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The injected water should have a good ability to wash
oil from rock. For this purpose, conduct water treatment using
chemicals.

§4.2 MAINTENANCE OF RESERVOIR PRESSURE
BY GAS INJECTION

Pressure maintenance by injecting gas into the up
structure parts of the reservoir is most frequently used under
conditions naturally favouring the development of a solution gas
drive (low edge water activity, a small difference in reservoir
saturation pressure) and also when there is a natural gas cap.
Considering a pressure maintenance project with the
injection of gas into the up structure part of the reservoir, one must
evaluate the practical and economic advantages of the project in
each particular case. It must be borne in mind that reservoir
pressure, particularly in the initial period of production, may be
very high and costly equipment will be required to develop the
high pressures that are necessary for a successful operation. It is
also necessary to study carefully the geological conditions of the
reservoir. For the success of the operation the structure not be too
flat (the dip should preferably be not less than 12-15°); a low-
dipping structure has an adverse effect on the gravitational
separation of oil and gas.
It is desirable that the reservoir be uniform permeability
and the oil of low viscosity. In nonhomogeneous reservoirs and in
the presence of a large number of tectonic faults and fissures it is
difficult to control the movement of the gas through the reservoir
rock.
The best results are obtained when a pressure
maintenance project is started early. However, field practice shows
that gas injection can also be applied, though with less success,

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