Page 403 - Enhanced Oil Recovery in Shale and Tight Reservoirs

374 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 12.33 Effects of shut-in before flow back and desiccation on regained k ro .

Wijaya and Sheng (2019c) also compared the shut-in performance of the
pre-flow-back with that of post-flow-back in a nondesiccated model as
shown in Fig. 12.35. It shows that the regained k ro for the shut-in post-
flow-back is higher than that pre-flow-back; the k ro without any shut-in
is the highest.
In tight gas formations, shutting in wells to allow closure can be very
detrimental to ultimate production due to proppant setting in non-cross-
linked fluids. Additionally, the supercharge from the treatment is lost.
The supercharge is the buildup of leaked fluid near the fracture or wellbore
so that the pressure is built up. The stored energy in the compressed min-
erals, liquids, and gases helps to recover substantial volumes of fluids, even
in underpressured reservoirs, if the flow back follows immediately after
the treatment. In medium- and high-permeability formations where
cross-linked fluids are routinely used and proppant concentrations within
the fracture are considerably higher, wells should be shut-in for enough
time to allow the fracturing fluid break, then flow back (Malone and Ely,
2007).