Page 402 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Fracturing fluid flow back 373

Figure 12.32 Effect of water handling cost on the NPVs for different shut-in times.

The early-time plateau represents the removal of trapped water and oil,
while the late-time plateau represents the single-phase oil flow. Several ob-
servations may be made. (1) The final regained k ro ’s in the desiccated cases
are higher than those in the nondesiccated cases, because less mobile water
is available in the former cases. (2) The final k ro ’s reach the same value at late
time because of complete removal of mobile water for the desiccated cases;
but for the nondesiccated cases, k ro s cannot reach the same value in realistic
time of flow back. (3) for both desiccated cases and nondesiccated cases, the
shut-in time decreases the regained k ro .
More generally, the processes of shut-in and flow back are divided into
the shut-in immediately after hydraulic fracturing or before the first flow
back (pre-flow-back shut-in), flow back, post-flow-back shut-in, and
extended flow back (production). Wijaya and Sheng (2019c) studied these
pre- and post-flow-back shut-ins. In the literature and earlier in this chapter,
the shut-in before the flow back is discussed. Here the shut-in past-flow-back
is discussed. The duration of the initial flowback is 10 h in a nondesiccated
model. Fig. 12.34 shows that the shut-in time is longer, the regained k ro
becomes lower, indicating the shut-in is not beneficial.