Page 33 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Huff-n-puff gas injection in oil reservoirs 23

(A)

(B)
Core LEF_4
20%

16%
Cumulative RF 12%

8%
PDT = 0.05 hr
PDT = 12 hr
4% PDT = 24 hr
PDT = 48 hr
0%
1 2 3 4 5 6 7 8
Number of cycles
Figure 2.14 Effect of pressure depletion rate, (A) LEF_3 and (B) LEF_4.

shown in Fig. 2.4. The cores had the porosity of 9.7% and the permeability
of 300e500 nD. Nitrogen and a Wolfcamp dead oil of 8 cP viscosity were
used. The soak time was 12 h (hours). The soaking pressure of 1000 psi was
depleted to the atmosphere within 0.05, 12, 24, and 48 h. The data in
Fig. 2.14 shows that as the pressure depletion rate was decreased, the oil re-
covery decreased. They also used a simulation model to history matched the
experimental data for the LEF-3 core, as shown in Fig. 2.15. More work was
done earlier (Yu and Sheng, 2015).