Page 207 - Enhanced Oil Recovery in Shale and Tight Reservoirs

190 Enhanced Oil Recovery in Shale and Tight Reservoirs

increased. However, particle detachment may clog the pores depending on
the mass of solids being mobilized and the fracture network structure.
By the way, Fig. 8.15 shows the axial displacements of the core measured
by LVDT when flooded by the 10 wt.% NaCl solution and DI water,
respectively. The sample shrank slightly when exposed to the NaCl solution
(Fig. 8.15A), while relatively larger axial swelling of 0.03% is observed in the
test with DI water (Fig. 8.15B).
Improvements to microfracture generation from water-shale interactions
could lead to improved rates and recoveries. However, Kurtoglue (2013)
reported that for all the Bailey shale cores, a higher oil volume was displaced
than the water imbibed in the core. The water used was fracturing fluid and
2% KCl water. That means the swelling reduced pore volume; the pores
became smaller; and the permeability became lower. In other words,
swelling reduced core permeability. She also reported that the average oil
recovery was 50%e60% from high permeability laminated clay-rich samples
(samples 1e3), and 23% from low permeability calcite-rich sample (sample
4). Those samples were more oil-wet, but water imbibition took place

Figure 8.15 Axial displacement measurements show (A) slight shrinkage (positive
displacement) of the shale core when a 10 wt.% NaCl solution was flooded, and
(B) swelling (negative displacement) when deionized water was flooded (Roshan
et al., 2015).