68
The Chemistry and Technology of Petroleum
The term inferred reserves is also commonly used in addition to, or in place of, potential reserves.
Inferred reserves are regarded as of a higher degree of accuracy than potential reserves, and the
term is applied to those reserves that are estimated using an improved understanding of reservoir
frameworks. The term also usually includes those reserves that can be recovered by further development of recovery technologies.
The differences between the data obtained from these various estimates can be considerable, but
it must be remembered that any data about the reserves of petroleum (and, for that matter, about any
other fuel or mineral resource) will always be open to questions about the degree of certainty. Thus,
in reality, and in spite of the use of self-righteous word-smithing, proven reserves may be a very
small part of the total hypothetical and/or speculative amounts of a resource.
At some time in the future, certain resources may become reserves. Such a reclassification can
arise as a result of improvements in recovery techniques that may either make the resource accessible or bring about a lowering of the recovery costs and render winning of the resource an economical proposition. In addition, other uses may also be found for a commodity, and the increased
demand may result in an increase in price. Alternatively, a large deposit may become exhausted and
unable to produce any more of the resource, thus forcing production to focus on a resource that is
lower grade but has a higher recovery cost.
It is very rare that petroleum (the exception being tar sand deposits, from which most of the volatile material has disappeared over time) does not occur without an accompanying cover of gas. It is
therefore important, when describing reserves of petroleum, to also acknowledge the occurrence,
properties, and character of the gaseous material, more commonly known as natural gas.
The Society for Petroleum Engineers has developed a resource classification system
(Figure 3.3) that moves away from systems in which all quantities of petroleum that are estimated
to be initially-in-place are used. Some users consider only the estimated recoverable portion to
Low
estimate
Best
estimate
Unrecoverable
Range of uncertainty
High
estimate
Undiscovered
petroleum-initially-in-place
Proved
plus
probable
Proved
plus
probable
plus
possible
Production
Proved
Sub-commercial
Commercial
Best
estimate
High
estimate
Low
estimate
Total petroleum-initially-in-place
Discovered petroleum-initially-in-place
Prospective
resources
Unrecoverable
Contingent
resources
Reserves
Not to scale
FIGURE 3.3 Resources classification system.
The Chemistry and Technology of Petroleum
The term inferred reserves is also commonly used in addition to, or in place of, potential reserves.
Inferred reserves are regarded as of a higher degree of accuracy than potential reserves, and the
term is applied to those reserves that are estimated using an improved understanding of reservoir
frameworks. The term also usually includes those reserves that can be recovered by further development of recovery technologies.
The differences between the data obtained from these various estimates can be considerable, but
it must be remembered that any data about the reserves of petroleum (and, for that matter, about any
other fuel or mineral resource) will always be open to questions about the degree of certainty. Thus,
in reality, and in spite of the use of self-righteous word-smithing, proven reserves may be a very
small part of the total hypothetical and/or speculative amounts of a resource.
At some time in the future, certain resources may become reserves. Such a reclassification can
arise as a result of improvements in recovery techniques that may either make the resource accessible or bring about a lowering of the recovery costs and render winning of the resource an economical proposition. In addition, other uses may also be found for a commodity, and the increased
demand may result in an increase in price. Alternatively, a large deposit may become exhausted and
unable to produce any more of the resource, thus forcing production to focus on a resource that is
lower grade but has a higher recovery cost.
It is very rare that petroleum (the exception being tar sand deposits, from which most of the volatile material has disappeared over time) does not occur without an accompanying cover of gas. It is
therefore important, when describing reserves of petroleum, to also acknowledge the occurrence,
properties, and character of the gaseous material, more commonly known as natural gas.
The Society for Petroleum Engineers has developed a resource classification system
(Figure 3.3) that moves away from systems in which all quantities of petroleum that are estimated
to be initially-in-place are used. Some users consider only the estimated recoverable portion to
Low
estimate
Best
estimate
Unrecoverable
Range of uncertainty
High
estimate
Undiscovered
petroleum-initially-in-place
Proved
plus
probable
Proved
plus
probable
plus
possible
Production
Proved
Sub-commercial
Commercial
Best
estimate
High
estimate
Low
estimate
Total petroleum-initially-in-place
Discovered petroleum-initially-in-place
Prospective
resources
Unrecoverable
Contingent
resources
Reserves
Not to scale
FIGURE 3.3 Resources classification system.