Structural Design Considerations for an Ice Resistant Semi Submersible Drilling Rig

• Main Author: Jacobsen, Heidi
• Other Authors: Amdahl, Jørgen, Storheim, Martin, Pettersen, Erik
• Format: Master Thesis
• Language: English
• Published: NTNU 2014
• Subjects: Ingeniørvitenskap og IKT; Marin teknikk; Arctic; Kara Sea; Iceberg*
• Online Access: http://hdl.handle.net/11250/2445658

Arctic areas contain large oil and gas fields demanding robust drilling and field development solutions. Semi submersible drilling and completion rigs are highly used for the current operations. Operating while surrounded by ice is associated with large possible damages from ice impacts. In addition, the Arctic areas are characterized by long distances and harsh climate. As commercial drilling operations are planned in among others the Beaufort, Barents and Kara sea, these complex environments need evaluation of both financial and safety risks. The exact area of interest is to a low extent described in previous work, but many similarities can be drawn to ship collisions with iceberg. The structural design is mainly based on requirements from the DNV ship rules, and the relevant aspects in a collision are similar for both structures. The current ice load is conservatively assumed applied as pressure load. Plastic considerations of plate fields before and after stiffener collapse reveal a significant demand for higher resistance towards extreme loads. Assuming large damages, the corresponding repair and strengthening costs for the considered case are estimated. Repair actions may span over a long time period due to failure of components. Hence, drilling downtime may add a significant financial risk. Redesigning an existing structure to withstand ice loads involve numerous considerations. The pontoon skin stiffeners are seen as most prone to failure. A possible reinforcement to increase the failure capacity is stated to illustrate its effect on the impacted plate field.