Crude

The existence of oil has been known for centuries, since there are many natural seeps in the world. The LaBrea tar pit in California is an example of a natural seep. Early use included sealing seaworthy vessels, but demand was minimal until the development of the combustion engine. The growth in demand for gasoline and diesel has driven the exploration, production, and refining of crude oil.

As a fuel, the combustion is an instantaneous oxidation process that then releases heat and greenhouse gases. These greenhouse gases, stored for millions of years, are now being released at an alarming rate. Crude oil was forming and accumulating beginning about 600,000 million years ago. The first major oil company, Standard Oil, was founded in 1870. If it is assumed that global oil reserves will last another 100 years, then the entire recoverable deposits of oil will have been consumed in less than 250 years. So, in a fraction of the history of the Earth, millions of years of stored heat and gas are being released to the atmosphere. Oil is just one of the fossil fuels that have contributed to the greenhouse gas inventory. Natural gas and coal also contribute.

The standard unit of measure for oil is a barrel, which contains 42 gallons. Within a barrel of oil are many different hydrocarbon chains, and although a liquid, a barrel of oil can also contain gases and solids at certain temperatures. Hydrocarbons are molecules of hydrogen and carbon atoms in many different combinations. The longer the chain, the greater the weight, and the greater the number of carbon atoms. The lighter hydrocarbon molecules are the gases, such as methane and ethane. The heavier molecules in oil are known as bitumen or tar. In essence, the heavier the hydrocarbon, the greater the potential greenhouse gas emission, because it is a function of available carbon atoms. However, tar and asphalt are not intentionally burned, but their use as paving and roofing materials also contributes because radiated heat is then trapped by the greenhouse gas effect.

The reserve (supply) of oil is finite, but the amount left in the world to produce is uncertain, and to some degree is dependent on commodity price. There will be new discoveries where oil flows or is pumped in what is known as primary production. There will also continue to be production from old fields through enhanced oil recovery methods. Enhanced oil recovery involves some type of stimulation, usually through improved production technology, that is applied to old fields "squeezing" additional oil out of reservoirs. Increasing price justifies more squeezing and the development of new techniques to recover even more oil. However, at some point in the future, the world annual production will begin to decline. There is more oil being produced today through enhanced recovery then there is from primary production.

One type of enhanced recovery uses carbon dioxide in what is known as a CO2 flood. The CO2 gas is injected into oil reservoirs, giving them extended life by increasing the amount of oil production. The gas acts as both a piston to move fluid, and as a cleansing agent to collect oil from rock pores. Much of the CO2 can be recycled, and, ultimately, a portion could be sequestered in an abandoned oil reservoir.

The American Association of Petroleum Geologists estimated that the cumulative world production of oil exceeded 750 billion barrels by 1993. Production since that time has raised the cumulative figure to approximately 1,100 billion or 1.1 trillion barrels. This represents a volume of over 42 cubic mi. of oil, equal to covering the state of Illinois in 4 ft. (2.2 m.) of oil. Proven reserves, that is, oil remaining to be pumped out of the ground, are estimated at approximately 1.1 trillion barrels. Assuming that exploration and continued technological advances result in a further 1.1 trillion barrels of oil, ultimately 126 cubic mi. of oil will have been produced. Gasoline accounts for almost half of a barrel, and with other fuels included, such as diesel, the percentage is over 75 percent. The majority of oil produced is combusted and releases greenhouse gases.

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