an early stage in design of both operations as well as installations. Design loads may be reduced by including ice management in the design process. Existing design codes do not provide clear recommendations regarding how to include effects of IM. ISO opens for the possibility to benefit from IM capabilities in design Ongoing work will strongly benefit from access to previous collected data regarding ice breaker efficiency