Page 371 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Fracturing fluid flow back 343

into the large fractures by countercurrent flow. During the flow back, the
water will be trapped as the small fractures are closed, resulting in low water
and high gas production. In the simple fracture system, there are less contact
surfaces by water. Thus, less countercurrent flow between water and gas.
During the flow back, water can more quickly flow out, the small fractures
are closed, resulting in higher water rate, more gas trapped in the matrix
and low gas production.
Tangirala and Sheng (2019a) investigated the flow back and oil produc-
tion in hydraulically fractured water-wet formations using the Lab-on-
a-Chip method. A borosilicate glass chip was etched by the process of
chemical vapor deposition to form a uniform channel porous medium
network (20 10 mm footprint). The size of the chip was 45 15 mm.
The chip was manufactured by Micronit Microtechnologies B.V.,
Netherlands. The width and height of each channel were 50 and 20 mm,
respectively. The porosity of the channel network was 0.6 with two end
nodes, End A and End B (Fig. 12.3). A wide pore channel connected to
the inlet distributed the injected fluid evenly to the pore network. This
portion of the chip represented a fracture.
The chip was housed in a fluidic connect PRO chip holder which was
fixed over the mechanical stage of a fluorescence-imaging inverted micro-
scope (Olympus CKX-53). As shown in Fig. 12.4, fluids were pumped
by an air compressor whose pressure was controlled by the pressure regu-
lator, a pressure-based flow controller, MFCS-EZ, purchased from Fluigent
Inc. The flow rate was measured using the Flow Rate Platform (FRP) also
acquired from Fluigent Inc. and having a measurable range of 0e7 mL/min.
Before passing through the chip, the fluids were filtered through a 2 mm
inline polyether ether ketone (PEEK) filter provided by IDEX corporation.

Figure 12.3 A microchip with uniform porous network.