Page 170 - Enhanced Oil Recovery in Shale and Tight Reservoirs

154 Enhanced Oil Recovery in Shale and Tight Reservoirs

5.1%. The porosity in the pattern area was from 14% to 18% and the perme-
ability was less than 1 mD (Thomas et al., 2014).

7.2.2 Waterflooding in Bakken formation in North Dakota
Meridian Oil injected water in NDIC 9660 in the Bicentennial Field in
McKenzie County early in 1994. Approximately 13,200 barrels of fresh-
water were injected into a horizontal well in the Upper Bakken Shale in
50 days. The well was shut-in for 2 months. After that oil production
remained below the rates before water injection for the rest of the well’s
operational life (Sorensen and Hamling, 2016).
One waterflooding pilot was performed in the Bakken formation in the
North Dakota part. One horizontal injector was surrounded by four hori-
zontal producers (Fig. 7.1). The east and west offset wells were 2300 ft
away and the north and south offset wells were 900 and 1200 ft away
from the injector. The injection rate was about 1350 bbl/day for 8 months
in the middle of 2012. The bottom hole pressure at the injector increased to
about 6000 psi, and the east and west producers’ water rates increased. How-
ever, no incremental oil was observed. The injection was stopped for about
6 months at the end of 2012 and begun in 2013 again and continued for
8 months. During the second period of water injection, the injection rate
was decreased, and the bottom hole pressure was maintained at 5500 psi.
Again, no incremental oil was seen. About 444,000 STB of water was
injected, but only 65,000 STB of additional water was produced. Later wa-
ter injection was converted to gas injection (Hoffman and Evans, 2016). The
gas injection performance is reviewed in the Gas Flooding section. The
failure of this waterflooding pilot seemed to be caused by low water sweep
efficiency, because much less water was produced than the water injected
(water lost). Therefore, this case may not be used to generalize waterflood-
ing performance in shale or tight formations. Another comment is about the
well layout as shown in Fig. 7.2. The horizontal well pattern is similar to the
inverted five-spot pattern for vertical wells. Whether such a pattern can have
a good sweep efficiency and effectively displace oil to producers is the
question.

7.2.3 Waterflooding in Bakken formation in Montana
The test was conducted in 2014. There was one injection well and several
offset wells. In the first 3 months, the well injection rate was 1700 STB/
d, and later reduced to 1000 STB/d because of breakthrough at a close offset