Page 187 - Primer on Enhanced Oil Recovery

Forefront EOR 177

In some systems there is an opposite effect of shear rate the solution becomes
more viscous with the increase in shear rate. Again, there are complicated depen-
dencies on all parameters imaginable.
The particles not necessary to be a solid to create liquid with desired properties.
The “granularities” can be another liquid droplets or even gas bubbles. It is possible
to create carbon dioxide foam with some surfactant solutions. The foam has then
high viscosity and when injected improves sweep efficiency of the reservoir.
We have briefly discussed emulsions before. They are just another dispersed sys-
tem. Applying various methods and surfactants it is possible to create them for vari-
ous purposes of oil displacement and extraction. Sometimes the emulsions are
created in the production wells just by oil natural surfactants and then create pro-
blems for pumping.
Dispersed systems are very good advanced tool for EOR. The drawback is to get
read of dispersed matter and surfactants after oil has been extracted. Even breaking
water/oil emulsions is not exactly straightforward process. Interesting technologies
start to appear with time-limited systems, when the dispersed system disappears by
itself under reservoir conditions influence.

14.5 High pressure air injection (HPAI)

One active product is readily available for EOR air. It is possible to inject air at
a high pressure into an oil formation to achieve Enhanced Oil Recovery process.
Oxygen from the air oxidizes oil and essentially produces flue gas and water. Flue
gas then spreads through the reservoir mixing with oil and improving miscibility.
High oil recovery by the HPAI is provided by many positive processes happening
at the same time the pressure in the reservoir rises, the temperature goes up, vis-
cosity of oil drops, interfacial tension is reduced, oil swells due to carbon dioxide
absorption, the displacement driven in part by nitrogen and water. The method is
usually considered for light oil reservoirs as for heavy oil reservoirs in situ combus-
tion is preferred. The rock formation significantly affects the method performance
for many reasons. Also oil itself should preferably have low ignition temperature
and have high oxygen utilization at low temperature oxidation. It is worth remem-
bering that the oxidation process is faster at high pressure and this high pressure
should be created and maintained in the reservoir. Metal catalyst particles also can
be added to stimulate the oxidation process
The HPAI seems to be most attractive for recovery of tight oil. The method is
not limited to depth and can be used for deep reservoirs.

14.6 Renewable energy EOR

All processes during oil extraction and during Enhanced Oil Extraction need
energy. We have briefly outlined conventional energy sources for some EOR