Page 166 - Primer on Enhanced Oil Recovery

156 Primer on Enhanced Oil Recovery

Figure 12.11 Alkaline-polymer-surfactant flooding.

In addition to this, just alkali injection method, there are numerous, more
advanced and more expensive options for the implementation of alkaline flooding.
One of them is to inject a polymer solution slug with after the alkaline solution to
control mobility and improve displacement efficiency (see Fig. 12.11). It is more
expensive and technologically more challenging option but it can be viewed as eco-
nomically justified. Due to the complexity of mineralogy and lithology of oil reser-
voirs, the probability of a reaction between an alkaline solution, salt water and oil
is significant under reservoir high temperature and high pressure conditions. In this
regard, the choice of the appropriate injection system for specific oil field condi-
tions is very important for obtaining the best results.
In modern implementations of alkaline flooding, alkaline agents are used in com-
bination with low concentrations of synthetic surfactant and polymer solution slugs
to control mobility.
Rather different method of alkaline flooding was first implemented in the former
USSR, in 1976, at the Trekhozernoye deposit. This method includes the pre-
injection of freshwater, the injection of hard reservoir water (connate water) and
alkaline solution. As a result of the sedimentation reaction between the alkaline
solution and the hard formation water, the permeability of the highly permeable
parts of the formation decreases and the formation coverage of the formation
increases. Periodic, cyclic pumping of liquids in the specified sequence is also pos-
sible (Fig. 12.12).
Usually for the preparation of alkaline solutions the following chemicals are
used:

caustic soda, sodium hydroxide NaOH;
soda ash, sodium carbonate Na 2 С0 3 ;
ammonia HH 4 OH;
liquid glass, sodium metasilicate Na 2 SiO 3 .