Page 27 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Huff-n-puff gas injection in oil reservoirs 17

The whole process lasts about 1 hour. And the experiment lasts 24 h or more
hours for some experiments. The oil recovery factor is calculated from the
collected fluid compositions by GC.

2.3.3 Experimental verification of huff-n-puff effectiveness

The simulation work from Wan et al. (2013a) and Chen et al. (2013)
demonstrated the EOR potential of huff-n-puff gas injection in shale cores
and shale reservoirs. The potential needs to be verified by experiments, as
initial concerns were: (1) during the huff (injection) period, insignificant
amount of oil could come out of the core by countercurrent flow of oil
and gas, as the injected gas pressure was high and the gas was injected
from all the core surfaces; (2) during the puff (production) period, because
the oil compressibility was low, limited gas could enter the core, and thus
the resultant pressure energy was limited that drove oil out of the core;
(3) as a result of those two reasons, the huff-n-puff process might lead to
a cycle of injecting and producing gas.
To verify the EOR potential, an experimental setup similar to that pre-
sented in Fig. 2.4 was first used by Gamadi et al. (2013). Outcrop core plugs
(unfractured matrix cores) from Eagle Ford, Barnett, and Marcos shales were
used. Soltrol 130 mineral oil and nitrogen were used. The effects of soak
time, injection pressure, and other parameters were investigated. The results
showed that huff-n-puff gas injection could increase a significant oil, as
shown in Fig. 2.9 as an example.

Figure 2.9 Huff-n-puff nitrogen injection performance from Mancos, Barnet, and Eagle
Ford cores.