Page 205 - Enhanced Oil Recovery in Shale and Tight Reservoirs

188 Enhanced Oil Recovery in Shale and Tight Reservoirs

Faulkner and Rutter (2000) also attributed the permeability reduction to
the water adsorption on mineral surfaces so that the pores became smaller;
the permeability reduction might not be caused by clay swelling. In other
words, nonswelling minerals could also have lower water permeability.
For this liquid adsorption mechanism to inhibit flow, the pores must be
very small, probably few nanometers. Zhang and Sheng (2017a, 2018)
also observed that the shale core permeability measured using water is several
times up to 100 times lower than that measured using nitrogen, after the
cores were hydrated. However, in their original paper, they attributed this
difference to clay swelling, which is not. It is caused by liquid adsorption
in small pores.
Roshan et al. (2015) measured the upstream pressure (with the down-
stream being atmospheric), when a fractured core (split into two halves)
was flooded. The core was under 1000 psi (6.9 MPa) confining pressure.
A 10 wt.% NaCl solution, followed by deionized (DI) water, was injected
into the core for approximately 4 h. Fig. 8.13 shows the upstream pressures
of the core when 10 wt.% NaCl solution and DI water were flooded. The
upstream pressure maintained almost constant in the case of 10 wt.% NaCl

Figure 8.13 Upstream pressure measurements versus time during the fracture perme-
ability test when (A) 10 wt.% NaCl solution was used, and (B) deionized water was used
(Roshan et al., 2015).