Page 31 - Primer on Enhanced Oil Recovery

22 Primer on Enhanced Oil Recovery

assessment of residual reserves, the effectiveness of the development systems used,
the prospects and scale of the introduction of new hydrocarbon production technol-
ogies, and the timing of the commercial development of deposits.
An increase in the oil recovery coefficient of at least 0.01 (a very minor amount)
in its economic significance is equivalent to the discovery and commissioning of a
new field in industrial development. Solving the problem of achieving the highest
possible oil recovery ratio is one of the most urgent objectives of petroleum geol-
ogy and the development of oil and gas fields.
The oil recovery factor calculated over the entire development period is referred
to as the ultimate coefficient (Ultimate Recovery Factor URF). Calculated over a
specific time period from the start of development to the evaluation date the cur-
rent RF.
Currently, several methods for calculating the final (expected) RF are widely
used:

The method of analogies makes estimations on the basis of the natural reserve oil driving
forces (Reservoir Drive Mechanisms);
Statistical method is built on the basis of obtaining dependencies between the final oil
recovery coefficient (RF) and various geological, physical and technological factors;
Coefficient method finds its roots in determining the values of a number of coefficients
when taking into account the geological and field characteristics of some specific oil
deposits and features of the planned development project;
Hydrodynamic method takes technological calculations of few reservoir development sce-
narios by modeling a specific hydrocarbon deposit.

Based on more than a century of experience in the development of hydrocarbon
deposits, it has been established that the oil recovery factors (RF) achieved as a
result of the implementation of projects vary in a wide range from 0.05 to 0.75 and
higher. The achievable value is mainly related to the application of secondary
(methods for maintaining reservoir pressure, i.e. injection of water into the reser-
voir) and tertiary (new methods of enhanced oil recovery of reservoirs EOR
enhanced oil recovery) production stimulation methods.
If RF reaches 40 50% or even higher then oil formations are classified as active
(for low-viscosity oil in highly permeable reservoirs). If RF not exceeds 10 30%
despite using traditional methods to displace oil from the porous medium, then the
reserves are called hard-to-recover (usually high viscosity of oil, or low-permeable
reservoirs, non-traditional collectors).
The coefficients of oil-gas-condensate recovery are determined on the basis of
technological and technical-economic calculations when compiling a project for the
development of a specific reservoir.
The magnitude of the projected RF depends on the complex geological, physical
and reservoir parameters. When all of this is determined by the lithological compo-
sition of reservoirs, the heterogeneity of the structure of the reservoir, permeability
and effective oil-saturated power, the manifestation of the deposit natural drives.
The methods (technologies) used in the extraction of hydrocarbons also have a
direct impact on the achievement of maximum oil recovery ratios. One can account