23
Role of Water in Recovery and Production of Raw Fuels
This process generally recovers only 5%–15% of the oil from a well. Secondary oil
recovery process, often involving pumping water down (water flooding) the well to
maintain pressure on the oil, may increase the recovery to 30%. EOR techniques can
increase the proportion of the oil brought to the surface to 60%. When the well is
aged, the recovery of the remaining oil particularly requires the implementation of
EOR techniques [16,17].
Fundamentally, three types of EOR processes are currently being used: (1) miscible displacement processes that use miscible hydrocarbons, carbon dioxide, or inert
gas; (2) chemical processes that use surfactant polymer, polymer, or caustic solutions in water; or (3) thermal processes that use steam stimulation, steam flooding,
hot water injection, or in situ combustion. In this chapter, we focus on the latter two
processes because they use water or steam. Various methods used for EOR processes
are described in two excellent books and numerous articles by Speight [16,17]. The
present description closely follows his work along with other works reported in few
additional publications [13–15].
2.3.1 ChemiCAl ProCeSSeS
In general, due to their high cost, complex technology, and high risk, chemical flood
processes account for <1% of the total tertiary recovery. The successful chemical
processes for oil recovery require floodwater of precise salinity. Fundamentally,
three types of chemical solutions—surfactant–polymer solution, polymer solution,
and caustic alkaline solution—are used. Here we briefly describe the effectiveness
of each of these processes.
2.3.1.1 surfactant–Polymer solution (microemulsion Flooding)
The injection of surfactant–polymer solution is a two-step process [16,17]. The
first step is the injection of a surfactant slug commonly referred as either micellar
solution or microemulsion. The purpose of the surfactant is to displace oil that
cannot be displaced by water alone. The second step is the injection of polymer
mobility buffer. The polymer provides mobility control for a more piston-like
displacement.
In microemulsion flooding process, a stable solution of oil, water, electrolytes
of salts, and one or more surfactants are injected into the formation that is then
displaced by mobility buffer solution, which in turn is displaced by injection of
water. Two approaches can be used in microemulsion flooding. In one approach,
a relatively low-concentration (2–4 wt%) surfactant microemulsion is injected in
large pore volumes of 15%–60%. In the second approach, a high-concentration
(8–12 wt%) surfactant microemulsion is injected in a relatively small pore volume
from 3% to 20%. As the time passes, the second approach merges with the first
approach due to the dilution effect. Mobility control is important in the success
of this process [16,17].
Microemulsion technique can be applied over a wide range of operating conditions. In microemulsion flooding, the slug must be designed for specific reservoir
conditions of temperature, resident water salinity, and crude oil type. The success
of the microemulsion–polymer flooding in a given reservoir depends on the proper