Page 32 - Enhanced Oil Recovery in Shale and Tight Reservoirs

22 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 2.13 Oil recovery factor vs. dimensionless time from the simulation models of
different scales.

oil and penetrate further into the reservoir, increasing gas contact with oil.
But too high pressure may push oil far away from the well. Laboratory results
show that intermediate velocity led to the best performance for conven-
tional reservoirs. In shale and tight reservoirs, a higher injection pressure
that corresponds to a higher velocity provides a better performance.
However, as the pressure is further increased, the incremental oil is reduced
so that the oil recovery factor is similar to that in a lower pressure, if huff-
n-puff injection is long enough (Song and Yang, 2013).
The effect of huff pressure is opposite to that of puff pressure. When the
puff pressure is lower, higher drawdown occurs. Then the recovery rate is
higher. Sheng and Chen’s (2014) and Sanchez-Rivera et al.’s (2015) simu-
lation results show that a larger drawdown leads to a higher oil recovery
factor; the benefit of larger drawdown is more important than maintaining
miscibility near the wellbore by raising the puff pressure.
In laboratory, if the core size was the same, the effect of pressure was
actually the effect of pressure depletion rate. In real reservoirs the pressure
is depleted at a different or slower rate than in a typical experiment in lab-
oratory. To make use of laboratory results for field performance prediction,
it is necessary to study the effect of pressure depletion rate.
Yu et al. (2016a) used two Eagle Ford outcrops (LEF_3 and LEF_4) to
study the effect of pressure depletion rate using the experimental apparatus