Page 356 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Forced imbibition 329

Table 11.9 Effect of pressure gradient by changing fracture permeability and
injected water viscosity.
Surfactant Alkali
(dp/dl) f , (dp/dl) f ,
Fracture permeability, mD psi/ft RF, fraction psi/ft RF, fraction
2000 0.132 0.0132 0.214 0.0300
20 13.209 0.0135 21.683 0.0263
2 134.281 0.0178 215.826 0.0284
Injected water viscosity, cP dp/dl, psi/ft RF, fraction
1 0.132 0.0132
10 1.274 0.0143
100 12.681 0.0105

effect, the fracture permeability is reduced in shale models with surfactant
and alkaline flooding. Table 11.9 shows that as the fracture permeability is
reduced to 2 mD, the pressure gradient is increased to 134.281 psi/ft in
surfactant flooding. Such pressure gradient is too high in actual flooding
cases in reservoirs. Even so, the oil recovery factors by 9 days of flooding
are increased from 0.0132 to 0.0178 only, with the absolute recovery being
practically insignificant. A similar observation can be made for the alkaline
flooding from this table. Parra et al. (2016) proposed to increase microemul-
sion viscosity to increase the transverse pressure gradient from fracture to
matrix for improved oil recovery in fractured reservoirs. This idea is tested
in the shale models here. In the base case, the injected water viscosity is
1 cP. The viscosity is increased to 10 and 100 cP so that the pressure gradient
is increased to 1.274 and 12.681, respectively. However, the absolute oil
recovery factors shown in Table 11.9 are practically insignificant.
Parra et al. (2016) experimentally demonstrated that when the microe-
mulsion viscosity was increased, the resulting higher pressure gradient
improved oil recovery. In their experiments, the matrix permeability was
100e320 mD. Now we use our simulation models to verify their observa-
tion. By doing so, we can also verify whether our simulation models can
predict actual performance in chemical flooding. The base shale model is
used to change the matrix permeability to 100 mD, and increase the water
viscosity from 1 cP in the base model to 10 cP. The results are presented in
Table 11.10. When the water viscosity is increased from 1 to 10 cP, the
resulting pressure gradient is increased from 0.145 to 0.675 psi/ft, and the
oil recovery factor is increased from 0.766 to 0.999. The incremental oil