Page 63 - Primer on Enhanced Oil Recovery

54 Primer on Enhanced Oil Recovery

Gas cap
Water
Rock and liquid drive Water
d
v
i
r
expansion drive drivee
Primaryy
P r i m a r
r
i
l

r
e
o
y
v
e
oil recovery
o
c
Depletion Combination Gravity drainage
drive drive
drive
Depletion drive +
Depletion drive + Gas cap drive +
Water drive
Water drive
Figure 7.1 Driving processes for the primary oil recovery stage.
Figure 7.2 Driving processes for the secondary oil recovery stage.

7.2 Secondary recovery

The secondary recovery of hydrocarbons involves the introduction of energy from
the outside into the reservoir through injection wells and the extraction of oil and
gas from extraction wells. Typically, secondary recovery of hydrocarbons involves
immiscible displacement by injecting water, gas or water-gas mixtures into injec-
tion wells (see Fig. 7.2). However, the most common fluid introduced by the reser-
voir to maintain its energy is water due to its availability and low cost.
As a rule, the introduction of secondary recovery in the early stages of reservoir
development even before the natural reservoir energy is depleted leads to a higher
oil recovery coefficient compared to the oil recovery coefficient obtained due to the
action of natural mechanisms during the primary oil recovery.

7.2.1 Waterflooding
Waterflooding is one of the major oil production techniques. It is estimated that
almost half of all produced oil is produced by use of waterflooding. Waterflooding
is carried out by pumping water into a series of injection wells and hydrocarbons
production through the production wells. Flooding, in general, is carried out to
achieve any of the following goals, or combinations thereof: