HISTORY AND TERMINOLOGY OF CRUDE OIL 25
There are several general definitions that have been applied
to natural gas. For example, associated or dissolved natural gas
occurs either as free gas or as gas in solution in the petroleum. Gas
that occurs as a solution in the petroleum is dissolved gas, whereas
the gas that exists in contact with the petroleum (gas cap) is associated gas. In addition, lean gas is gas in which methane is the major
constituent and wet gas contains considerable amounts of the
higher molecular weight hydrocarbons. Sour gas contains hydrogen sulfide, whereas sweet gas contains very little, if any, hydrogen sulfide. In direct contrast to the terminology of the petroleum
industry where the residue (residuum, resid) is the high boiling
material left after distillation, residue gas is natural gas from which
the higher molecular weight (higher boiling) hydrocarbons have
been extracted and so is the lowest boiling hydrocarbon in natural
gas. Finally casing head gas (casinghead gas) is derived from petroleum, but is separated at the well-head separation facility.
To further define the terms dry and wet in quantitative measures,
the term dry natural gas indicates that there is less than 0.1 gallon
(1 gallon, US, = 264.2 m
3
) of gasoline vapor (higher molecular
weight paraffins) per 1000 ft
3
(1 ft
3
= 0.028 m
3
). The term wet natural gas indicates that there are such paraffins present in the gas — in
fact, more than 0.1 gal/1000 ft
3
.
Other components such as carbon dioxide (C0 2 ), hydrogen sulfide (H 2 S), mercaptans (thiols; R-SH), as well as trace amounts of
other constituents may also be present. Thus, there is no single
organization of components that maybe termed typical natural gas.
1.4.3 Heavy Oil
Heavy oil is a type of petroleum that is different from conventional
petroleum insofar as it is much more difficult to recover from the
subsurface reservoir and has a much higher viscosity (and lower
API gravity) than conventional petroleum, and primary recovery
of heavy oil usually requires thermal stimulation of the reservoir.
Petroleum and heavy oil have been very generally defined in terms
of physical properties (Section 1.2). For example, heavy oil was considered to be crude oil that had gravity somewhat less than 20°API
with tar sand bitumen falling into the API gravity range <10°. For
example, Cold Lake heavy crude oil has an API gravity equal to 12°
and tar sand bitumen, usually has an API gravity in the range of 5-10°
(Athabasca bitumen = 8°API). However, classification of crude oil by
There are several general definitions that have been applied
to natural gas. For example, associated or dissolved natural gas
occurs either as free gas or as gas in solution in the petroleum. Gas
that occurs as a solution in the petroleum is dissolved gas, whereas
the gas that exists in contact with the petroleum (gas cap) is associated gas. In addition, lean gas is gas in which methane is the major
constituent and wet gas contains considerable amounts of the
higher molecular weight hydrocarbons. Sour gas contains hydrogen sulfide, whereas sweet gas contains very little, if any, hydrogen sulfide. In direct contrast to the terminology of the petroleum
industry where the residue (residuum, resid) is the high boiling
material left after distillation, residue gas is natural gas from which
the higher molecular weight (higher boiling) hydrocarbons have
been extracted and so is the lowest boiling hydrocarbon in natural
gas. Finally casing head gas (casinghead gas) is derived from petroleum, but is separated at the well-head separation facility.
To further define the terms dry and wet in quantitative measures,
the term dry natural gas indicates that there is less than 0.1 gallon
(1 gallon, US, = 264.2 m
3
) of gasoline vapor (higher molecular
weight paraffins) per 1000 ft
3
(1 ft
3
= 0.028 m
3
). The term wet natural gas indicates that there are such paraffins present in the gas — in
fact, more than 0.1 gal/1000 ft
3
.
Other components such as carbon dioxide (C0 2 ), hydrogen sulfide (H 2 S), mercaptans (thiols; R-SH), as well as trace amounts of
other constituents may also be present. Thus, there is no single
organization of components that maybe termed typical natural gas.
1.4.3 Heavy Oil
Heavy oil is a type of petroleum that is different from conventional
petroleum insofar as it is much more difficult to recover from the
subsurface reservoir and has a much higher viscosity (and lower
API gravity) than conventional petroleum, and primary recovery
of heavy oil usually requires thermal stimulation of the reservoir.
Petroleum and heavy oil have been very generally defined in terms
of physical properties (Section 1.2). For example, heavy oil was considered to be crude oil that had gravity somewhat less than 20°API
with tar sand bitumen falling into the API gravity range <10°. For
example, Cold Lake heavy crude oil has an API gravity equal to 12°
and tar sand bitumen, usually has an API gravity in the range of 5-10°
(Athabasca bitumen = 8°API). However, classification of crude oil by