Page 163 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Gas flooding compared with huff-n-puff gas injection 147

This project also demonstrated that the injected lean gas could vaporize
natural gas liquid (NGL) content. The original solution gas from the Bakken
formation in the pilot area had an NGL content (C 2 eC 7 ) of 225e250 bbl/
MMSCF. The injected gas had NGL of 138e145 bbl/MMSCF. One well
data showed that the NGL yield increased from 2.2 to 5.6 bbl/d. The oil
production from this well increased by about 10%.
There are several important learning points from this pilot test. (1) An
injector to producer well ratio of one to nine was a key factor in the eco-
nomic success of this project. This ratio was much lower than a typical
one to one ratio for waterflooding. This practice reduces surface infrastruc-
ture costs and increase production time. (2) Compared with water injection,
gas injection required less capital investment and gas was a nondamaging
injection fluid.

6.4.2 Gas flooding in Bakken formation in North Dakota
(Hoffman and Evans, 2016)
One waterflooding pilot was performed in the Bakken formation in the
North Dakota area in 2012e13. However, it was not successful. It was con-
verted to gas injection in 2014. The horizontal injector was surrounded by
four horizontal producers. Produced natural gas was used. Gas was reinjected
for 55 days in the middle of 2014 at a rate of 1.6 MMSCF/d and at the surface
injection pressure of 3500 psi. All the production from four producers
increased in the months immediately after the gas injection. Because the wells
further to the west producer were being hydraulically fractured,
the production increase at the south and west wells might be caused by the
fracture-hits. The other two wells (north and east) might not be hit by frac-
tures. After 1 week of gas injection, gas rate was increased to 160 MSCF/d at
the east offset well, or about 10% of the injected gas was being produced at
this well. The well was subsequently closed for 1 month. After the well
was reopened, the gas rate was high and the oil rate peaked for a short
time and then went back to the normal decline. The north offset well had
oil rate increased by three times, probably due to long-distance fracture-hit.
Gas flooding improved oil production in this case.

6.4.3 CO 2 injection in Song-Fang-Dun Field, Daqing (Jiang
et al., 2008)
ACO 2 flooding pilot was carried in the Fuyang Layer in the Fang-48 fault
block, Song-Fang-Dun Field, Daqing, China, starting in March 2003. The
porosity was 12%, and the air permeability was 0.79 mD. The oil viscosity