Page 210 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Fluid-rock interactions 193

hard rock if >30 GPa. Under the same conditions (300 F for 48 h), the
Young’s modulus of a middle Bakken core reduced by 52.39% and
51.97% when exposed to 2% KCl water and fresh water, respectively; the
Young’s modulus of a Bakken core reduced by 32.88% and 40.61% when
exposed to 2% KCl water and fresh water, respectively. When the Young’s
modulus was reduced, the fracture conductivity was decreased (see
Fig. 8.19). Morsy et al. (2013a) reported 5% NaCl and HCl solutions also
weakened Eagle Ford shale samples.
Abousleiman et al. (2010) found that Middle Woodford shale was weak-
ened when exposed to the oil-based mud with low-salinity (50,000 ppm
CaCl 2 ). But the ultimate strength of the shale increased when exposed to
the high salinity oil-based mud, indicating that shale strengthening by
appropriate fluid chemistry is possible. Interestingly, their experimental
data even showed that shale strength was increased with longer exposure
time to two water-based mud. Generally, water would weaken the shale
strength. Younane Abousleiman (personal communication on February
20, 2019) explained that those fluids were emulsified (different additives
added to water-based muds and intended to minimize water-shale invasion
effects). Apparently, those mixes increased shale strength. However, detailed
additives were not unknown.

Figure 8.19 Fracture conductivity reduction corresponding to Young’s modulus reduc-

tion for different shale cores exposed to 2% KCl slick water at 300 F for 48 h. Data from
Akrad, O.M., Miskimins, J.L., Prasad, M., 2011. The effects of fracturing fluids on shale rock
mechanical properties and Proppant Embedment. Paper SPE 146658 Presented at the SPE
Annual Technical Conference and Exhibition, Denver, Colorado, USA, 30 October-2
November. doi:10.2118/146658-MS.