Page 397 - Enhanced Oil Recovery in Shale and Tight Reservoirs

368 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 12.26 Effect of SDP on cumulative oil production.

water in the HF moves to this location. Then S w decreases until 300 days
because of dissipation deep into the matrix. When the flow back starts at
300 days, S w increases again because the water dissipated earlier flows
back! At the location of 8 inches away from the HF, S w (red dotted line)
slightly decreases (<0.02) in the first 10 days because of dissipation, then
it increases again until about 150 days because the water closer to the HF
dissipates to this location. From 150 to 300 days, S w decreases because of
dissipation deep into the matrix. At 300 days, S w suddenly decreases for a
very short moment because of flow back; then it increases again because
the water deep in the matrix flows back. Contradictory to one’s belief,
the water saturations near the HF-matrix interface in the 300 days of
shut-in actually increase during some of 300 days.
Now look at the water saturations in the case of immediate flow back
(s0) (two solid curves). S w (solid blue) at 2 inches away from the HF keeps
increasing because the water leaked earlier flows back. Interestingly, the S w
at this location in the s0 case (solid blue) is lower than that (dotted blue) in
the s300 case from 0 to 110 days. The S w (solid red) at 8 inches away from
the HF decreases in the first 10 days and then increases again. However, the