47
3
Origin and Occurrence
3.1 INTRODUCTION
Petroleum is by far the most commonly used source of energy, especially as the source of liquid
fuels and use of petroleum is projected to continue at least in current amounts for several decades
into the current century (Speight, 2011). However, there is petroleum and there is petroleum
and all is not equal! In recent years, the average quality of crude oil has become worse. This is
reflected in a progressive decrease in API gravity (i.e., increase in density) and a rise in sulfur
content. However, it is now believed that there has been a recent tendency for the quality of crude
oil feedstocks to stabilize. Be that as it may, the nature of crude oil refining has been changed
considerably.
The declining reserves of light crude oil have resulted in an increasing need to develop options
to upgrade the abundant supply of known heavy oil reserves. In addition, there is considerable focus
and renewed efforts on adapting recovery techniques to the production of heavy oil and tar sand
bitumen (Chapter 7) (Speight, 2009).
Fossil fuels are those fuels, namely, coal, petroleum (including heavy oil and bitumen), natural
gas, and oil shale, produced by the decay of plant remains over geological time (Speight, 1990).
They are carbon-based and represent a vast source of energy. Resources such as heavy oil and bitumen in tar sand formations are also discussed in this text. These represent an unrealized potential,
with liquid fuels from petroleum being only a fraction of those that could ultimately be produced
from heavy oil and tar sand bitumen.
In fact, at the present time, the majority of the energy consumed by humans is produced from
fossil fuels (petroleum, ca. 38%–40%; coal, ca. 31%–35%; natural gas, ca. 20%–25%) with the
remainder of the energy requirements coming from nuclear and hydroelectric sources.
Petroleum is scattered throughout the Earth’s crust, which is divided into natural groups or
strata, categorized in the order of their antiquity (Table 3.1). These divisions are recognized by the
distinctive systems of organic debris (as well as fossils, minerals, and other characteristics) that
form a chronological time chart that indicates the relative ages of the Earth’s strata. It is generally
acknowledged that carbonaceous materials such as petroleum occur in all these geological strata
from the Precambrian to the recent epoch, and the origin of petroleum within these formations is a
question that remains open to conjecture and the basis for much research.
Indeed, petroleum technology, in one form or another, is with us until suitable alternative forms
of energy are readily available. Therefore, a thorough understanding of the benefits and limitations
of petroleum recovery and processing is necessary and will be introduced in this book.
3.2 ORIGIN
There are two theories on the origin of carbon fuels: the abiogenic theory and the biogenic
theory (Kenney et al., 2001, 2002). The two theories have been intensely debated since the
1860s, shortly after the discovery of widespread occurrence of petroleum. It is not the intent of
this section to sway the reader in his or her views of the origin of petroleum and natural gas.
The intent is to place before the reader both points of view from which the reader can further
research and decide.
3
Origin and Occurrence
3.1 INTRODUCTION
Petroleum is by far the most commonly used source of energy, especially as the source of liquid
fuels and use of petroleum is projected to continue at least in current amounts for several decades
into the current century (Speight, 2011). However, there is petroleum and there is petroleum
and all is not equal! In recent years, the average quality of crude oil has become worse. This is
reflected in a progressive decrease in API gravity (i.e., increase in density) and a rise in sulfur
content. However, it is now believed that there has been a recent tendency for the quality of crude
oil feedstocks to stabilize. Be that as it may, the nature of crude oil refining has been changed
considerably.
The declining reserves of light crude oil have resulted in an increasing need to develop options
to upgrade the abundant supply of known heavy oil reserves. In addition, there is considerable focus
and renewed efforts on adapting recovery techniques to the production of heavy oil and tar sand
bitumen (Chapter 7) (Speight, 2009).
Fossil fuels are those fuels, namely, coal, petroleum (including heavy oil and bitumen), natural
gas, and oil shale, produced by the decay of plant remains over geological time (Speight, 1990).
They are carbon-based and represent a vast source of energy. Resources such as heavy oil and bitumen in tar sand formations are also discussed in this text. These represent an unrealized potential,
with liquid fuels from petroleum being only a fraction of those that could ultimately be produced
from heavy oil and tar sand bitumen.
In fact, at the present time, the majority of the energy consumed by humans is produced from
fossil fuels (petroleum, ca. 38%–40%; coal, ca. 31%–35%; natural gas, ca. 20%–25%) with the
remainder of the energy requirements coming from nuclear and hydroelectric sources.
Petroleum is scattered throughout the Earth’s crust, which is divided into natural groups or
strata, categorized in the order of their antiquity (Table 3.1). These divisions are recognized by the
distinctive systems of organic debris (as well as fossils, minerals, and other characteristics) that
form a chronological time chart that indicates the relative ages of the Earth’s strata. It is generally
acknowledged that carbonaceous materials such as petroleum occur in all these geological strata
from the Precambrian to the recent epoch, and the origin of petroleum within these formations is a
question that remains open to conjecture and the basis for much research.
Indeed, petroleum technology, in one form or another, is with us until suitable alternative forms
of energy are readily available. Therefore, a thorough understanding of the benefits and limitations
of petroleum recovery and processing is necessary and will be introduced in this book.
3.2 ORIGIN
There are two theories on the origin of carbon fuels: the abiogenic theory and the biogenic
theory (Kenney et al., 2001, 2002). The two theories have been intensely debated since the
1860s, shortly after the discovery of widespread occurrence of petroleum. It is not the intent of
this section to sway the reader in his or her views of the origin of petroleum and natural gas.
The intent is to place before the reader both points of view from which the reader can further
research and decide.