Page 21 - Primer on Enhanced Oil Recovery

12 Primer on Enhanced Oil Recovery

An important element in calculating prospective resources is the determination of
risk or uncertainty, which must be calculated by probability theory.
Prospective resources are accessed by two probabilities - the likelihood of their
discovery and the likelihood of the development.
Prospective resources are classified according to the level of reliability deter-
mined during the assessment of recoverable resources. They are subject to their
finding and later industrial production, as well as good fitment into the stages of the
project development.
Unrecoverable resources are the part of the discovered and unexploited ini-
tial geological reserves and hydrocarbon resources (discovered or undiscovered ini-
tial-oil-in-place). The resources are accounted according to an estimate (as of a
specific date). The resources cannot be extracted in future development projects of
the formation.
However, a part of the specified amount of unrecoverable resources may
become recoverable in the future as the economic situation changes or new
extraction technologies are developed. Whatever left might remain in the reser-
voir and can be not recoverable due to geological, physical and chemical
constraints.
Estimated Ultimate Recovery (EUR) in the classification SPE-PRMS strict
interpretation is not a category of reserves and resources. However, this term can be
used to estimate (on a specific date) the amount of hydrocarbons potentially recov-
erable (extractable) from any exploited or untouched reservoir.
When conducting studies to assess the amount of resources in an oil containing
location and to denote total geological reserves and resources, alternative terms
such as Total Resource Base or Hydrocarbon Endowment can be used. Total
recoverable reserves or NIH may be referred to by the term “area potential”. Total
recoverable or EUR may be termed Basin Potential.
The sum of reserves, conditional resources and prospective resources, can also
be defined as the term “remaining recoverable resources”.
When using these terms, it is necessary to ensure that each of the components of
the Summing Stocks and Resources are consistent with the various degrees of tech-
nical and economic risk given the definitions in the SPE-PRMS classification.
The SPE-PRMS classification divides stocks into categories: “possible”, “proba-
ble” and “proved.”
Each category in practice lead to average successful extraction rate, as proven
by many already implemented projects and strict assessment criteria. “Proved” cate-
gory is extracted in 90% of cases. “Probable” reserves are extracted with 50%
susses. Only 1 in 10 cases is successful in extraction of “possible” category.
Proved reserves (P90) reserves that can be extracted under existing economic
conditions and applied technological processes, using probabilistic models, there
should be a 90% probability that the cumulative production will be equal to or
exceed the estimated reserves.
The proven reserves developed by Proved Developed Producing (PDP) will be
extracted from the developed reservoirs that have been discovered and are being
developed at the time of their assessment.