Well, that's
kind of how the oil got there in the first place, except it was plant mass/algae in marshes sinking down I believe.
But we have ways we could yank it out of the atmosphere and sequester it; if we dedicated resources to it. Algae and
Photosynthetic Bacteria can process CO2 at speeds that put plants to shame, several times greater than even Sugar Cane (Which uses a ton of carbon, I believe, in its Calvin Cycle to make sugar.). That's why they are typically what's used to try and make efficient bio-fuels. You could grow massive batches of Algae, then sink them somewhere deep.
I seem to recall people talking about how fracked shale could contain carbon well, and the system to put it there is already in place. I wonder if you could shoot Algae down into there, heh.