Page 70 - Primer on Enhanced Oil Recovery

Oil recovery stages and methods 61

Figure 7.9 Additional Oil Recovery Factors (ORF) and Final ORF figures for the most used
EOR methods.

to formations containing heavy oils. Many projects so far have been implemented,
but only a few of them were commercially successful.
Fig. 7.9 shows the increase in oil recovery and final oil recovery figures, num-
bers (%) for the most used methods of enhanced oil recovery.

7.4 Sweep efficiency

The ultimate goal of enhanced oil recovery processes is to increase the overall oil
displacement efficiency, which is determined by microscopic and macroscopic effi-
ciency. Microscopic efficiency is provided on the scale of pores in the formation. It
is determined by the interaction of the displacing fluid with the rock, interfacial
forces and the fluid being displaced. For example, microscopic efficacy can be
increased by lowering capillary forces, changes in wettability and wedging
pressure.
Macroscopic or volumetric efficiency is observed on the scale of the entire for-
mation. The efficiency of volumetric displacement is determined by the displace-
ment efficiency both in the horizontal and in the vertical directions. It is also
depends on how effectively the injected fluid displaces the oil to the producing
wells. Figs. 7.10 and 7.11 show graphical representation of microscopic and macro-
scopic (horizontal and 3D sweeps).
The overall displacement efficiency of any oil displacement process can be
increased by improving the mobility ratio of the displaced and displacing fluids.
The mobility coefficient is defined as the ratio of the mobility of the displacing
fluid (i.e. water) divided by the mobility of the displaced fluid.