Energy, whether it was sunlight or heat from a wood fire, has always been important to society. However, with the onset of the industrial revolution over 200 years ago, wood alone could no longer support the increasing energy demand. The world quickly turned to coal to satisfy its energy needs, and it has been reliant on fossil fuels ever since. Despite the inroads renewable and nuclear energies have made in recent decades, the vast majority of energy used by society still comes from the three main fossil fuels: petroleum, natural gas, and coal. As a result, it is important to know how these fuels were formed, the rates at which they are produced and consumed, and how much is economically recoverable for future use.
The formation of petroleum and natural gas began hundreds of millions of years ago as energy from the sun in the form of light radiated toward the earth. Algae that were in the ocean during this time used the sun¡¯s radiant energy to produce energy of their own through the process of photosynthesis. Plankton, being unable to produce energy on its own, consumed algae to obtain energy. When the algae and plankton died, they fell to the ocean floor and accumulated in the mud. As accumulation continued, pressure and temperature were increased on the underlying layers of organic mud. When the pressure became great enough, the mud lithified into organic-rich shale that is referred to as the source rock. If this source rock is exposed to temperatures between 80¢ªC and 160¢ªC, the organic matter forms into oil. Natural gas will form if the source rock is exposed to temperatures between 80¢ªC and 225¢ªC(Marshak 431-2). The ¡°gas window¡± overlaps the ¡°oil window¡±, which means the formation of oil and natural gas can occur at the same temperatures. This explains why natural gas is often found in oil wells. However, when temperatures exceed 160¢ªC, all of the oil in the sources rock burns off to form natural gas. So source rock that is exposed to these high temperatures accounts for the formation of natural gas wells in which there is no oil.
The source rock is often times buried beneath a layer of porous sedimentary rock. The pores in this rock are filled with water, so it is called the reservoir rock. Since oil and gas float on water, the hydrocarbons in the source rock rise through the reservoir rock. They continued to rise until they encountered an impermeable layer of rock, where they stop and form a reserve. The natural gas, since it is lighter, will always rest on top of any oil in the reserve(Marshak 433-4).
Oil has become the most widely used energy source in the world. This is because oil is both easy to transport and flexible in its uses, unlike natural gas, which is costly to transport, and coal, which currently has limited applications. The result is that thirty-eight percent of energy used in the United States comes from the burning of oil(Ristinen 17). Transportation, which gets almost...