Page 63 - Fundamentals of Enhanced Oil and Gas Recovery

Screening Criteria of Enhanced Oil Recovery Methods 51

2.3.4.2 Alkaline Surfactant Polymer Flooding
Surfactant and alkaline reduce the IFT, and polymer assists in the sweep efficiency. In
the recent years, it is generally believed that alkaline surfactant polymer (ASP)
flooding is the most complex chemical method in which the cons are more than the
pros because of the scale and precipitation formed due to the alkaline. Large cases
were only implemented in China and Canada after 2005 [49]. Even with the recovery
factor of 25% original oil in place (OOIP), still the complex interaction between the
alkaline and reservoir rock and treatment of produced fluids remains as a great
difficulty.
The screening criteria have been changed in past decade for ASP flooding. Limit
of oil viscosity was updated as 1000 cp, while it was around 200 cp for ASP flooding
for a long period of time [50,51]. Polymer maintains the temperature limit in ASP

flooding, while new polymers can tolerate temperatures up to 100 C [52]. Recently,
some new surfactants have been proposed for high-temperature wells up to 200 C

[53]. Lithology is another screening criteria which changed over time. ASP flooding
were mostly used in sandstone reservoirs, but in Saudi Arabia and West Texas (United
States), this method was used in carbonate reservoirs [40,41]. Other criteria such as
permeability, acid content, and low salinity water (low concentration of divalent
cations) are still the same as before. West Kiehl, Sho-Vel-Tum, and Tanner fields in
the United States [54 56], Daqing, Gudong, and Karamay in China [13,57,58], and
Viraj field in India [59] are some ASP projects that have been performed in the recent
two decades in sandstones.

2.3.4.3 Surfactant Polymer Flooding
Usually, in real field scale projects of surfactant flooding, the surfactant will finger to
the oil bank and decrease the sweep efficiency. The fundamental of surfactant and
polymer flooding were explained earlier in this chapter. One of the highlights of this
combination is excluding the alkaline and its complications in the treatment.
Therefore, if the oil price increases to a level at which chemical flooding is consid-
ered economical, surfactant polymer (SP) flooding is recommended prior other
methods.
In the SP flooding, the main screening criteria are temperature and salinity. The
formation water divalent ions should be less than 500 ppm, and the temperature limit
is less than 100 C, the same as all chemical flooding methods which contain polymer.

The limitation on oil viscosity is less than 35 cp as proposed by Taber [8]. However,
other criteria like permeability are believed to be higher than 50 mD (compared to
Taber value that is 10 mD) [60]. It is noted that these values are not universally
agreed. Detailed screening criteria based on chemical EOR method is presented in
Table 2.1. It is worthwhile to note that the parameters reported in the table have been
determined based on four field scale projects.