Page 401 - Enhanced Oil Recovery in Shale and Tight Reservoirs

372 Enhanced Oil Recovery in Shale and Tight Reservoirs

the NPV increases in the 30-day and 60-day shut-in times over that in the 0-
day shut-in are negligible. When the permeability is 300 nD (base model)
and 1800 nD, the NPV for the immediate flow back is the highest.
Wijaya and Sheng (2019b) also checked the performance (NPV) of im-
mediate flow back at different oil prices and different water handling costs.
Figs. 12.31 and 12.32 show that with the ranges of different prices and costs,
the immediate flow back ranks the best.
Earlier, Wijaya and Sheng (2019a) studied the effect of desiccation on
shut-in benefits in removing water blockage. Desiccation refers to a state
in which the rock’s initial water saturation is below the irreducible water
saturation, often called subirreducible water. They built simulation models
to match Liang et al.’s (2017c) experiments in which a core was initially satu-
rated with oil, then water flooded presenting an invasion process; after some
time, the flooding direction was reversed with oil (n-pentane) flooding at a
constant flow rate to reach steady state flow; during the oil flooding,
regained oil relative permeability k ro was calculated using Darcy’s equation
assuming a single-phase flow although it was a multiphase flow.
Fig. 12.33 shows the effects of desiccation and shut-in before flow back.

Figure 12.31 Effect of oil price on the NPVs for different shut-in times.