Tidal Current Energy

The Future of Oil and Gas Fossil Fuels
conventional oil, of which about 96 � 10 9 m 3 lie in the Middle East and 85 % in
9 the Eastern hemisphere [35] . Based on these reserve estimates we can naively
speculate about when the hydrocarbon-based economy will cease. To do so, it
is assumed both the consumption rate [52] is constant at about 16 � 10 6 m 3� d � 1 ,
which is equivalent to a constant global population, and if no more reserves
are discovered there is a further 26 a remaining. However, for natural gas the
recoverable accumulations amount to about 4 � 10 14 m 3 and the world consumption
is about 3 � 10 12 m 3 �a � 1 ; thus, with the same assumption this leads to a further
100 a of natural gas use [51] .
There are three methods of recovery: primary, secondary and tertiary. For
conventional wells, primary production uses natural reservoir pressure to force
the oil to the surface and has a recovery factor of 0.2. When the pressure has
depleted to prevent adequate production from the natural pressure, then beam
or electrical submersible pumps can be used, or a fluid, such as water, natural
gas, air or carbon dioxide, can be injected to maintain the pressure. This
accounts for an increase in recovery factor by 0.15 to about 0.35. In some cases,
the remaining oil has a viscosity similar to heavy oil and bitumen, and requires
tertiary recovery to reduce viscosity by either thermal or non-thermal methods.
Steam injection is the most common form of thermal recovery. Injected
carbon dioxide acts as a diluent and forms the majority of non-thermal tertiary
recovery, although for some hydrocarbons this can give rise to precipitation
of asphaltenes [57] . Tertiary recovery permits an increase in recovery factor by
between 0.05 and 0.1 to yield, typically, an overall recovery factor that ranges
from 0.4 to 0.5. Clearly, there is room for improvement for oil, while natural gas
reservoirs can have recovery factors of 0.75.
3.1.1 . Energy supply and demand
A logistic function or logistic curve has been used to describe the S-shaped
curve observed for growth, where in the initial stage it is exponential then, as
saturation begins, the growth slows and at maturity stops. A sigmoid is a special
case of a logistic function. Cumulative production as a function of time from
an oil reservoir can be described by a logistic function. In 1949, Hubbert used
the derivative of a logistic function with respect to time to describe the production
of Pennsylvanian anthracite that peaked during the 1920s [58] . The analyses
included production rates, population growth, and the discovery and replenishment
of depleted reservoirs. Hubbert used these analyses for oil production and
developed the so-called Hubbert curve (derivative of the logistic function) that
predicted the peak US production of oil that occurred during the 1970s [58] . 10
Similar analyses that include estimates of the world population [59] and oil
reserves have been used by others to estimate when oil production will peak
[55,60,61] ; some suggest that this will be soon relative to the time of writing
9 http://pubs.usgs.gov/fs/fs070-03/fs070-03.html .
10 The Hubbert and logistic curves are for an experimentalist analogous in form to the real and
imaginary components of a resonance frequency.
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