Page 343 - Enhanced Oil Recovery in Shale and Tight Reservoirs

316 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 11.6 Oil recovery factors from water injection only, surfactant injection only, al-
kali injection only, and their sequential injection for the sand rock.

injection or surfactant injection (Sheng, 2012; 2013a), these results indicate
that wettability alteration could be more important than IFT reduction.
The oil recovery factors from the water injection only, surfactant injec-
tion only, alkali injection only, and their sequential injection for the shale
rock are shown in Fig. 11.7. No oil can be produced from the water injec-
tion only, because the shale rock is oil wet; once litter invaded water leads to
a higher water saturation in the invaded blocks, the capillary pressure
becomes negative (refer to Fig. 11.2), so oil can hardly flow out. For the
surfactant injection only, the IFTs are reduced and the relative permeabilities
are increased. The high permeabilities in the fracture make the injected sur-
factant solution break through the producer, so that the oil in the matrix

Figure 11.7 Oil recovery factors from water only, surfactant only, alkali only injection,
and their sequential injection for shale rock.