Page 52 - Fundamentals of Enhanced Oil and Gas Recovery

40 Amirhossein Mohammadi Alamooti and Farzan Karimi Malekabadi

layer is high enough, and there is a low oil viscosity. In such cases the recovery of oil
will be high.
Gas is usually injected in a point below the reservoir crest. Gravity causes the gas
to move upward and drives the oil towards the production well. If vertical permeabil-
ity is low, the process of gravity separation will not be completed. If the intensity of
oil production is more than the intensity of gravity separation process, the final recov-
ery of oil will decrease.

1.15.7.2 Water Injection
Water and oil are two fluids that are immiscible. When these two fluids are situated
side by side in the pores of a rock, they separate from each other according to their
wettability. In other words, water usually sticks to the rock and separates and moves
the oil. Given the existent forces, oil moves in a massive form until it is trapped in a
location where its permeability is almost zero. Then over time, the phases of water
and oil are separated completely, and due to the difference between the density of
water and oil, water moves below the oil.
Flooding efficiency is dependent on several variables, the most important of which
include the degree of oil saturation during the initiation of flooding, the saturation
degree of the residual oil, water saturation degree, the saturation degree of free gas at
the start of injection, the volume of floodable pores, oil and water viscosity, effective
permeability of oil in nonmobile residual saturation, “and relative permeability of
water and oil.

REFERENCES
[1] D.W. Green, G.P. Willhite, Enhanced Oil Recovery, SPE Textbook Series, vol. 6, 1998
[2] T.B. Jensen, K.J. Harpole, A. Osthus, EOR Screening for Ekofisk, SPE 65124, Presented at the 2000
SPE European Petroleum Conference Held in Paris, France, 24 25 October, 2000.