Offshore drilling operations create various forms of pollution that have considerable negative effects on marine and other wildlife.
These include drilling muds, brine wastes, deck runoff water and flowline and pipeline leaks. Catastrophic spills and blowouts are also a threat from offshore drilling operations. These operations also pose a threat to human health, especially to oil platform workers themselves.
Drilling muds and produced water are disposed of daily by offshore rigs. Offshore rigs can dump tons of drilling fluid, metal cuttings, including toxic metals, such as lead chromium and mercury, as well as carcinogens, such as benzene, into the ocean.
Drilling muds are used for the lubrication and cooling of the drill bit and pipe. The muds also remove the cuttings that come from the bottom of the oil well and help prevent blowouts by acting as a sealant. There are different types of drilling muds used in oil drilling operations, but all release toxic chemicals that can affect marine life. One drilling platform normally drills between seventy and one hundred wells and discharges more than 90,000 metric tons of drilling fluids and metal cuttings into the ocean.
Produced water is fluid trapped underground and brought up with oil and gas. It makes up about 20 percent of the waste associated with offshore drilling. Produced waters usually have an oil content of 30 to 40 parts per million. As a result, the nearly 2 billion gallons of produced water released into the Cook Inlet in Alaska each year contain about 70,000 gallons of oil.
Factors other than pollutants can affect marine wildlife as well. Exploration for offshore oil involves firing air guns which send a strong shock across the seabed that can decrease fish catch, damage the hearing capacity of various marine species and may lead to marine mammal strandings.
More drilling muds and fluids are discharged into the ocean during exploratory drilling than in developmental drilling because exploratory wells are generally deeper, drilled slower and are larger in diameter. The drilling waste, including metal cuttings, from exploratory drilling are generally dumped in the ocean, rather than being brought back up to the platform.
Offshore oil rigs may also attract seabirds at night due to their lighting and flaring and because fish aggregate near them. Bird mortality has been associated with physical collisions with the rigs, as well as incineration by the flare and oil from leaks. This process of flaring involves the burning off of fossil fuels which produces black carbon.
Black carbon contributes to climate change as it is a potent warmer both in the atmosphere and when deposited on snow and ice. Drilling activity around oil rigs is suspected of contributing to elevated levels of mercury in Gulf of Mexico fish.