Page 19 - Primer on Enhanced Oil Recovery

10 Primer on Enhanced Oil Recovery

exist. In almost every oil-producing country there are also national classifications
(SORP, CSA, PRO, NPD, USGS, to mention just few).
In the 1990s European Economic Commission (EEC) began work to develop
and set universal standards to classify solid fuels and mineral reserves. Since 2004
the classification has been extended to hydrocarbons (natural gas and oil). At the
same time the classification was internationally adopted and renamed. Now it is
known as the United Nations Framework Classification of Fuels and Minerals
Stocks (UNFC).
The calculated volumes of hydrocarbons in the earth crust are regarded as
“reserves-resources”. The volumes are presented in open and unopened natural
deposits (recoverable and non-extractable resources and reserves), plus already
extracted hydrocarbons. Quantitative estimation of “resource reserves” is made by
calculating the total volume of hydrocarbons. Both, the identified deposits, with
geological proven oil and gas content, and in promising deposits, that are expected
to open in the future, are accounted for. The term “reserves-resources” refers to all
types of hydrocarbon raw materials that are currently referred to as “traditional” or
“unconventional” reserves. “Unconventional” refers to deposits of tight gas and oil
in solid sandstone, shale oil and gas, gas hydrate accumulations, and so on.
The assessment of reserves aim to get oil volume in barrels and gas reserve in
cubic feet or cubic meters. This is potential amount for commercial exploration.
Depending on the classification schemes and perceived uncertainties (risks) of
future production, hydrocarbons in the formation (oil fields) are grouped into differ-
ent categories, for instance: petroleum reserves; contingent resources and prospec-
tive resources (see Fig. 2.2).
One of the most widely used schemes for classification and management of
hydrocarbon reserves in the world is SPE-PRMS. This is mostly due to the fact that
the scheme takes into account the greatest number of variables (factors) during the
forecasted production. Also, the scheme makes the distinction between the main
categories of recoverable hydrocarbon reserves and resources, which include:
“Production”, “Reserves”, “Conditional resources” and “Prospective resources” as
well as “Unrecoverable” amounts of hydrocarbons.

Figure 2.2 Hydrocarbon reserve classification.