Page 171 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Water injection 155

Figure 7.2 Well layout for one Bakken area in North Dakota (Hoffman and Evans, 2016).

well (Hoffman and Evans, 2016). The close offset well (about 880 feet away)
had a huge increase in water production, but the oil rate did not increase
during this time. The water broke after 1 week. Because of water break-
through at some stages, the injection well was finally closed. In early
2015, the closest offset well was shut-in for a couple of months. When it
was reopened, the oil rate increased. This test showed that one problem
for waterflooding is water breakthrough.

7.2.4 Waterflooding in Bakken Viewfield in Saskatchewan
This formation is a low-permeability formation. Experience or performance
from this formation may also be useful for developing shale and tight forma-
tions. Starting in 2006, waterflooding after 2e6 years of depletion by hor-
izontal injectors with multistage fracturing was launched. Line-drive patterns
were used. Before widespread waterflooding, several pilots were conducted.
Most of the horizontal injectors had 1600 m length. The well spacing from a
horizontal injector to a neighboring producer was about 200 m. Water
broke through right after waterflooding, but the oil rate peaked in the first
year, avoiding negative cash flow in early years. The oil decline rate was
decreased from 43% to 45% per year for depletion to 25%e38%. Horizontal