Page 127 - Primer on Enhanced Oil Recovery

Gas flooding 117

Figure 10.22 Gas injection well design.

mechanical impurities and compressed. Gas cleaning can be done with oil or
cyclone dust collectors, as well as gravity separators. To compress gas, it is neces-
sary to install a compressor station, the capacity of which is calculated from the
required volume of hydrocarbon gas and injection pressure. If high-pressure gas is
present in the field, injection can be carried out in an uncompressed manner, which
significantly reduces capital and operating costs.
The injection of hydrocarbon gases is carried out through a separate tubing,
which is usually lowered to the upper holes of the well filter. The annular space is
blocked by a drilled packer, which is lowered onto the well. This protects the casing
from high gas injection pressure. The design of the injection well is shown on
Fig. 10.22.
A serious problem with the technology implementation is events of gas break-
throughs in the production wells. To prevent a breakthrough, it is necessary to con-
trol the gas injection rate, the gas factor and the composition of the produced gas.
In case of a breakthrough it is essential to stop it. For this it is possible to lower
fluid withdrawal from the wells.
Modifications to the method can be applied to reduce the consumption of valu-
able hydrocarbons. For instance, after injecting the slug of enriched gas in a volume
enough to effectively displace the oil, it is possible to inject cheaper gases. For