We’ve discussed about two type of fixed platform structures which are piled offshore platforms and concrete gravity structures. In this article, it summarize the comparison between these two fixed offshore structures.
Figure 1 – Piled Structure and Gravity Structure of Brent (Courtesy of Shell UK)
Piled Platform Structures
Example of Pile Platforms – North Sea Valhall Field Platforms
- Horizontal stability is more reliable, allowing for a more economic design
- The final selection of the platform location is more flexible because the pile design is flexible to different soil conditions, and the pile can be modified even at a very late stage
- Material and fabrication costs are generally lower
- Site soil investigations can be less extensive, and costs therefore lower, so long as the decision to select a piled structure is made early on
- No need for a deep-water construction site
- Fabrication skills are mainly linked with steel working, meaning workers are easily available in shipbuilding areas
- Attaching pipeline risers to a steel structure is a simple procedure, and additional risers can be installed even after the structure is placed offshore
- When the site is abandoned, considerable work needs to be done to fully clear the area of debris, which adds cost at the end of the life of the platform.
Concrete Gravity Platform
Concrete Gravity Platforms
- Short installation times reduce cost, as well as exposure to weather risks
- Can potentially transport all deck and facilities to the offshore location after installation inshore, although this has rarely been carried out
- Capacity for oil storage on the platform
- Larger deck space can be provided
- Difficult to retrofit additional riser, as well as any other such alterations
- Construction is more reliant on unskilled labor, meaning workers will be more readily available for the project. However, construction sites need deep-water close to the shore, which will likely mean the construction site will be far from typical construction and industrial areas
- In theory, the structure can be de-ballasted and floated away at the end of its life, reducing the cost of abandonment, although this is yet to be put into practice.
References
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Energy-pedia. (2015) Norway: BP starts production from new Valhall platform in Norwegian north sea. Available at: http://www.energy-pedia.com/news/norway/new-153239 (Accessed: 22 January 2017).
Indian Maritime, Visakhapatnam and Indian Maritime University (2015) Sayan Bhattacharya. Available at: http://www.slideshare.net/ABHISHEKKUMAR790/introduction-to-offshore-structure-2 (Accessed: 22 January 2017).
PetroWiki (2013) Piled Offshore Structure. Available at: http://petrowiki.org/File%3AVol3_Page_537_Image_0001.png (Accessed: 22 January 2017).
Shell UK (2012) Brent Field Platonisms Available at: http://www.shell.co.uk/sustainability/decommissioning/brent-field-decommissioning/the-brent-story/_jcr_content/par/gallery/mediaplayer/image.img.800.jpeg/1480930096328/brent-field-cgi-highres.jpeg (Accessed: 22 January 2017).
Kaushik (2013) Troll-A platform: Largest object ever moved by man. Available at: http://www.amusingplanet.com/2013/03/troll-platform-largest-object-ever.html (Accessed: 25 January 2017).