Eor methods

REPORT on EOR METHODS
Prepared by Lab. FIRP ULA Mérida Venezuela.
Contains some extracts from EOR Field data literature search L. Lake & M. Walsh, UT
and cited references. Cost information is posted in 2008.
All of currently available EOR is based on one or more of two principles: increasing the
capillary number and/or lowering the mobility ratio, compared to their waterflood values.Increasing the capillary number means, practically speaking, reducing oil-water interfacial
tension. The injectant mobility may be reduced by increasing water viscosity, reducing oil
viscosity, reducing water permeability or all of the above.
Using the nomenclature adopted by the Oil and Gas Journal, EOR processes are divided into
four categories: thermal, gas, chemical, and other. Table 2summarizes the main processes within
each category. The processes are typically defined by the nature of their injected fluid. For
instance, gas EOR includes hydrocarbon miscible/immiscible and CO2 miscible and immiscible
processes.

Gas EOR Methods
These methods are capillary number increasing methods. They are also called solvent flooding,
miscible-gas flooding or simply gas flooding. Theinjectant can be dry gas, enriched gas
(hydrocarbon miscible), CO2, nitrogen or flue gas, or combinations of these.

Solvent methods recovery oil by mass transfer. For some processes, the mass transfer of
intermediate hydrocarbon components is from the crude to the solvent (vaporizing gas drive) and
for others the transfer is from the solvent to the crude (condensing or rich gas drives). CO2,nitrogen or flue gas are vaporizing gas drives and hydrocarbon miscible drives are the latter. In
all cases it is the intermediate component, the component that is doing the transferring, that is
key.
If the reservoir pressure is large enough (or if there is sufficient intermediate content at the
current pressure), the mass transfer will result in a mixture that is miscible with the crude, inwhich case the predominant recovery mechanism is a miscible displacement.
In a miscible displacement, interfacial tension vanishes and capillary number becomes
infinite. Failing this, the displacement will be immiscible. Immiscible displacements are not as
efficient as miscible displacements but may still recover oil by swelling, viscosity reduction or
permeability increase, or pressure build up.CO2 and enriched hydrocarbons tend to be miscible
solvents; nitrogen and flue gas tend to be immiscible.
Miscible displacements in the laboratory result in nearly 100% ultimate oil recoveries. Fieldscale displacements recover much less, primarily because the solvent tends to be more mobile
that the oil/water mixtures they are displacing, which leads to bypassing of the solvent around orthrough the oil. Bypassing is the result of reservoir heterogeneity and viscous instability between
two fluid fronts. Some types of heterogeneity can result in substantial mixing in the reservoir and
a loss of miscibility.
The bypassing can be eliminated or at least reduced by co-injection of water with the solvent
(the WAG process), conducting the flood in a gravity stable mode and/or using foamsto reduce
the gas mobility.
Most of the reported results have been on CO2 solvent flooding in the US wherein ultimate
recoveries of 12% of the original oil in place and utilization factors of 10 MCF
solvent/incremental barrel of oil recovered are reported. These performances translate into
chemical costs of 10-30 $/incremental bbl, depending on performance, and the cost of the
solvent. Manypotential CO2 injection projects are on hold because of the lack of solvent.

Chemical EOR Methods
These methods are increasing capillary number processes (micellar-polymer,
caustic/alkaline) or mobility ratio processes (polymer). All are based on injecting one or more
chemicals into a reservoir to bring about the aforementioned changes.
Polymer Flooding.

Polymer methods consist of...