70
The Chemistry and Technology of Petroleum
which are those quantities of petroleum that are estimated, on a given date, to be potentially
recoverable from undiscovered accumulations.
Estimated ultimate recovery (EUR) is the quantity of petroleum which is estimated, on a given
date, to be potentially recoverable from an accumulation, plus those quantities already produced
therefrom. Estimated ultimate recovery not a resource category but it is a term that may be applied
to an individual accumulation of any status/maturity (discovered or undiscovered).
Petroleum quantities classified as reserves, contingent resources, or prospective resources
should not be aggregated with each other without due consideration of the significant differences
in the criteria associated with their classification. In particular, there may be a significant risk that
accumulations containing contingent resources or prospective resources will not achieve commercial production.
The range of uncertainty (Figure 3.3) reflects a reasonable range of estimated potentially recoverable volumes for an individual accumulation. Any estimation of resource quantities for an accumulation is subject to both technical and commercial uncertainties, and should, in general, be quoted
as a range. In the case of reserves, and where appropriate, this range of uncertainty can be reflected
in estimates for proved reserves (1P), proved plus probable reserves (2P), and proved plus probable
plus possible reserves (3P) scenarios. For other resource categories, the terms low estimate, best
estimate, and high estimate are recommended.
The term best estimate is used as a generic expression for the estimate considered to be the closest to the quantity that will actually be recovered from the accumulation between the date of the
estimate and the time of abandonment. If probabilistic methods are used, this term would generally
be a measure of central tendency of the uncertainty distribution. The terms low estimate and high
estimate should provide a reasonable assessment of the range of uncertainty in the best estimate.
For undiscovered accumulations (prospective resources) the range will, in general, be substantially greater than the ranges for discovered accumulations. In all cases, however, the actual range
will be dependent on the amount and quality of data (both technical and commercial) available for
that accumulation. As more data become available for a specific accumulation (e.g., additional wells
and reservoir performance data) the range of uncertainty in the estimated ultimate recovery for that
accumulation should be reduced.
The low estimate, best estimate, and high estimate of potentially recoverable volumes should
reflect some comparability with the reserves categories of proved reserves, proved plus probable
reserves, and proved plus probable plus possible reserves, respectively. While there may be a
significant risk that sub-commercial or undiscovered accumulations will not achieve commercial
production, it is useful to consider the range of potentially recoverable volumes independently of
such a risk.
3.3.2 ConventIonAl Petroleum
At the present time, several countries are recognized as producers of petroleum and have available reserves. These available reserves have been defined (Campbell, 1997), but not quite in the
manner outlined earlier. For example, on a worldwide basis the produced conventional crude oil
is estimated to be approximately 784 billion (784 × 10 9 ) bbl with approximately 836 billion bbl
remaining as reserves. It is also estimated that there are 180 billion bbl, which remain to be discovered with approximately 1 trillion (1 × 10 12 ) bbl yet to be produced. The annual depletion rate
is estimated to be 2.6%.
In addition, the crude oils available today to the refinery are quite different in composition and
properties to those available some 50–60 years ago. The current crude oils are somewhat heavier
insofar as they have higher proportions of nonvolatile (asphaltic) constituents. In fact, by the standards of yesteryears, many of the crude oils currently in use would have been classified as heavy
feedstock, bearing in mind that they may not approach the definitions used today for heavy crude
oil (Chapter 1). Changes in feedstock character, such as this tendency to heavier materials, require
The Chemistry and Technology of Petroleum
which are those quantities of petroleum that are estimated, on a given date, to be potentially
recoverable from undiscovered accumulations.
Estimated ultimate recovery (EUR) is the quantity of petroleum which is estimated, on a given
date, to be potentially recoverable from an accumulation, plus those quantities already produced
therefrom. Estimated ultimate recovery not a resource category but it is a term that may be applied
to an individual accumulation of any status/maturity (discovered or undiscovered).
Petroleum quantities classified as reserves, contingent resources, or prospective resources
should not be aggregated with each other without due consideration of the significant differences
in the criteria associated with their classification. In particular, there may be a significant risk that
accumulations containing contingent resources or prospective resources will not achieve commercial production.
The range of uncertainty (Figure 3.3) reflects a reasonable range of estimated potentially recoverable volumes for an individual accumulation. Any estimation of resource quantities for an accumulation is subject to both technical and commercial uncertainties, and should, in general, be quoted
as a range. In the case of reserves, and where appropriate, this range of uncertainty can be reflected
in estimates for proved reserves (1P), proved plus probable reserves (2P), and proved plus probable
plus possible reserves (3P) scenarios. For other resource categories, the terms low estimate, best
estimate, and high estimate are recommended.
The term best estimate is used as a generic expression for the estimate considered to be the closest to the quantity that will actually be recovered from the accumulation between the date of the
estimate and the time of abandonment. If probabilistic methods are used, this term would generally
be a measure of central tendency of the uncertainty distribution. The terms low estimate and high
estimate should provide a reasonable assessment of the range of uncertainty in the best estimate.
For undiscovered accumulations (prospective resources) the range will, in general, be substantially greater than the ranges for discovered accumulations. In all cases, however, the actual range
will be dependent on the amount and quality of data (both technical and commercial) available for
that accumulation. As more data become available for a specific accumulation (e.g., additional wells
and reservoir performance data) the range of uncertainty in the estimated ultimate recovery for that
accumulation should be reduced.
The low estimate, best estimate, and high estimate of potentially recoverable volumes should
reflect some comparability with the reserves categories of proved reserves, proved plus probable
reserves, and proved plus probable plus possible reserves, respectively. While there may be a
significant risk that sub-commercial or undiscovered accumulations will not achieve commercial
production, it is useful to consider the range of potentially recoverable volumes independently of
such a risk.
3.3.2 ConventIonAl Petroleum
At the present time, several countries are recognized as producers of petroleum and have available reserves. These available reserves have been defined (Campbell, 1997), but not quite in the
manner outlined earlier. For example, on a worldwide basis the produced conventional crude oil
is estimated to be approximately 784 billion (784 × 10 9 ) bbl with approximately 836 billion bbl
remaining as reserves. It is also estimated that there are 180 billion bbl, which remain to be discovered with approximately 1 trillion (1 × 10 12 ) bbl yet to be produced. The annual depletion rate
is estimated to be 2.6%.
In addition, the crude oils available today to the refinery are quite different in composition and
properties to those available some 50–60 years ago. The current crude oils are somewhat heavier
insofar as they have higher proportions of nonvolatile (asphaltic) constituents. In fact, by the standards of yesteryears, many of the crude oils currently in use would have been classified as heavy
feedstock, bearing in mind that they may not approach the definitions used today for heavy crude
oil (Chapter 1). Changes in feedstock character, such as this tendency to heavier materials, require