Page 39 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Huff-n-puff gas injection in oil reservoirs 29

huff-and-puff field tests experienced soak periods ranging from 18 to
52 days, and the process performance appeared to be less sensitive to the
soak duration. In few CO 2 huff-n-puff projects in shale reservoirs, soaking
time was tens of days (Sheng, 2017a). From the experience of the author of
this work, simulation models show zero-soaking time is preferred in terms of
oil recovery.

2.7 EOR performance with number of cycles

Artun et al. (2011) did a parametric simulation study of a naturally
fractured reservoir (a conventional reservoir). They found the optimum
number of cycles was two to three based on net present value. However,
00
Fig. 2.21 shows the pictures of a core of 2 in diameter and 2 in length
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from the first cycle to eighth cycle of huff-n-puff methane injection (Li
and Sheng, 2016). The methane was injected at 2000 psi, the core was
soaked for 1 day and then the pressure was released to the atmospheric pres-
sure. The incremental recovery factors in each cycle for 10 cores are pre-
sented in Table 2.1. The figure and the table show that oil coming out
from the core decreased with the cycle. This is because it was easier for

Figure 2.21 A core with released oil during 8 cycles of huff-n-puff injection.