Page 160 - Primer on Enhanced Oil Recovery

150 Primer on Enhanced Oil Recovery

For injection of the polymer solution into the reservoir, it is necessary to have an
injection pressure much higher than the pressure during normal water flooding in
order to provide the necessary economically beneficial filtration rate and the rate of
field development. The injection might also need bigger injection well pipes and/or
more injection wells. In this regard, the implementation of polymer flooding in
reservoirs with low permeability may not be technically feasible.
The placement of wells in polymer flooding does not significantly differ from
conventional water flooding if the injection impact is effective and the design para-
meters of the field development are achieved: injection pressure-volume and oil
recovery rates. It should be noted that polymer flooding, usually in-circuit. Some
modeling also indicates that combination of horizontal injection and horizontal pro-
duction wells will be very beneficial.
It is accepted by the EOR application specialists that the polymer flooding is
most effective at the early stages of the oil field development. However, an early
implementation is usually hampered by the facts that at the early stage there is, usu-
ally, not enough information about the oil field geological structure and there are
no data on the field injectivity properties even by water. Both those uncertainties
usually delay polymer flooding implementation.

12.2 Alkaline flooding

Alkaline flooding includes the use of aqueous solutions of certain chemicals, such
as sodium hydroxide, sodium silicate, sodium carbonate and some ammonium com-
pounds. These solutions will react with some components in oil (in general terms
the affected compounds usually named saponifiable), in particular with organic
acids. The reaction products are surfactants chemical compounds which signifi-
cantly reduce the oil/water interfacial tension. Apart from this the oil recovery dur-
ing alkaline flooding occurs also emulsification of oil and changes in the rock
wettability. Some other compounds which can rise pH in the formation are also
used if the formation permeability is significantly affected by the sodium presence.
It is worth to say that an alkaline flooding only can be effectively applied in spe-
cific formations and for specific oils.
Changes in the interfacial properties of oil, water and rock in the process of alka-
line flooding have been known for long time. The first patents on alkaline water-
flooding appeared in the 20s of the last century, and practical application was
carried out at the Baku oil fields in the 40s. Already at the first commercial applica-
tion a high displacing capacity of alkaline water was found. In subsequent years,
interest in the alkaline flooding has increased significantly in connection with the
development of oil fields, when oil contains a significant amount of active polar
compounds.
Alkaline flooding is based on the interaction of the alkali molecules with organic
acids contained in the reservoir oil. As a rule, the emulsifying surfactants are
formed in this interaction. The produced surfactant (sometimes called soap) reduces