Once the residual oil contacts with the alkali in different conditions, different types of emulsions will be formed ; for example, the O/W type emulsion has lower viscosity which makes it easier to flow through the rock throat, hence improving the displacement efficiency
; the W/O type emulsion has higher viscosity which makes it easier to block the water channel, making part of the displacement fluid circumvent to unswept area, hence expanding the sweep volume.
Because the same viscosity is employed, the oil saturation reduction owing to the elasticity behavior of the polymer solutions, that is, the displacement efficiency
by viscoelastic polymer flooding, is higher than that of purely viscous glycerin flooding.
Meanwhile, as the polymer is viscoelastic, it can also improve the oil displacement efficiency
According to the statistical results of the oil displacement efficiency
of 1953 samples from 715 formations of 24 coring wells in an oilfield in a short period of time, the cumulative distribution curve of reservoir oil displacement efficiency
Preparing experiment setup was described in Figure 3: (I) preparing sand pack (properties are shown in Table 2); (II) injecting the brine with constant flow rate of 30 mL/h; (III) measuring each sand pack's tube output; (IV) calculating water absorption ratio and the oil displacement efficiency
in the sand pack's tube; (V) injecting prepared solutions with HPAM concentration 0.2% and Cr(III) crosslinking agent 0.2% for 0.3 PV at the same rate; (VI) 72 h shut in for gel forming (conditions identical with reservoir); (VII) injecting brine with the flow rate of 30 mL/h; (VIII) measuring the output of each sand pack's tube; (IX) calculating the water adsorption ratio and the oil displacement efficiency
It can reflect the pore size distribution and the fluid volume in different pores, which can quantitatively calculate the displacement efficiency
and residual oil in different pore size during water flooding oil.
Viscoelastic fluids demonstrating such behavior have been shown to improve displacement efficiency
and recovery yields compared with conventional Newtonian fluids.
The main purpose of adding polymer to the injected water is to decrease the mobility of the flood water by increasing its viscosity to improve the oil displacement efficiency
. Recently, it has been also proposed by several researchers [6-9] that the higher the elasticity of the polymer the higher the oil recovery.
Influence of Gas Species on Displacement Efficiency
. The results show that C[O.sub.2] breaks through at approximately 2 displaced volumes.
Fossil emission displacement efficiency
of 0.62 C:C (Puettmann and Lippke 2013),
These methods improve the sweep efficiency and the displacement efficiency
This mechanism may considerably improve water displacement efficiency
, and ultimately lead to higher oil recovery