Page 418 - Enhanced Oil Recovery in Shale and Tight Reservoirs

388 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 12.49 Stabilized oil rate versus invasion depth in an oil-wet chip.

decreased with invasion as shown in Fig. 12.49. Those preceding figures
show that when the invasion depth was shallower, the flow back efficiency
and stabilized oil rate for the water were higher than those for surfactants.
This is because the surfactant reduced the capillary pressure gradient; but
as the invasion depth became deeper, the surfactant-reduced IFT resulted
in higher capillary numbers (in the order of 10 4 vs. 10 5 for water in
the Tangirala and Sheng’s (2018) experiments), and the flow efficiency
was improved compared with water.
The preceding results and conclusions in oil-wet chips were verified by
core flooding results (Tangirala et al., 2019). For the same fixed invasion
depth, the remaining (residual) oil saturation (S w2 ) at the end of flow back,
the flow back efficiency (flb), and the stabilized oil rate (Q o ) were compared
for water flooding with and without a surfactant. The following parameters
X, Y, and Z were defined:

ðS w2 Þ ðS w2 Þ
water surf
X ¼ (12.7)

ðS w2 Þ water ðS w2 Þ surf max
ðflbÞ surf ðflbÞ water
Y ¼ (12.8)
ðflbÞ ðflbÞ
surf water max
ðQ o Þ ðQ o Þ
surf water
Z ¼ (12.9)
ðQ o Þ ðQ o Þ
surf water max