Page 22 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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2 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS
gas), liquids (crude oil), semisolids (bitumen), or solids (wax
space to store the hydrocarbons produced. The conditions re-
or asphaltite). Liquid fuels are normally produced from liq- organic compounds into petroleum, and (3) a sealed reservoir
uid hydrocarbons, although conversion of nonliquid hydro- quired for the process of conversion of organic compounds
carbons such as coal, oil shale, and natural gas to liquid fuels into petroleum as shown through Eq. (1.2) are (1) geologic
is being investigated. In this book, only petroleum hydrocar- time of about 1 million years, (2) maximum pressure of
bons in the form of gas or liquid, simply called petroleum flu- about 17 MPa (2500 psi), and (3) temperature not exceed-
ids, are considered. Liquid petroleum is also simply called oil. ing 100–120 C(∼210–250 F). If a leak occurred sometime
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Hydrocarbon gases in a reservoir are called a natural gas or in the past, the exploration well will encounter only small
simply a gas. An underground reservoir that contains hydro- amounts of residual hydrocarbons. In some cases bacteria
carbons is called petroleum reservoir and its hydrocarbon con- may have biodegraded the oil, destroying light hydrocarbons.
tents that can be recovered through a producing well is called An example of such a case would be the large heavy oil accu-
reservoir fluid. Reservoir fluids in the reservoirs are usually in mulations in Venezuela. The hydrocarbons generated grad-
contact with water in porous media conditions and because ually migrate from the original beds to more porous rocks,
they are lighter than water, they stay above the water level such as sandstone, and form a petroleum reservoir. A series
under natural conditions. of reservoirs within a common rock is called an oil field.
Although petroleum has been known for many centuries, Petroleum is a mixture of hundreds of different identifiable
the first oil-producing well was discovered in 1859 by E.L. hydrocarbons, which are discussed in the next section. Once
Drake in the state of Pennsylvania and that marked the petroleum is accumulated in a reservoir or in various sedi-
birth of modern petroleum technology and refining. The ments, hydrocarbon compounds may be converted from one
main elements of petroleum are carbon (C) and hydrogen form to another with time and varying geological conditions.
(H) and some small quantities of sulfur (S), nitrogen (N), This process is called in-situ alteration, and examples of chem-
and oxygen (O). There are several theories on the formation ical alteration are thermal maturation and microbial degra-
of petroleum. It is generally believed that petroleum is de- dation of the reservoir oil. Examples of physical alteration of
rived from aquatic plants and animals through conversion of petroleum are the preferential loss of low-boiling constituents
organic compounds into hydrocarbons. These animals and by the diffusion or addition of new materials to the oil in
plants under aquatic conditions have converted inorganic place from a source outside the reservoir [1]. The main dif-
compounds dissolved in water (such as carbon dioxide) to ference between various oils from different fields around the
organic compounds through the energy provided by the sun. world is the difference in their composition of hydrocarbon
An example of such reactions is shown below: compounds. Two oils with exactly the same composition have
identical physical properties under the same conditions [2].
(1.1) 6CO 2 + 6H 2 O + energy → 6O 2 + C 6 H 12 O 6
A good review of statistical data on the amount of oil and
in which C 6 H 12 O 6 is an organic compound called carbohy- gas reservoirs, their production, processing, and consump-
drate. In some cases organic compounds exist in an aquatic tion is usually reported yearly by the Oil and Gas Journal
environment. For example, the Nile river in Egypt and the (OGJ). An annual refinery survey by OGJ is usually published
Uruguay river contain considerable amounts of organic ma- in December of each year. OGJ also publishes a forecast and
terials. This might be the reason that most oil reservoirs are review report in January and a midyear forecast report in
located near the sea. The organic compounds formed may be July of each year. In 2000 it was reported that total proven oil
decomposed into hydrocarbons under certain conditions. reserves is estimated at 1016 billion bbl (1.016 × 10 12 bbl),
(1.2) (CH 2 O) n → xCO 2 + yCH z which for a typical oil is equivalent to approximately 1.39 ×
11
10 tons. The rate of oil production was about 64.6 million
in which n, x, y, and z are integer numbers and yCH z is the bbl/d (∼3.23 billion ton/year) through more than 900 000 pro-
closed formula for the produced hydrocarbon compound. ducing wells and some 750 refineries [3, 4]. These numbers
Another theory suggests that the inorganic compound cal- vary from one source to another. For example, Energy Infor-
cium carbonate (CaCO 3 ) with alkali metal can be converted to mation Administration of US Department of Energy reports
calcium carbide (CaC 2 ), and then calcium carbide with water world oil reserves as of January 1, 2003 as 1213.112 billion
(H 2 O) can be converted to acetylene (C 2 H 2 ). Finally, acetylene bbl according to OGJ and 1034.673 billion bbl according to
can be converted to petroleum [1]. Conversion of organic mat- World Oil (www.eia.doe.gov/emeu/iea). According to the OGJ
ters into petroleum is called maturation. The most important worldwide production reports (Oil and Gas Journal, Dec. 22,
factors in the conversion of organic compounds to petroleum 2003, p. 44), world oil reserves estimates changed from 999.78
hydrocarbons are (1) heat and pressure, (2) radioactive rays, in 1995 to 1265.811 billion bbl on January 1, 2004. For the
such as gamma rays, and (3) catalytic reactions. Vanadium- same period world gas reserves estimates changed from 4.98×
and nickel-type catalysts are the most effective catalysts in 10 15 scf to 6.0683 × 10 15 scf. In 2003 oil consumption was
the formation of petroleum. For this reason some of these about 75 billion bbl/day, and it is expected that it will in-
metals may be found in small quantities in petroleum fluids. crease to more than 110 million bbl/day by the year 2020.
The role of radioactive materials in the formation of hydro- This means that with existing production rates and reserves,
carbons can be best observed through radioactive bombard- it will take nearly 40 years for the world’s oil to end. Oil
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ing of fatty acids (RCOOH) that form paraffin hydrocarbons. reserves life (reserves-to-production ratio) in some selected
Occasionally traces of radioactive materials such as uranium countries is given by OGJ (Dec. 22, 2003, p. 45). According
and potassium can also be found in petroleum. In summary, to 2003 production rates, reserves life is 6.1 years in UK,
the following steps are required for the formation of hydrocar- 10.9 years in US, 20 years in Russia, 5.5 years in Canada,
bons: (1) a source of organic material, (2) a process to convert 84 years in Saudi Arabia, 143 years in Kuwait, and 247 years

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