Page 185 - Primer on Enhanced Oil Recovery

Forefront EOR 175

concentration near electrodes might produce overheating and in the overheated
zones there will be water evaporation at first and then reduction of the process effi-
ciency. To avoid this one electrode (or both electrodes) can be water injection or
the connate water re-injection well. Horizontal well drilling technology allows
installation of special heating cables precisely within the oil strata. The cables elim-
inate overheating problems and make the process very simple and economical.
This Ohmic method is very universal, its applicability is not limited by the reser-
voir geology, depth, pressure or temperature.
It is also possible to utilize inductive and microwave heating. In the first case, pro-
duction well tubing is heated at the oil strata level by a medium frequency induction
current. This allows to rise the temperature at the well adjoining zone and create flow
zone with significantly improved oil flow near the production well. Low oil viscosity
in this zone positively reflect on the general oil recovery. In the second case, micro-
wave antennas can be places at the strategic part of reservoir to rise temperature in
the zones with low permeability or reservoir temperature in general.
Electrical heating is usually consuming few times less energy than steam injec-
tion and has good potential to reduce the carbon footprint of the thermal EOR.
Compared to the conventional steam injection electrical EOR can be implemented
at any depth and does not depend on injectivity. It is also technically simple, less
dependant on chemicals supply chain and does not produce waste materials.

14.3 Advanced polymer systems

Polymer flooding is well established and used EOR technique. The limitations
come from the traditional polymer low robustness and the method sensitivity to the
reservoir conditions. This usually requires to employ higher polymer concentrations
to counterbalance the negative process sides. High polymer concentrations are more
expensive by themselves, more challenging to inject down the well and create pro-
blems with the reservoir injectivity.
Many advanced polymer materials are constantly developed for various pur-
poses. It is most useful for EOR to use polymers when the reservoir temperature
instead of degrading polymeric solution would increase the solution viscosity, at
least in some temperature range. In broad terms it is possible to talk about thermo-
viscosifying or thermo-thickening polymers. Additional benefit comes from the
lower, as compared to traditional polymer, molecular weight to achieve the same
viscosity. Additionally, some polymers from this class demonstrate low sensitivity
to water salinity. In fact, some of thermo-thickening polymers show increase of vis-
cosity at high salinity.
Other classes of new polymers will form nanoparticles at elevated temperatures,
this in turn will increase the solution viscosity. It is also possible up to extend to
use latent and delayed action polymerization systems.
All this allows, in principle, to manage highly permeable zones in stratified inho-
mogeneous reservoirs and to provide displacement in problematic areas. Injection