Hubbert made several contributions to geophysics, including a mathematical demonstration that rock in the earth's crust, because it is under immense pressure in large areas, should exhibit plasticity, similar to clay. This demonstration explained the observed results that the earth's crust deforms over time. He also studied the flow of underground fluids. Based on theoretical arguments, Hubbert proposed a constitutive equation for absolute permeability of an underground water or oil reservoir where is the average grain diameter and is a dimensionless proportionality constant. However, Kozeny proposed a constitutive equation for absolute permeability which contains Hubbert's proposal as a factor. Hubbert also presented a force potential, denoted or, that bears his name: Some years later Hubbert showed that Darcy's law can be derived from the Navier-Stokes equation of motion of a viscous fluid. Hubbert is best known for his studies on the size of oil fields and natural gas reserves, and the limits these impose on rates of oil and gas production. He predicted that, for an oil-producing area, from an oil-producing province, a nation, or the planet as a whole, the rate of petroleum production of the reserve over time would resemble a bell curve. Based on his theory, he presented a paper to the 1956 meeting of the American Petroleum Institute in San Antonio, Texas, which predicted that overall petroleum production would peak in the United States between 1965, which he considered most likely, and 1970, which he considered an upper-bound. At first his prediction received much criticism, for the most part because many other predictions of oil capacity had been made over the preceding half century, but these had usually been based on the reserves-to-production ratio, had not taken into account future discoveries, and had proven false. Hubbert became famous when U.S. oil production peaked in 1970 and began to decline, as he had predicted. In 1974, Hubbert projected that global oil production would peak in 1995 "if current trends continue". Various subsequent predictions have been made by others as trends have fluctuated in the intervening years. Hubbert believed that solar power would be a practical renewable energy replacement for fossil fuels, and that nuclear energy in breeder reactors would be able to sustain us for centuries. He also states that "provided world population can somehow be brought under control, we may at last have found an energy supply adequate for our needs for at least the next few centuries of the 'foreseeable future'."
Contributions
Hubbert's contributions to science have been summarized as follows:
Mathematical demonstration that rock in the earth's crust is plastic, and that the earth's crust deforms over time.
Prediction of migration paths of hydrocarbons.
Predictions of peak rates of oil and gas production, based on a consistent mathematical model which ties reserves, discovery rates, and production rates. His model remains highly influential, and has been widely applied to other finite resources.
Renewable resources
Fisheries: At least one researcher has attempted to perform Hubbert linearization on the whaling industry, as well as charting the transparently dependent price of caviar on sturgeon depletion. The Atlantic northwest cod fishery was a renewable resource, but the numbers of fish taken exceeded the fish's rate of recovery. The end of the cod fishery matches the exponential drop of the Hubbert bell curve. Another example is the North Sea cod fishery. The comparison of the cases of fisheries and of mineral extraction tells us that the human pressure on the environment is causing a wide range of resources to go through a depletion cycle which mirrors the Hubbert curve.
