Page 30 - Primer on Enhanced Oil Recovery

Hydrocarbon and oil reserves classification 21

deposits, forecasting the expected flow rates for various development project
strategies.
Methods of geological and hydrodynamic simulation (e.g. modeling) integrate
all the stages of geological, geophysical, petrophysical and industrial exploration of
the formation and its reserves. The already developed modeling software has been
widely used and applied to the reservoirs where a more accurate idea of the spatial
distribution of fluid and reservoir properties is required, both in terms of area and
deposit.
The development of new software packages continues. The modeling and soft-
ware development encircle the entire spectrum of research and production for a
field resource potential. The modeling is ranging from calculating reserve volumes
to assess development risks to optimizing various reserve development scenarios.

2.4 Oil recovery factor

The development of an oil and gas field is a continuous process involving various
stages of exploration and development. Each stage is characterized by a certain
degree of geological, geophysical and field explorations of the formation. All this,
in turn, defines the methodological approach to the calculation of reserves and, in
turn, affects the reliability of reserve calculation. It is well known that the reserve
assessment accuracy decreases in absence of actual geological and geophysical
information at the initial stage of exploration and especially in situations of signifi-
cant variability and heterogeneity of geological and field parameters of hydrocarbon
deposits.
It should be noted, that in defining the strategy for the development of hydrocar-
bon deposits one needs to take into the account the initial geological hydrocarbons
reserves. Environmental protection should be taken into the account together with
the amounts of hydrocarbons (recoverable reserves) which can be produced on the
basis of geological, technological and technical capabilities of the development
project.
The recoverable part of reserves (oil, gas, and condensate) is defined by intro-
ducing the recovery factor (RF). For oil it is called oil recovery coefficient, for gas
and condensate, respectively, gas recovery coefficient and condensate recovery.
The oil recovery factor (at the particular time) is defined as the ratio of the value
of recovered reserves (Q rec ), that is, already extracted to the surface, to the value of
geological reserves (Q geol ) located in the depths of the deposit:

RF 5 Q =Q geol (2.5)
rec
Oil recovery from reservoirs (ORF) has a significant effect on the projected
(planned) volumes of capital investments in the process of developing hydrocarbon
deposits, as well as on the likely estimate of the growth of industrially recoverable
reserves. The accuracy of oil recovery determination has a direct impact on the