Now Shooting of our hips...are we ??..ehh
First of all in Gulf of Mexico-
Natural gas present under the crude oil deposit is under considerable pressure. That is why it is pushing the oil out. No oil will be transported in this gas pipeline.
lets say pressure in 36 inch gas pipeline in 1500 Psi(approx 103 bar
), pressure at 3km depth will be around 300 bar. So instead of gas coming out of the line , water will be entering the pipeline...so where is the damage to the marine environment.
For background reading
New Page 1
http://www-static.shell.com/static/irl/downloads/about_shell/safety_brochure.pdf