Page 132 - Enhanced Oil Recovery in Shale and Tight Reservoirs

118 Enhanced Oil Recovery in Shale and Tight Reservoirs

are caused by the low injection pressure of 4000 psi. The initial reservoir
pressure is 6840 psi. Generally, we try to use a high injection pressure to
make the huff-n-puff more effective. This example shows that huff-n-puff
optimization is so important that without optimization, a wrong conclusion
about the effectiveness may be made. This chapter discusses the optimization
of huff-n-puff gas injection in shale oil reservoirs. Huff time, puff time, and
soaking time are investigated using simulation approach combined with
some laboratory results.

5.2 Setup of a base simulation model
Middle Bakken data were used to build a validated base model. The
compositional simulator GEM developed by Computer Modeling Group
(2014) is used. A horizontal well is fractured with 15 fractures. The model
has a half-fracture connected through a vertical well block (1,16,1). Then
the production data from this model represents the 30th of a horizontal
well production.
The schematic of the simulation model is shown in Fig. 5.1. Its dimen-
sions are 296.25 ft 4724 ft 5 ft. The stimulated reservoir volume (SRV)
has the fracture length of 724 ft in the J direction, the half-fracture spacing of
296.25 ft in the I direction, and 50 ft (formation thickness) in the K direc-
tion. The half-hydraulic fracture width is 0.5 ft. The detailed block sizes
of this base model are below.
The block sizes in feet in the I direction from I ¼ 1toI ¼ 11 are:

0.5 0.257312051 0.522150017 1.059571985 2.150134547 4.363156667 8.85392783
17.96681715 36.45913142 73.98462696 150.1331714

The block sizes in feet in the J direction of total 31 blocks are:

5*200 187.1636568 90.39505341 43.65839939 21.08584226 10.18389932 4.918551703
2.375529264 1.147317264 0.554123632 0.267626932 0.5 0.267626932
0.554123632 1.147317264 2.375529264 4.918551703 10.18389932 21.08584226
43.65839939 90.39505341 187.1636568 5*200

One block is used in the K direction with its size 50 feet.
Table 5.1 summarizes the matrix and fracture property data in the
non-SRV and SRV regions in the Middle Bakken shale (Kurtoglu, 2013).