Page 253 - Reservoir Formation Damage

Single-Phase Formation Damage by Fines Migration and Clay Swelling 233

pack decreased to zero. Because, in the fine sand pack, almost all the
pathways are of the plugging type. Whereas, in coarse sand packs, the
deposition tended to occur almost uniformly along the sand pack and the
mean permeability of the sand pack decreased to an equilibrium value.
Because, in the coarse sand pack, most of the pathways are of the
nonplugging types.
Gruesbeck and Collins (1982) state that their computer simulation
produced results similar to measurement reported in Figure 10-27. Civan
et al. (1989), and Ohen and Civan (1990, 1993) also simulated these
experiments successfully.

Consolidated Core Tests. Gruesbeck and Collins tested Berea and field
cores. First, the Berea cores were tested using

1. 2% KCl brine in a dry core (single phase system)
2. 2% KCl brine and white oil at a 50/50 ratio in a dry core (two phase
system)
3. white oil in a dry core (single phase system)
4. white oil in a core at connate 2% KCl brine saturation (two phase)

Cores were tested at various constant injection rates over a period of
time determined by a prescribed, cumulative pore volume amount of the
injection fluid. During each test, the pressure difference was measured
and the permeability was calculated using Darcy's law. Typical results
obtained using a 2% KCl brine in a Berea core are presented in Figure
10-28. As can be seen, the permeability remained unchanged at the low
3
flow rate of 0.0367cm /-?, while it decreased further at each of the
3
increased high flow rates of 0.0682, 0.1002, 0.1310, and 0.1702cm /s.
The final permeability values attained after each of the high flow rates
are used to calculate the permeability reductions from the initial state,
which are then plotted against these high flow rates as shown in Figure
10-29. The results shown in Figure 10-29 are indicative of surface
particle removal, similar to Figure 10-24. They stated that the removal
of indigeneous particles in the cores from the pore surface and subsequent
redeposition at the pore throats caused the permeability reduction.
Second, core samples were taken from an oil field, indicating an
abnormal decline of productivity in some wells. These cores were tested using

1. white oil in a dry core
2. white oil in a core at connate 2% KCl brine saturation.

The experimental results presented in Figure 10-30 indicate a trend
similar to Figure 10-29.