Deep sea petroleum rigs...

[Externet]

How massive has the support legs/columns have to be on a mile deep ocean to support the facilities platform and rough seas ?

This is four times the world trade center building height

 

On its collapse, the sea floor would be a unbelievable maze of twisted steel beams; or how does the anchoring works, is it floating with many anchors around ?

 

Did the fire in the gulf sank the platform and collapsed the support towers?

 

http://www.bp.com/genericarticle.do?categoryId=9013609&contentId=7021443

Edited May 12, 2010 by Externet
Added link

[Ophiolite]

The well was being drilled with a floating semisubmersible rig, so no structure was required to support it. Production from these water depths is carried out using a TLP (Tension Leg Platforms) which are floating facilities held in place by multiple mooring lines. Here is an example whereby Shell set a record for the deepest water production facility.

[CaptainPanic]

The Troll platform was the tallest structure ever moved by man (according to wikipedia) at 472 meters.

 

A mile is too much.

I assume that you are referring to the Deepwater Horizon oil spill in the Gulf of Mexico?

As Ophiolite said, it was floating. However, I believe (and wikipedia agrees with me) that the platform was dynamically positioned... meaning that it was held in place by constant measurements and adjustments, not by lines.

 

I think that mooring lines of several miles long can be unreliable, and may also stretch too much to be of use. The last remark is pure speculation though.

[Double K]

Theres some good footage and images about Troll at the following link.

I saw this documentary just the other night, it's an amazing structure.

 

http://channel.nationalgeographic.com/series/engineering-connections/3334/Photos#tab-Videos/05318_00