24
Water for Energy and Fuel Production
assessment of the characteristics such as the nature of oil and water content, relative
permeability, mobility ratios, formation fractures and variations in permeability,
porosity, formation continuity, and rock mineralogy [16,17].
2.3.1.2 Polymer solution
The addition of polymers in water increases the solution viscosity, thereby increasing
the sweep efficiency. Two classes of polymers are normally used: polyacrylamides
(PACs) and polysaccharides (PSAs). PAC (normally used in 50–1000 ppm concentration) decreases the mobility of the injected fluid by decreasing the permeability
of the reservoir rock. Addition of PSA, however, increases the viscosity with a very
low level of permeability reduction in the reservoir rock. The high viscosity of both
solutions compared to water results in a significant long-range oil production.
Polymer flooding is most effective for heterogeneous reservoirs because they respond
favorably to the improved vertical sweep efficiency. This technique is also preferred over
microemulsion flooding for recovery of more viscous oils. Currently, polymer flooding is
being used in a significant number of commercial field projects [16,17].
The injection of polymer solutions may face stability problems due to oxygen
contamination. For PAC solutions, this may be alleviated using sodium hydrosulfite
in low concentrations. In general, the degradation of polymer due to mechanical,
chemical, thermal, and microbial reasons can be totally prevented by using specialized equipment or techniques [16,17].
2.3.1.3 Caustic alkaline solution
This method is inexpensive and preferred, but it provides low productivity. In this
method, inorganic alkaline chemicals such as sodium hydroxide, sodium carbonate,
or sodium orthosilicate are added to the water to enhance oil recovery by one or
more of the following mechanisms: (1) interfacial tension reduction, (2) spontaneous
emulsification, or (3) wettability alteration. For an efficient oil recovery, the pH range
12–13 is optimum. Sometimes the mobility ratio can be improved by an addition of
polymer in the alkaline solution [16,17].
2.3.2 ThermAl ProCeSSeS
Thermal EOR processes are very popular and gaining more use due to the fact
that they can be applied to both conventional and unconventional oil recovery.
Three types of thermal processes are currently used: steam stimulation, hot water
injection, and in situ combustion. We briefly examine each of these processes in
Sections 2.3.2.1–2.3.2.3.
2.3.2.1 steam stimulation
Steam stimulation is a general term used when steam is injected into a well and then
produced back out of the same well. The method is also referred as cyclic steam
injection, steam soak, or huff and puff. The process uses up to 1000 bbl of water
per day (in the form of superheated steam) for 10–30 days and then the well is shut
in for about 1–4 weeks to allow the steam to soak in the well [16,17]. During this
soaking period, heat dissipates into the reservoir and reduces the viscosity of oil
Water for Energy and Fuel Production
assessment of the characteristics such as the nature of oil and water content, relative
permeability, mobility ratios, formation fractures and variations in permeability,
porosity, formation continuity, and rock mineralogy [16,17].
2.3.1.2 Polymer solution
The addition of polymers in water increases the solution viscosity, thereby increasing
the sweep efficiency. Two classes of polymers are normally used: polyacrylamides
(PACs) and polysaccharides (PSAs). PAC (normally used in 50–1000 ppm concentration) decreases the mobility of the injected fluid by decreasing the permeability
of the reservoir rock. Addition of PSA, however, increases the viscosity with a very
low level of permeability reduction in the reservoir rock. The high viscosity of both
solutions compared to water results in a significant long-range oil production.
Polymer flooding is most effective for heterogeneous reservoirs because they respond
favorably to the improved vertical sweep efficiency. This technique is also preferred over
microemulsion flooding for recovery of more viscous oils. Currently, polymer flooding is
being used in a significant number of commercial field projects [16,17].
The injection of polymer solutions may face stability problems due to oxygen
contamination. For PAC solutions, this may be alleviated using sodium hydrosulfite
in low concentrations. In general, the degradation of polymer due to mechanical,
chemical, thermal, and microbial reasons can be totally prevented by using specialized equipment or techniques [16,17].
2.3.1.3 Caustic alkaline solution
This method is inexpensive and preferred, but it provides low productivity. In this
method, inorganic alkaline chemicals such as sodium hydroxide, sodium carbonate,
or sodium orthosilicate are added to the water to enhance oil recovery by one or
more of the following mechanisms: (1) interfacial tension reduction, (2) spontaneous
emulsification, or (3) wettability alteration. For an efficient oil recovery, the pH range
12–13 is optimum. Sometimes the mobility ratio can be improved by an addition of
polymer in the alkaline solution [16,17].
2.3.2 ThermAl ProCeSSeS
Thermal EOR processes are very popular and gaining more use due to the fact
that they can be applied to both conventional and unconventional oil recovery.
Three types of thermal processes are currently used: steam stimulation, hot water
injection, and in situ combustion. We briefly examine each of these processes in
Sections 2.3.2.1–2.3.2.3.
2.3.2.1 steam stimulation
Steam stimulation is a general term used when steam is injected into a well and then
produced back out of the same well. The method is also referred as cyclic steam
injection, steam soak, or huff and puff. The process uses up to 1000 bbl of water
per day (in the form of superheated steam) for 10–30 days and then the well is shut
in for about 1–4 weeks to allow the steam to soak in the well [16,17]. During this
soaking period, heat dissipates into the reservoir and reduces the viscosity of oil