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, 201015 yr by Externet
Added link

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.

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.

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