52 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
Defining a set of objectives is not always an easy task. Specific
circumstances can radically change the methodology required.
The process of making these decisions requires a thorough understanding of the theoretical and practical aspects of reserves and
deliverability.
2.5 Estimation of Reserves in Place
Oil is used by more than 200 nations of the world, but only approximately 40 countries, most of which are oil exporters, produce significant amounts. The precise numbers are likely to change because
of the depletion of the once-vast resources of North America and
South America deriving from the increasing domestic use of oil
by many of the exporters. The number of oil exporters outside the
Middle East and the former Soviet Union will decrease in the coming decades, which in turn will greatly reduce the supply diversity
to the oil-importing nations (Hallock et al., 2004). An increase in
reliance on oil from Persian Gulf countries, West African countries
(especially Nigeria), the former Soviet Union has many strategic,
economic, and political implications.
Universally accepted definitions have not been developed for the
many terms used by geologists, engineers, accountants, and others
to denote various components of crude oil resources because most
of these terms describe estimated and therefore uncertain, rather
than measured, quantities. Particularly common is a general lack
of understanding of the substantial difference between the terms
reserves and resources (Chapter 1) as indicated by the frequent misuse of either term in place of the other.
The amount of oil in a subsurface reservoir is called oil in place
(OIP) and only a fraction of this oil can be recovered from a reservoir and this fraction is called the recovery factor. The portion that
can be recovered is considered to be the reserve, while the portion
of the oil that is non-recoverable (residual oil; Chapter 1) should not
be included unless or until methods are implemented to produce it.
There are a number of different methods of calculating oil
reserves. These methods can be grouped into three general categories: (1) volumetric methods, (2) materials balance method, and
(3) the decline curve method or production performance method.
Volumetric methods attempt to determine the amount of oil
in place by using the size of the reservoir as well as the physical
Defining a set of objectives is not always an easy task. Specific
circumstances can radically change the methodology required.
The process of making these decisions requires a thorough understanding of the theoretical and practical aspects of reserves and
deliverability.
2.5 Estimation of Reserves in Place
Oil is used by more than 200 nations of the world, but only approximately 40 countries, most of which are oil exporters, produce significant amounts. The precise numbers are likely to change because
of the depletion of the once-vast resources of North America and
South America deriving from the increasing domestic use of oil
by many of the exporters. The number of oil exporters outside the
Middle East and the former Soviet Union will decrease in the coming decades, which in turn will greatly reduce the supply diversity
to the oil-importing nations (Hallock et al., 2004). An increase in
reliance on oil from Persian Gulf countries, West African countries
(especially Nigeria), the former Soviet Union has many strategic,
economic, and political implications.
Universally accepted definitions have not been developed for the
many terms used by geologists, engineers, accountants, and others
to denote various components of crude oil resources because most
of these terms describe estimated and therefore uncertain, rather
than measured, quantities. Particularly common is a general lack
of understanding of the substantial difference between the terms
reserves and resources (Chapter 1) as indicated by the frequent misuse of either term in place of the other.
The amount of oil in a subsurface reservoir is called oil in place
(OIP) and only a fraction of this oil can be recovered from a reservoir and this fraction is called the recovery factor. The portion that
can be recovered is considered to be the reserve, while the portion
of the oil that is non-recoverable (residual oil; Chapter 1) should not
be included unless or until methods are implemented to produce it.
There are a number of different methods of calculating oil
reserves. These methods can be grouped into three general categories: (1) volumetric methods, (2) materials balance method, and
(3) the decline curve method or production performance method.
Volumetric methods attempt to determine the amount of oil
in place by using the size of the reservoir as well as the physical