After primary and secondary production stages of oil wells enhanced oil
recovery (EOR) methods should be used to increase and stabilize the uplift.
EOR methods include thermal, gas, chemical and physical technologies and
hydrofracturing. The technologies are usually based on decreasing the
interfacial forces in pores within the rock formation and reducing the viscosity
of the fluid. Each of these techniques has specific advantages and
disadvantages. That’s why the use of a concrete technique highly depends
on the geological characteristic and history of concrete fields. Many of the
mentioned above methods have been already used for decades. Currently
there is a big demand on new technologies in this field, which are applicable
also for wells which have been subjects of EOR in the past and for wells with
high-viscous and heavy oil. This is based on the fact that the categorization
of the reserves is deteriorating constantly. This chapter deals with the novel
methods in the field of EOR analyzing their advantages over the old
technologies and the new opportunities provided by them. The main attention
in this chapter is paid to the most promising technologies of hydrofracturing
and the ultrasonic technology of EOR, which showed very good results in
the last decade
THERMAL EOR PROCESSES
The influence of thermal EOR methods on the formation is the highest.
When these methods are applied, the reservoir is affected by thermal energy,
which is transported by thermal carriers or released directly into the
reservoir during exothermic chemical reactions (combustion). Often this
technology is used simultaneously to hydro- and thermodynamic methods.
Thermal EOR is accompanied by radical changes in physical and chemical
parameters of oil, a variety of phase transitions, etc. For example, when
the oil is heated from 25°C to 120°C, its viscosity decreases from 500-1000
mPa.s to 5-20 mPa.s. Apart of high temperature the reservoir is also
affected by high pressure.
Thermal EOR is used in cases with the most difficult physical and
geological conditions. These methods can be used to extract oil with the
viscosity up to 1000 mPa.s and natural bitumen. In case of thermal EOR 30-
58% of oil can be recovered. The following thermal EOR methods are
currently used:
- In-situ combustion
- Continuous steam drive
- Hot water drive
- Cycling steam injection
- Combined thermochemical treatment
