Page 65 - Primer on Enhanced Oil Recovery

56 Primer on Enhanced Oil Recovery

Figure 7.4 Contour water flooding injection well arrangements.

In reservoirs with an acute incidence angle, injection wells are positioned in the
dome for efficient displacement of oil. This system is known as arch flooding.
In all cases, the areal configuration of the injection wells and the distance
between the wells depend on several factors, which include rock and fluid charac-
teristics, reservoir heterogeneity, optimal injection pressure, planned development
period and economy.
The use of water flooding can increase the oil recovery ratio by 10 30%. The
criteria for the applicability of waterflooding are shown in Fig. 7.5.

7.2.2 Gas injection

The immiscible gas injection is carried out to maintain reservoir pressure, slow
down the production decline rate in the natural regimes of the reservoir and, some-
times, to support the gravity regime. An immiscible gas is usually injected with in
alternating pattern with water. For immiscible displacement, associated petroleum
gas, nitrogen or flue gases are used. The gas injected into the well behaves in the
same way as the gas in gas cap drive mode: the gas expands acting as a compressed