Page 158 - Fundamentals of Enhanced Oil and Gas Recovery

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this regard are centralized on optimization of fracture design, additives, and geome-
chanical solutions to poroelastic effects.

5.2.2.1 Underlying Technology
This process is composed of three stages, namely, injection, soaking, and production.
These are continuously repeated until oil production becomes economical without
gasification [2,19]. In this technique, the value of the residual oil is decreased by appli-
cation of various methods. Namely, reducing the viscosity, wettability changes, and
solution gas expansion [20] The schematic representation of this process is represented
in Fig. 5.2.
Moreover, many other products are generated due to chemical reactions includ-
inghydrogensulfide,carbondioxide, hydrogen during steam injection [22].These
are the result of decarboxylation of oil, conversion of S to H 2 S, and production of
H 2 ,CO,CH 4 ,and CO 2 that yields from reaction between crude oil, water, and
the produced CO 2 as a result of carbonate decomposition and further reactions [2].
These produced gases create an additional driving force that is called gas drive.
Moreover, oil viscosity is reduced by increasing its mobility [2,23]. The results of
Hongfu et al. [22] study reveal that viscosity was reduced 28% 42% by applying
cyclic steam injection (CSI).
This process works best for formations thicker than 30 ft, and reservoirs do not
deepen than 3000 ft with porosity and oil saturation more than 0.3% and 40%, respec-
tively. The geological structure of the near wellbore is very important in this process.

Figure 5.2 Cyclic steam stimulation process [21]. Source: From United States Department of Energy.