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5.2.2. Discussion
The elliptical patterns of water infiltration shown in Figure 7.9 demonstrate the
dominant impact of the CB pattern on the gross direction of fluid transport. In fact, the
saturation maps for the two cases are at first strikingly similar (Figure 7.9a), indicating
that the production wells exert a minor influence on transport when compared to
channeling of flow along the dominant band trend. These directional transport effects are
more pronounced than the relatively modest ∆P ratios presented in Figure 7.7 would
suggest.
The 56% increase in production efficiency gained in Case 2 for a 45° rotation of the
five-spot well configuration is a significant (but not optimized) result that could vary
substantially within the CB pattern and for different production configurations. In
addition, the scale of our five-spot, as constrained by the available mapped area, is
smaller than would typically be installed in a real reservoir production situation.
Nonetheless, the petroleum engineer can glean two valuable insights from our results—
that the presence of CB arrays can strongly affect production efficiency in reservoirs, but
also that relatively simple adjustments in well placement can be made to mitigate and/or
harness those effects.
5.3. Contaminant transport
In order to examine how the CB array would affect contaminant transport and
influence the evolution of a point-source plume, we established a fixed leak location for
each of three regional pressure gradient directions: parallel to the dominant band trend,
oblique (45°) to the trend, and normal to the trend (Figure 7.11). We considered
incompressible contaminant transport (mobility ratio = 1), and neglected physical
dispersion. A consistent regional gradient of 0.23 Pa/m (enough to yield an average flow
rate of approximately 7.7 m/year in the absence of CBs) was established in each of the
three directions by specifying pressures for an array of eight wells distributed around the
perimeter of the model domain (just inside the oval no-flow boundary). Each simulation
represents 30 years at a constant leak rate of 0.08 m 3 /day. For each scenario, a
corresponding CB-free control simulation was conducted. The results of all the
simulations are presented in Figures 7.12, 7.13 and 7.14.
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