Petroleum and natural gas have similar origin and often
occur together in geologic formations, and their global distribution and
production is discussed together in the entry by McCabe. This entry makes clear
the distinction between reserves and resources. Reserves represent only that
fraction of the resource base that can be economically recovered using current
technology. These are not fixed quantities as both technology and economics
change over time. Global annual production (and consumption) of oil in 2010 was
31 billion barrels and of natural gas was around 120 trillion cubic feet. In
energy units, they correspond to 180 EJ of oil and 120 EJ of natural gas. The
current reserves are estimated at 1,236 billion barrels of conventional oil
(7,500 EJ) and 6,545 tcf of natural gas (6,500 EJ). The current reserves to
production ratio (R/P) is about 40 for oil and about 55 for natural gas. The
R/P ratio has often been mistakenly taken as the time to exhaustion, but new
discoveries as well as advances in technology add to the reserves. In the case
of oil, for example, the R/P ratio has stayed around 40–50 years for more than
60 years even with the steadily increasing oil consumption. In addition, there
are also unconventional accumulations of these hydrocarbon resources and
extracting them requires development of new technologies. In the case of oil,
the unconventional resources are oil sands, oil shale, and heavy oil.
Unconventional resources of natural gas are coal bed methane, tight gas, shale
gas, and gas hydrates. These unconventional resources are vast and have the
potential of more than doubling our resource endowment.
Exploration and production of oil from sedimentary deposits
and oil sands is the subject of an entry by Speight. The processes for
recovering oil could be a simple matter of drilling into the formation with the
oil flowing to the surface under its own pressure, or it may require injection
of gases, fluids, and surfactants to coax it to flow. In extreme cases, it may
even require underground combustion of a portion of the resource to release the
oil. Speight describes the chemical and physical factors that govern the flow
of oil and the technology options currently available. In a different entry,
Speight provides and account of the different processes such as distillation,
catalytic cracking, hydrotreating, reforming, and DE asphalting used in the
refining of crude oil. This entry also deals with environmental effects of the
gaseous, liquid, and solid effluents from these processes. Production of oil
from shale is principally achieved by retorting of shale, or other thermal
processes including in situ pyrolysis. Oja and Suuberg detail the chemistry and
technology of these processes in the entry.
Petroleum is a
mixture which is mainly composed of hydrocarbon compounds and exists naturally
in gas, liquid, and solid in nature. It includes crude oil and natural gas.
This is a broad definition of petroleum. Narrowly, petroleum is a flammable
liquid or solid mineral mainly composed of a variety of hydrocarbons. Crude oil
is the unprocessed liquid petroleum which is recovered from oil wells.
Petroleum is a thick, flammable, yellow-to-black mixture of
gaseous, liquid, and solid hydrocarbons that occurs naturally beneath the Earth’s surface, can be separated into fractions including natural
gas, gasoline, naphtha, kerosene, fuel and lubricating oils, paraffin wax, and
asphalt and is used as raw material for a wide variety of derivative products.
Petroleum is a dark-colored thick flammable crude oil
occurring in sedimentary rocks around the Persian Gulf, in parts of North and
South America, and below the North Sea, consisting mainly of hydrocarbons.
Fractional distillation separates the crude oil into petrol, paraffin, diesel
oil, lubricating oil, etc. Fuel oil, paraffin wax, asphalt, and carbon black
are extracted from the residue.
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