Page 203 - Primer on Enhanced Oil Recovery

192 Primer on Enhanced Oil Recovery

Most often, rather simplified technical screening is used to select an enhanced
oil recovery method. In this case the analysis of geological and physical properties
is conducted on the principle of “suitable not suitable.” In many cases this simple
approach is most used as it is self-obvious and there is no need to use complex soft-
ware. The boundary values are taken from the so named Taber tables. Taber and
co-authors have in 1997 summarized the selection criteria for all major EOR techni-
ques. They had analyzed the application results and tabulated the main applicability
parameters. The authors identified 10 criteria values. Each criteria value is com-
pared with the corresponding values for the field of interest. Those criteria are: fluid
0
(oil) properties (API Gravity [ API], viscosity [cp]) and reservoir related properties
(oil saturation, oil strata thickness, location depth, temperature, pressure, porosity,
permeability, lithography). Slightly modified assessment set, by recognizing the
importance of the oil molecular composition for EOR application methods, can be
summarized as presented in Table 16.1.
A score is assigned between 0 and 1 for each criteria. Grade 1 is assigned when
the related property is within the recommended range and zero when it is not in this
range. When a property matches only part of a range, the score is assigned in pro-
portion to the matching rate.
Fig. 16.1 shows an example procedure for assigning scores. Using the deposit
example we need to consider the main screening criteria for some conditional EOR.
In this case all criteria with the exception of the permeability of the reservoir are
within the specified ranges of screening and they are assigned the value 1.
Permeability, as it is outside the recommended range, is assigned a proportional
score equal to 0.6666. Next, we find the arithmetic mean value of the assigned
points, which is 0.9524. Thus, the applicability of this method of EOR is 0.9524
points, i.e. quite high.

16.2 Phase behavior and core analysis

ToIn order to carry out full geological modeling, it is necessary to know the oil
physicochemical properties, character of the reservoir, oil strata configurations and
the reservoir rock filtration properties. For the complete understanding the geophys-
ical studies should be complimented with laboratory analysis of reservoir fluids and
core materials behavior at the reservoir conditions. All laboratory studies should be
conducted at reservoir pressure and temperature.

16.2.1 Physicochemical properties of reservoir fluids
Complex reservoir fluids behavior is understood on the basis of laboratory experi-
mental data and thermodynamic modeling. All this undertaking allows to predict
fluid behavior in the feasible range of Pressure, Volume and Temperature (PVT
coordinate space).