Page 470 - Enhanced Oil Recovery in Shale and Tight Reservoirs

434 Enhanced Oil Recovery in Shale and Tight Reservoirs

pressure, and DSC tests should serve the purpose. In addition, the linear
relationship shown in Fig. 13.20 may not be extended to very high partial
pressures, probably up to several hundred of kPa for liquid oil, even much
lower for gas phase (Freitag and Verkoczy, 2005). If extended to a very
high partial pressure, the heat released will be unrealistically high.
Bae (1977) and Li et al. (2006) observed that the pressure effect is more
enhanced in LTO. However, Yoshiki and Phillips (1985) and K€ok and
Gundogar (2010) observed that increased pressure did not affect the activa-
tion energy in LTO but in HTO (K€ok and Gundogar, 2010). Burger and
Sahuquet (1972) found that the reaction order of oxygen partial pressure
for forward combustion should be less than one by comparing experimental
data with simulation data.

13.4.2.2 Catalytic effect of additives
It has been observed that clay minerals can have catalytic effect by reducing
activation energy for both LTO and HTO (Vossoughi et al., 1983; K€ok,
2006; 2012; Sarma and Das, 2009; Huang et al., 2016a), while Jia et al.
(2012a) observed slightly increased activation energy in LTO. The clays
include kaolinite, smectite, illite, chlorite, and shale cuttings which have
clays, with smectite having the strongest catalytic effect (Jia et al., 2012b).
Pu et al. (2015) observed that adding metallic CuCl 2 reduced activation en-
ergy in LTO and HTO. Burger and Sahuquet (1972) claimed that metallic
derivatives of copper, iron, nickel, vanadium, etc. reduced activation energy
and formed more coke. Huang and Sheng (2017a) surveyed 25 cases on the
effect of additives and found that the activation energy values were 26 and
73 kJ/mol for LTO and HTO, respectively, as shown in Fig. 13.21.
Compared with those (33and 107 kJ/mol for LTO and HTO, respectively)
in Fig. 13.7, they are lower, but the activation energy for LTO is not
significantly lower. More fuel is available in the presence of clay for
oxidation reactions. This may be caused by adsorption of hydrocarbons
on the clay surface and, hence, low distillation and pyrolysis in porous media
(Fassihi et al., 1984).

13.4.2.3 Gas phase versus oil phase
The gas phase has significant amount of vaporized light hydrocarbons with
two to six carbon atoms which are aliphatic, and it has much less antioxidants
(oxidation inhibitors); the oxygen diffusion into a gas phase is much faster
than into a liquid phase; therefore, the vaporized hydrocarbons will oxidize
much more quickly (Freitag, 2016).