Page 200 - Fundamentals of Enhanced Oil and Gas Recovery

188 Mohammad Ali Ahmadi

Chemical flooding methods

Alkaline
surfactant Surfactant Polymer Alkaline Nano fluid
polymer flooding flooding flooding flooding
flooding

Figure 6.1 Classification of chemical EOR methods. EOR, enhanced oil recovery.

the reservoir [7,8], and to increase the viscosity of the injected water to increase the
sweep areas in the reservoir [9], and alkaline and surfactant flooding to create low
oil water interfacial tension (IFT) and hence remobilizing the trapped oil [10,11].It
is also possible to enhance the oil production through wettability alteration of the
reservoir rock during a surfactant flooding [10 14]. Fig. 6.1 depicts the classification
for chemical EOR methods.
As an example of chemical EOR, surfactant flooding is to lower the IFT, which
causes lower capillary pressure and enhances the imbibition mechanism by gravity
drive in oil-wet reservoir [13]. The concept behind the chemical-based EOR meth-
ods is increasing the capillary number; the number is dimensionless representing the
ratio of viscous forces over capillary forces. The capillary number can be expressed
through the following equation [15 17]:
vμ
N C 5 (6.1)
σ
where v represents the fluid velocity, μ denotes the fluid viscosity, and σ is the IFT.
There are different relations between the residual oil saturation and capillary number
in the depleted oil reservoir. Fig. 6.2 illustrates the typical variation of residual oil sat-
uration versus capillary number reported in literature [17].

6.2.1 Surfactant Flooding
Ahmadi and Shadizadeh [19] carried out comprehensive series of core-flooding
experiments on real carbonate rocks to examine the efficiency of a new natural surfac-
tant for EOR goals. They conducted core-displacement test along with IFT measure-
ment to determine the efficiency of the surfactant in terms of oil recovery factor.
They discussed that the surfactant extracted from Ziziphus spina-christi could consider-
ably increase the oil recovery factor. Besides this advantage, there is no environmental
issue using such a surfactant [19].
Ahmadi et al. [20] proposed an environment-friendly surfactant extracted from
mulberry leaves. They conducted different experiments under reservoir condition to