Page 15 - Primer on Enhanced Oil Recovery

6 Primer on Enhanced Oil Recovery

Table 2.1 Elemental composition of crude oil and natural gas.
Element Crude oil (at%) Natural gas (at%)

Carbon 82 88 66 79
Hydrogen 11 15 1 25
Sulfur 0.05 2 0 0.18
Nitrogen 0.06 2 1 16
Oxygen 0.2 2 0

C n H 2n12 , known also as paraffines), alkenes (linear molecules, double bonds, C n H 2 ,
commonly known as olefins) and arenes (molecules with aromatic ring(s), com-
monly known as naphthenes or cycloparafines). Properties of oil (viscosity, for
instance) depend on the chemical composition, temperature and pressure on the first
place.
The color of crude oils varies in broad spectra from yellow to dark brown,
almost black, but there is also oil that has a yellow-green, brown-red color. In some
formations oil is even colorless. The color and smell of oil is mostly defined by
presence in the oil natural mixture of nitrogen-, sulfur- and oxygen-containing com-
pounds. Some ideas about oil and gas elemental composition can be formed on the
basis if Table 2.1.
Many properties of oil related to its density (weight per volume). Not all oil
properties can be easily bunched together under this banner, nevertheless, most
commonly, oil density can be used as a first step guidance, it represents
marketable properties and, in some aspects, oil monetary value. Historically and
practicable the oil density is expressed in relation to the density of fresh water at
the standard temperature (see later).
Most commonly used scale expresses oil density in so named API (American
Petroleum Institute) scale,

0

API gravity 5 ð141:5=ρÞ 2 131:5; (2.1)
where ρ is specific gravity, also known as density. All measurements should be
done at the standard temperature 2 60 F (15.6 C). These measuring conditions

0
are known as “standard conditions”. Gravity of fresh water on this scale is 10 API
(Fig. 2.1).
It is possible easily to use oil gravity to account for barrels of crude (volumetri-
cally 1 barrel of oil crude contains 159 L of oil) in metric tonne.
N b=t 5 API 1 131:5ð Þ=141:5 0:159 (2.2)

Oil volume as a rule are measured in barrels. One barrel volume is equal to 42
USA gallons volume at the standard conditions.