Environmental analyses apart, off-shore oil and gas platform are remarkable constructions. While to the non-expert eye all platforms may look the same, there in fact several different types.
Here you have the most common.
This type of platform is used in shallow waters (100-150 meters max), and it's composed of several single and independent but interconnected platforms, each one with different functions such as extraction and refining.
The foundation of these structures is made of huge concrete pillars, which lay on the bottom of the seavwithout being fixed. Once a suitable surface is found, gravity will provide stability, thanks to the sheer weight of the pillars.
These are truly majestic engineering works as they lay on a steel tower, which is attached to the sea floor, up to 900 meters deep. They're called compliant because they can sway and follow the motion of the ocean. They are suitable for areas subject to hurricanes, such as the Gulf of Mexico for example.
For depths over 450 meters, the steel tower is usually supported by additional steel cables.
There are three types of floating platforms.
Floating Production, Storage and Offloading (FPSO) platforms basically consist of boats of other types of floating platforms.
They're used to store and produce oil and natural gas, and to collect oil from other nearby platforms. They are ideal for those areas where it's impossible or inconvenient to build an oil or gas pipeline for fuel transportation.
The second type of floating off-shore oil platform is the Tension Leg Platform (TLP), whose stability is provided by cables tethered to the seafloor, which can be up to 2000 meters deep.
Finally, the third type is called SPAR, which lays on a floating cylinder which is also it's also tethered to the bottom with cables. Depth can go from 300 to 3000 meters.
Over the years, Cividac deigned several components for off-shore oil and gas platforms. Designing such equipment has to take into account the very limited availability of space, which makes this type of project quite challenging.