The Arctic region contains one of the largest oil and gas reserves in the world. However, the harsh and unpredictable environment poses extreme challenges to drilling and exploration operations in the region. Cold temperatures coupled with sea icing result in limited uptime for various offshore activities. In addition, constant threat from icebergs may require moored mobile offshore drilling units (MODUs) to be equipped with quick-release mooring systems in order to disconnect and move out of harm's way (Newfoundland Offshore Petroleum Installations Regulations, SOR/95-104).While a lot of attention has focused on MODU mooring design criteria in the Gulf of Mexico in light of recent hurricanes (Petruska et al. 2007), such criteria are not properly defined for Arctic regions. This paper addresses critical aspects for mooring design in the Arctic, particularly extreme temperatures (typically below 0°C) and icing that are not emphasized in current mooring design codes (API-RP-2SK, DNVGL-OS-E301). Typically, mooring designers assume air density of 1.225kg/m3 for computing wind loads, which corresponds to 15°C air temperature. The Arctic environment, on the other hand, characteristically has cold, relatively dry air coupled with strong winds. In such conditions, air density is much higher, thereby increasing the wind load on the MODU. Icing on the superstructure may further increase the wind load due to increase in projected wind area. These two effects (air density and icing) may increase the net wind load on the MODU by around 10–15% depending upon the ambient conditions. It is therefore important to apply correct physics for MODU mooring design in the Arctic. The paper also provides commentary on reasonable ways to combine the design storm condition (typically 100-year) with extreme temperatures in order to reduce conservatism in design, while allowing safe and robust operation.
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MODU Mooring Design Considerations in the Arctic Environment
Paper presented at the SNAME 21st Offshore Symposium, Houston, Texas, February 2016.
Paper Number: SNAME-TOS-2016-011
Published: February 16 2016
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Singhal, Gaurav, Cheng, Jun, Croston, Antony, and Alan Whooley. "MODU Mooring Design Considerations in the Arctic Environment." Paper presented at the SNAME 21st Offshore Symposium, Houston, Texas, February 2016.
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