Page 409 - Enhanced Oil Recovery in Shale and Tight Reservoirs

380 Enhanced Oil Recovery in Shale and Tight Reservoirs

Although the flow back from the above oil-wet case was much more
than that from the water-wet case, the regained permeability could be either
more or less in the different stages of flow back. Fig. 12.39 shows that the
regained permeability to pentane in the initially water-wet core was lower
than that in the initially oil-wet core, but higher at late time. This is because
in the water-wet core, water imbibed deep into the core by capillary pres-
sure and the flow back of the imbibed water took some time; initially the
regained permeability was low; after more water was removed near the frac-
ture face, the permeability was significantly regained, resulting in higher
permeability than that in the oil-wet core, because generally the oil perme-
ability in an oil-wet core is depressed. For the case of oil-wet core with a
surfactant solution, the regained permeability followed the trend in the
oil-wet core without surfactant, but higher. From oil production point of
view, it seems that water-wetness is preferred from this example.
Tangirala and Sheng (2019b) compared the surfactant roles in the soak-
ing process and the invasion and flow back processes. The cores were initially
oil-wet and saturated with a crude oil. Amott type of experiments were con-
ducted to study the soaking process. Three tight cores (crab orchard labeled
T1, T2 and T3) of w11% porosity and three conventional cores (labeled

Figure 12.39 Comparison of changes of regained permeability to pentane under
various conditions (Liang et al., 2017d).