Page 178 - gas transport in porous media

Persoff
172
Figure 9.2 through Figure 9.4. The use of transparent replicas allowed visualization
which showed that this was due to intermittent blockage of gas flow paths at pore
throats.
Capillary theory suggests that for gas-liquid flow in a fracture, the larger pore
spaces will be occupied by gas (the nonwetting phase), and the smaller ones by
liquid; as long as the boundary pressures do not change, the pore occupancy should
be static. During two-phase flow in liquid-dominated conditions, pore occupancy
was indeed generally static in almost the entire fracture, but frequently certain critical
pores switched between gas and liquid occupancy, especially in liquid-dominated
conditions. In a typical liquid-dominated flow condition, one or more distinct gas
flow paths were evident. Part of the gas flow path was always occupied by gas, but
several stretches of the gas flow path were intermittently occupied by liquid. This

27
26 180
25
Inlet 170
24 160
Pressure (psia) 22 Gas 150 Pressure (kPa)
23
Liquid
21
140
20
Outlet
19 130
18
120
17
506.51 506.54 506.57 506.6 506.63 506.56
Time (hours after start of experiment)
Figure 9.2. Example of “throat-clearing” event that recurred approximately every 20 minutes. (8.5 µm
hydraulic aperture, Stripa replica, Expt A, gas:liquid volume flow ratio was 9.5)

18
120
Pressure (psia) 16 Liquid outlet Gas inlet 110 Pressure (kPa)
17
Gas outlet
Liquid inlet
15
100
14
530 532 534 536 538 590.7 590.9 591.1
Time (hr) Time (hr)
Figure 9.3. Examples of repeated blocking and unblocking events, alternating with periods of steady
flow (21.7 µm hydraulic aperture, Stripa rock, Expt C. gas:liquid mass flow ratio was 0.025)