Prevalence during Drilling versus Transportation
Offshore oil spills or leaks may occur during various stages of well drilling or workover and repair operations. These stages can occur while oil is being produced from offshore wells, handled, and temporarily stored; or when oil is being transported offshore, either by flowline, underwater pipeline, or tanker. Of the approximately 706 million gallons of waste oil in the ocean each year, offshore drilling operations contribute about 2.1 percent, and transportation accidents (both ships and tankers) account for another 5.2 percent. The amount of oil spilled or leaked during offshore production operations is relatively insignificant.
Oil waste from offshore drilling operations may come from disposal of oil-based drilling fluid wastes, deck runoff water, flowline and pipeline leaks, or well failures or blowouts. Disposal of offshore production waste can also pollute the ocean, as can deck runoff water, leaking storage tanks, flowline and pipeline leaks, and the wells themselves. Oil spilled from ships and tankers includes the transportation fuel used by the vessels themselves or their cargos, such as crude oil, fuel oil, or heating oil.