Oil depletion
Oil depletion is the decline in oil production of a well, oil field, or geographic area. The Hubbert peak theory makes predictions of production rates based on prior discovery rates and anticipated production rates. Hubbert curves predict that the production curves of non-renewing resources approximate a bell curve. Thus, according to this theory, when the peak of production is passed, production rates enter an irreversible decline.
The United States Energy Information Administration predicted in 2006 that world consumption of oil will increase to 98.3 million barrels per day (15,630,000 m3/d) (mbd) in 2015 and 118 million barrels per day in 2030. With 2009 world oil consumption at 84.4 mbd, reaching the projected 2015 level of consumption would represent an average annual increase between 2009 and 2015 of 2.7% per year.
The World's natural oil supply is fixed because petroleum is naturally formed far too slowly to be replaced at the rate at which it is being extracted. Over many millions of years, plankton, bacteria, and other plant and animal matter became buried in sediments on the ocean floor. When conditions were right – a lack of oxygen for decomposition, and sufficient depth and temperature of burial – these organic remains were converted into petroleum compounds, while the sediment accompanying them was converted into sandstone, siltstone, and other porous sedimentary rock. When capped by impermeable rocks such as shale, salt, or igneous intrusions, they formed the petroleum reservoirs which are exploited today.
For the short and medium-term, oil production decline occurs in a predictable manner based on geological circumstances, governmental policies, and engineering practices. The shape of the decline curve varies depending upon whether one considers a well, a field, or a set of fields. In the longer term, technological developments have defied some of the predictions.
An individual oil well usually produces at its maximum rate at the start of its life; the production rate eventually declines to a point at which it no longer produces profitable amounts. The shape of the decline curve depends on the oil reservoir and the reservoir drive mechanism. Wells in water-drive and gas-cap drive reservoirs often produce at a near constant rate until the encroaching water or expanding gas cap reaches the well, causing a sudden decline in oil production. Wells in gas solution drive and oil expansion drive reservoirs have exponential or hyperbolic declines: rapid declines at first, then leveling off.
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