Page 129 - Primer on Enhanced Oil Recovery
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Gas flooding 119
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The disadvantages include the low solubility of nitrogen in oil (35 45 m /m 3
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for light oil and 15 25 m /m for heavy oil). The solubility of flue gases is not so
different from nitrogen as the gas consists by almost 90% percent of nitrogen. The
minimum mixing pressure for nitrogen exceeds 35 MPa, which is significantly
higher than for natural gas (25 MPa) and carbon dioxide (8 MPa).
10.3.1 Process mechanisms
Depending on the oil type, reservoir conditions and the injected gas type (composi-
tion) an oil/gas front propagation and interaction can proceed in evaporation mode
or in condensing gas mode.
10.3.2 Applicability criteria
Miscible displacement during injection of nitrogen and flue gases only should be
carried out in deep oil deposits. The reason was outlined just before mixing is
only achieved at high pressures.
The displacement front has unfavorable mobility ratio. For this reason, as with
the injection of hydrocarbon gases, the provision of gravitational stabilization of the
displacement front is only possible in steeply falling oil strata. The criteria for the
applicability of the method are shown in Fig. 10.23.
The disadvantages of the method include:
viscous instability leads to low vertical and horizontal formation sweep efficiencies;
corrosion can cause problems during flue gas injection;
Figure 10.23 Screening parameters for nitrogen and flue gases injection.
