Page 120 - Primer on Enhanced Oil Recovery

110 Primer on Enhanced Oil Recovery

Figure 10.14 Oil displacement schemes for immiscible hydrocarbon gas injection.

Increased oil volume (swelling);
Reduced oil viscosity.

10.2.1 Process mechanisms
Processes during hydrocarbon injection depend on the formation conditions and oil
composition. It is well known that full mixing is only achieved through formation
or intermediate zone where both injected hydrocarbons and oil undertake compo-
nents exchange until the difference between the two complete disappear. In the
absence of mixing zone the oil display network happens without mixing.
The processes without mixing are shown on Fig. 10.14. In order to emphasize
the processes the oil is split into three components: light oil with dissolved gas,
intermediate components and heavy fraction.
Low pressure injection has very limited gas dissolution in oil. It is possible to
see that beyond the displacement front oil saturation is only reduced to a certain,
still quite high level. The composition of remaining oil is not very different from
the original oil in place.
High pressure injection leads to much lower remaining oil saturation after the
displacement front as compared to low pressure injection. This low saturation is
provided by few essential processes:

the injected at high pressure gas has higher viscosity than the gas at low pressure;
there is partial dissolution of injected gas which leads to reduction of oil viscosity;
the oil is slightly swollen by the dissolved gas;