Page 497 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Other enhanced oil recovery methods 461

core wettability. A blend of wettability-altering surfactant (AOS and zwit-
terionic surfactant) not only altered the wettability from oil-wet to water-
wet, but also significantly increased the foam resistance factor in the presence
of oil.
An air foam test was started to improve injection profile before water
injection in An 83 zone in the Chang 7 formation in April 2013. In the
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350 m 150 m well pattern (An 231e45 well pattern), 7824 m of air
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was injected to generate 3631 m foam. The well production capacity was
increased from 0.55 to 0.88 tons/day on the average, a significant increase
compared with the capacity of 0.39 tons/day for the neighboring wells. Wa-
ter injection began in December 2013. The water cut in the corresponding
production wells started to increase. This test showed that air foam mitigated
water breakthrough (Wang et al., 2015).

14.5 Branched fractures

Branched fractures are generated by adding fiber in the fracturing fluid
whose viscosity is reduced gradually. After the main fracture is generated,
added fibers (0.1e0.3 wt.%) form a temporary bridge blockage with sand
within the fracture. The pressure is increased, and then the fracturing fluid di-
verts to understimulated intervals along the lateral to form branched fractures
(Potapenko et al., 2009). After the fractures are generated, the fluid viscosity is
gradually reduced. Thus, the fracture conductivity is achieved (Wang et al.,
2013). Branched fractures can be more easily generated when the difference
between the maximum and minimum horizontal stresses is small.
Fan and Liu (2016) reported a field case to generate branched fractures by
a large-scale fracturing operation in the Hailaer field, Inner Mongolia,
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China. For such a fracturing operation, 1631 m of fracturing fluid
3
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and 161 m sand per well on average were injected. About 7.8 m /d of
sand was injected per well. For this field, the average porosity was 15.3%,
and the permeability was 0.34 mD under an overburden confining condi-
tion. After fracturing, the average oil rate was increased by 5.7 tons/day
from 0.7 tons/day. After 500 days of fracturing, the average incremental
oil per well was 2244 tons. Totally six wells were tested.
Li (2012) reported the oil production performance (oil rate) using
different fracturing methods. The oil rates showed that the multistage
fracturing method and using polyhydric alcohol fracturing fluid worked
better.