An earth quake on the bottom of the sea floor in the gulf creates fissures - water well drilling sometimes uses explosives to fracture a well bottom to create pockets to fill with water for pumping, if a similiar practice is used in oil gas well drilling, you would have frequent smaller man made earthquakes cracking lots of crust letting thousands of seemingly small cracks add up and merge and join hands.
If in the future such cracks all over the sea floor around the globe open signifigantly - suppose it would help the oceans become as the rotting blood spoken of here.
Revelation 16:3 And the second angel poured out his vial upon the sea; and it became as the blood of a dead man: and every living soul died in the sea.
As the supernatural curse descends out of the angel's container into the oceans, hydrogen sulfide, methyl chlorides, benzenes, crude oil sludge, and much more rise from the deep.
As blood sits at room temp, it seperates into solids and seperate liquid, the proteins clump together, the PH becomes lethal, it stinks, it looks nasty, it stains all it touches - and so on. Salt breaks the red blood cells and helps reliquify them - good to get blood off of scrubs and white lab coats, but an ocean full all around the globe.
Every living creature dies rapidly, no more algae / plankton making oxygen, eating carbon dioxide - soon the air changes and progresses. Only the presence of God - the Person symbolized by the Holy Oil will guard the life of the redeemed.