Page 116 - Primer on Enhanced Oil Recovery

106 Primer on Enhanced Oil Recovery

ammonia, ethanol and ethylene plants. Power stations running on fossil fuel are
another good sources. All this is more than enough to meet the existing demand.
The most convenient source should be considered for each specific project to
ensure the economic efficiency of the injection project. Big gas quantities also
demand an adequate form of transportation.
The method of transportation from the source to the oil field depends on the
phase state of the carbon dioxide. Liquid requires smaller physical volumes but dic-
tates right combination of temperature and pressure. At low injection rates (up to
0.2 million cubic meters per day), the least expensive method of transportation is to
transport carbon dioxide as a liquid using existing insulated steel containers at a
pressure of 2 MPa and a temperature of 0 F(217.8 C). For large long-term pro-

jects, it is better to transport CO 2 by pipeline in a gaseous state (at a pressure of
10 14 MPa which is somewhere above 100 atm). The conditions then ensure a
single-phase flow.
The minimum mixing pressure needs to be experimentally determined for all
reservoirs. Combination of all available data then allows to assess technological
and economic efficiency of the method for a particular field and to begin the
implementation.
There are several modifications of the enhanced oil recovery method by injection
of carbon dioxide. Probably the less technologically demanding is an injection of
carbonated water.
Injection of carbonated water is the easiest way to implement the method is to
dissolve 3 5% CO 2 in water and then inject the carbonated water into the forma-
tion (see Fig. 10.10). On the first place there is oil displacement by slightly more
viscous water. At the same time good solubility of carbon dioxide in oil ensures its
transfer from water solution to the oil remaining behind the displacement front. As
a result, the interfacial tension between oil and carbon dioxide is significantly
reduced, the volume of oil increases, the viscosity decreases, and the phase

Figure 10.10 Injection of carbonated water.