Page 162 - Enhanced Oil Recovery in Shale and Tight Reservoirs

146 Enhanced Oil Recovery in Shale and Tight Reservoirs

Heels

Producers

Toes

Toes Injector toe
Injector heel
Producers

Heels

Figure 6.11 Viewfield gas injection pattern. Modified based on Schmidt, M., Sekar, B.K.,
2014. Innovative Unconventional2 EOR-A light EOR an unconventional Tertiary recovery
approach to an unconventional Bakken reservoir in Southeast Saskatchewan. Paper WPC-
21-1921 Presented at the 21st World Petroleum Congress Held in Moscow, Russia, 15e19
June.

the same. When gas broke through at the toe end of a producer, the toe
portion was plugged to alleviate gas cycling. The injected gas continued
moving to the next portion. This pattern enabled one injector to serve
the nine producers. For the producers with heels close to the injector, a
straddle packer system called “scab-liner” technique was applied at the
immediate heel port. Two packers were set, one in the upstream and the
other in the downstream of the problem fracture port, with the tubing in
between to allow flow through while still isolating port(s). This technique
proved to work in the pilot. The porosity and permeability of the Bakken
formation in the test area were 9%e10% and 0.01e0.1 mD, respectively.
The median pore throat size was 0.1e0.2 microns. The oil viscosity was
2e3 cP. The initial water saturation was 55%e59%. The initial pressure
was 2320 psi and the bubble point was 990 psi.
The project was initiated in December 2011. Initially, the injection rate
was 300 MSCF/d at the injection pressure of 500 psi. When compression
was added in March 2012, the injection rate was increased to 1 MMSCF/
d at 1000 psi. Immediately, gas broke through two pattern wells. The oil
production rate decreased to 53 bbl/d by July 2012. After workovers, oil
rates consistently increased in all of nine producers and the total rate climbed
to 295 bbl/d. The average decline rate of the pattern wells decreased from
20% before gas injection to 15% after gas injection. The project clearly
demonstrated that alleviation of gas breakthrough made the gas flooding
work. The gas utilization factor was 6.5e10 MSCF/bbl of oil.