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Engineering LibreTexts

21: Oil Spills

  • Page ID
    12118
  • Learning Objectives

    After completing this chapter, you will be able to:

    1. Outline the most common causes of oil spills on land and at sea.
    2. Describe how spilled oil becomes dispersed in the environment.
    3. Explain how hydrocarbons cause toxicity to organisms.
    4. Explain how petroleum kills birds and how they may be rehabilitated.
    5. Describe case studies of the ecological effects of oil spills at sea and on land.
    6. Discuss the potential consequences of petroleum resource development in the Arctic.

    Introduction

    Petroleum (crude oil) is a non-renewable natural resource (Chapter 13) used mainly as a source of energy. It is also used to manufacture a diverse array of petrochemicals, including synthetic materials such as plastics. Petroleum is mined in huge quantities. Pipelines, ships, and trains transport most of this volume, plus its refined products, around the globe. The risks of spillage are always present, and oil spills may cause severe ecological damage. Petroleum accounts for about 33% of the global production of commercial energy (in 2013; 31% in Canada) (Table 13.9). Moreover, the global use of petroleum is still increasing – by 8% from 2004 to 2013 (Table 21.1). The fastest increases are in rapidly growing economies, such as China (59%) and India (75%). Relatively wealthy, developed countries support about 20% of the human population, but account for 48% of the global use of petroleum – 22% in North America, 21% in Europe, and 5% in Japan.

    Table 21.1. Petroleum Production and Use in Selected Countries in 2013. Data are in 106 t/year, with percentage change since 2004 (10-year period) given in brackets. Positive values for net export means the country produces more petroleum than it uses, so the rest is exported. Source: Data from British Petroleum (2015). table21_1.jpg

    The global reserves of petroleum are about 238-billion tonnes, of which 48% occurs in the Middle East, 13% in North America, and 6% in Russia (2013 data; BP, 2014). Almost all mining of petroleum occurs far from the places where it is consumed. The Middle East, for example, is a huge exporter of petroleum and its refined products; the amount shipped abroad is about 3.5 times larger than domestic usage in that region. In contrast, Europe (minus the former USSR) produces about 22% of the petroleum it consumes, while Asia produces 28%, and the United States 54%.

    Canada produces about 87% more petroleum than it consumes (in 2013; CAPP, 2014). About 42% of the production is conventional crude oil, and the other 58% is synthetic petroleum manufactured from oil-sand bitumen. About 76% of the Canadian production occurs in Alberta, 15% in Saskatchewan, and 7% offshore of Newfoundland.

    Most of the production occurs in remote areas, while most consumption is in densely populated areas of the country. Consequently, enormous quantities of petroleum and its refined products are transported over great distances, mostly by overland pipelines, railroads, and trucks. In addition, western Canada exports large amounts of petroleum and refined products to the United States and to Asia, and eastern Canada exports to the eastern United States and imports from the Middle East and Latin America. Therefore, even though Canada is more than self-sufficient in its net production and consumption of petroleum, immense quantities of the commodity and its refined products move within, out of, and into the country and its regions.

    On the global scale, most petroleum and its refined products are transported by oceanic tankers and overland pipelines. Local distribution systems involve smaller tankers, barges, pipelines, railroads, and trucks. There is a risk of accidental spillage from all of these means of transportation. Some of the spills have been spectacular in their volume and environmental damage. In addition, petroleum is discharged into the environment by many smaller sources, which sum to a large cumulative amount.

    In this chapter we examine the causes of oil spills and the ecological damage that can be caused in aquatic and terrestrial environments.

    Petroleum and Its Products

    Petroleum is a naturally occurring mixture of liquid organic compounds, almost all of which are hydrocarbons (molecules made up only of hydrogen and carbon atoms). Petroleum is a fossil fuel, as are coal, oil-sand (or bitumen-sand), and natural gas. Fossil fuels are derived from ancient plant biomass that became buried in deep sedimentary formations. Over geologically long periods of time, the biomass was subjected to high pressure, high temperature, and anoxia. The resulting chemical reactions eventually produced a rich mixture of gaseous, liquid, and solid compounds. Naturally occurring hydrocarbons range in complexity from gaseous methane, with a weight of only 16 g/mole, to solid substances in coal with molecular weights exceeding 20,000 g/mole. (In chemistry, a mole is a standard quantity of a substance, equivalent to the amount contained in 6.02 × 1023 atoms or molecules.)

    Hydrocarbons can be classified into the following three groups:

    • Aliphatic hydrocarbons are compounds in which the carbon atoms are organized in a simple chain. Saturated aliphatics (also called paraffins or alkanes) have a single bond between adjacent carbon atoms, while unsaturated molecules have one or more double or triple bonds. This is illustrated by the two-carbon aliphatic hydrocarbons ethane (H3C─CH3), ethylene (H2C═CH2), and acetylene (HC≡CH). Unsaturated aliphatics are relatively unstable and do not occur naturally in petroleum. Rather, they are produced during industrial refining, and photochemically in the environment after crude oil is spilled.
    • Alicyclic hydrocarbons have some or all of their carbon atoms arranged in a ring structure, which may be saturated or unsaturated. Cyclopropane (C3H6) is the simplest alicyclcic hydrocarbon.
    • Aromatic hydrocarbons contain one or more five- or six-carbon rings in their molecular structure. Benzene (C6H6) is the simplest aromatic hydrocarbons.

    Crude petroleums vary greatly in their specific mixtures of hydrocarbons and other chemicals. They typically consist of about 98% liquid hydrocarbons, 1-2% sulphur (or less), and < 1% nitrogen, plus vanadium and nickel up to 0.15%. When petroleum is processed in an industrial refinery, various hydrocarbon fractions are separated by distillation at different temperatures. This is done to produce such products as gasoline, kerosene, heating oil, jet fuel, lubricating oils, waxes, and residual fuel oil (also known as bunker fuel). In addition, a process known as catalytic cracking converts some of the heavier fractions into lighter, more valuable hydrocarbons such as those in gasoline.

    Oil Spills

    Oil pollution is caused by any spillage of petroleum or its refined products. The largest spills typically involve a discharge of petroleum or bunker fuel to the ocean from a disabled tanker or a drilling platform, to an inland waterway from a barge or ship, or to land or fresh water from a well blowout or broken pipeline. In addition, some enormous oil spills have resulted from deliberate acts of warfare.

    Terrestrial Spills

    Oil spills onto land are relatively common. Between 1989 and 1995, about 3,500 spills per year were reported in Canada – most all were relatively small, although by law they must be reported (Environment Canada, 1998). About 42% of the spills occurred in the vicinity of production wells, while 29% were from pipelines, and 16% from tanker trucks. During that period, up to 140-thousand t of oil was spilled per year in petroleum-producing areas, due to accidental losses and well blowouts. In another study of the period 2000 to 2011, a total of 1,047 spills were reported from oil or gas pipelines in Canada (Kheraj, 2013).

    Most large terrestrial spills involve a ruptured pipeline. Canada has about 36-thousand km of pipeline for transporting petroleum and refined liquids and 255-thousand km for natural gas (CAPP, 2014; for comparison, there are about 1.0-million kilometers of roads, of which 416-thousand are paved; Transport Canada, 2014). Pipeline breaks may be caused by faulty welding, corrosion, or pump malfunctions, as well as by erosion slumps earthquakes, and even armed vandals engaged in target practice. Operator negligence may also be an issue, as was the case of the Lake Mégantic disaster in 2013 (Canadian Focus 21.1).

    The extensive Canadian network of pipelines incorporates spill sensors and other advanced technologies that allow damaged sections to be rapidly shut down. When this system works well, it allows individual accidents to be kept relatively small. Some other countries use fewer of these technologies, and consequently may suffer huge petroleum spills from overland pipelines. For example, in northern Russia, some pipelines have become corroded, and insufficient countermeasures are in place to prevent or contain oil spills.

    In general, oil spilled on land affects relatively localized areas of terrain because most soils absorb petroleum well. However, much larger areas of aquatic habitat are affected if spilled oil reaches a watercourse, because wind and currents cause slicks to spread and disperse widely.

    Canadian Focus 21.1. Off the Rails at Lake Mégantic. Late one night in June, 2013, a train carrying a 72-car load of petroleum to a refinery in Saint John, NB derailed in the town of Lac-Mégantic, QC (Wikipedia, 2015). The train had actually passed through the town some hours previously, but had been parked 11 km further along for the night, but its conductor (the sole operator of the train), prior to going to a local hotel to sleep, did not set enough manual brakes to keep the train in place. When the brakes failed, the unattended train rolled backward, reaching a speed as fast as 100 km/hour, and eventually derailed in the downtown core of Lac-Mégantic.

    Because the cargo of light petroleum was so inflammable, 63 of the 72 tank cars caught fire and exploded as immense fireballs that destroyed 30 buildings, some of them historic, and caused the deaths of 47 people, most of whom were late-night patrons of a popular nightclub. Associated environmental damage included pollution of groundwater and a nearby river with petroleum residues, as well as air pollution from the smoky plumes. The financial losses were in the hundreds of millions of dollars. Aided by funds provided by the provincial and federal governments, as well as insurance monies, the town of Lac-Mégantic is rebuilding its downtown, but the trauma of this terrible accident will linger for many decades.

    Although Canada has a good safety record for transporting petroleum, natural gas, and other hazardous goods, there is always a risk of an accident happening. Such events most often occur because of a failure of infrastructure or equipment, but inattention and negligence can also be a cause. There are no good excuses for either of those reasons for tragic and dangerous outcomes when it comes to transporting dangerous materials.

    Marine Spills

    Petroleum spills into the world’s oceans currently amount to about 1.4-million tonnes/year (Figure 21.1). This is considerably less than the spillage that occurred in the 1970s and early 1980s, which was 3-6 million tonnes/year (Koons, 1984). In addition to petroleum spills, there is a large natural emission to the oceans of hydrocarbons not derived from petroleum. These chemicals are synthesized and released by phytoplankton, at an estimated 26-million tonnes/year. These huge biological releases contribute to the background concentration of hydrocarbons of about 1 ppb (1 µg/L) in seawater. The biogenic emissions are a natural contamination and do not result in known biological damage. There are also natural emissions from underwater seeps, which amount to about 0.6-million tonnes/year and may sometimes cause local ecological damage.

    Figure 21.1. Petroleum Inputs to the Oceans. The data are in 103 tonnes per year over the period 1988 to 2007. Sources: “Best estimate” data from National Academy of Sciences (2003) and GESAMP (2007).

    figure21_1.jpg