How deep is the sand under the ocean and what's underneath ? Do oil rig platform legs go into rock ?

Answer 1

First, oil rig platforms do not set on truly solid rock. They couldn't possibly because in most areas where fixed-platform oil rigs are located the sand and silt may be miles deep. Fixed platforms which rest on the seafloor are typically built on-shore and towed to sea while laying on their side. They are then sunk into an upright position. Pilings are driven through the legs of the platform to anchor it in position. The jackets also have large mud mats (flat sheets) on the bottom to prevent them from sinking into the sand or mud bottom. Here are some photos of pile drivers in action, setting a jacket offshore:
http://www.vulcanhammer.net/off/photos.php

The sediment that most oil platforms are located on is typically deposited by a large river delta. The oil production in the Gulf of Mexico is in the ancient river deltas of many rivers that flowed into the Gulf over the past 65 million years. In some places the sand and shale deposited has reached thicknesses of 5 miles or more. For example, the Mississippi River delta where New Orleans is located is about a four to five mile thick deposit of sand and shale overlying Upper Cretaceous chalk. At a certain depth, often over several thousand feet down, the unconsolidated sediment changes to consolidated rock. It would be impossible to anchor an oil rig on the consolidated rock because it is so deep.

Deep under these sand and shale sediments in the Gulf of Mexico are large bodies of salt. One of the deepest wells so far in the Gulf of Mexico was drilled to over 27,000 feet (over 5 miles), and was still encountering sedimentary rock.
http://cat.inist.fr/?aModele=afficheN&cpsidt=13773983

Answer 2

Ocean floor may also be mud. I have heard of piles being driven (I believe, but it was a long time ago) 80ft down to support platform legs.

Answer 3

the sediment is on top of rock and various depths and types .
yes oil rigs go into the bed and drill sometimes miles deep.
this site has understandable information from exploration to refining and more.. and good pictures
http://science.howstuffworks.com/oil-drilling1.htm


For cool ocean posters and long winded scientific explanations see:
http://www.ngdc.noaa.gov/mgg/image/crustageposter.jpg
http://www.ngdc.noaa.gov/mgg/image/sedthickimages.html

Answer 4

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Answer 5

not all ocean floor is sand...some of it is rock