Oil depletion occurs in the second half of the production curve of an oil well, oil field, or the average of total world oil production. 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, when the peak of production is passed, production rates enter an exponential decline.[3]
The American Petroleum Institute estimated in 1999 the world's oil supply would be depleted between 2062 and 2094, assuming total world oil reserves at between 1.4 and 2 trillion barrels and consumption at 80 million barrels per day.[4] In 2004, total world reserves were estimated to be 1.25 trillion barrels and daily consumption was about 85 million barrels, shifting the estimated oil depletion year to 2057.[1] The United States Energy Information Administration predicts world consumption of oil will increase to 98.3 million barrels per day in 2015 and 118 million barrels per day in 2030.
Resource availability
The world's oil supply is fixed because it is no longer being naturally formed. Several hundred million years ago, plankton and bacteria (that fed on decaying plankton) thrived in the oceans of the then carbon dioxide rich atmosphere. At that time, volcanic sulphur dioxide lined the ocean floor, preventing living creatures from inhabiting, and therefore consuming, the plankton and bacteria after their death. Those plankton and bacteria that settled in porous sandstone or limestone, and those plankton and bacteria that were then capped by shale or salt, were allowed to heat and become pressurized to form oil.
Production decline models
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, a set of fields, or the world.
Oil well production decline
Theoretical oil well production curve.
Oil well production curves typically end in an exponential decline.[3] At natural rates, oil well production curves appear similar to a bell curve, a phenomenon known as the Hubbert curve. The typical decline is a rapid drop in production, and eventually a leveling off to a point at which they no longer produce profitable amounts.[3] Such wells are referred to as marginal or stripper wells.
The shape of production curve of an oil well can be affected by a number of factors:
* Well may be restricted by choice by lack of market demand or government regulation. This flattens the peak of the curve, but will not change the well's total production significantly.
* Hydraulic fracturing (fracing) or acidizing may be used to cause a sharp spike in production, and may increase the recoverable reserves of a given well.
* The field may undergo a secondary or tertiary recovery project, discussed in the next section.