structural geology, propagation mechanics and - Stanford School of ...

5.2. Reservoir production
A standard five-spot production-well configuration—square, with central injector and
producers at the corners—was used to simulate two-phase (oil-water) incompressible
flow within the band pattern. Two case scenarios were modeled using the same 5.5-acre
pattern (150 m on a side)—the only difference being a 45° rotation of the production-
wells about a fixed injector location (Figure 7.8). In Case 1, the straight-line path from
injector to two of the producers runs generally along the dominant band trend, while the
path to the two other producers runs generally across it. In Case 2, the straight-line paths
from injector to all four producers run oblique to the dominant band trend. For both cases,
we specified complete initial saturation of the pore volume with oil, exact balance at all
times between the total volume of water injected and the total volume of fluid produced,
and equal pressure at all four production wells. A total injection/pumping rate of 15.9
m 3 /day was used and both simulations were run for 250 days, yielding a total pore volume
injected (PVI) of 0.15 (i.e. 15% of the total model pore volume). Relative permeability
was accounted for using representative data for light crude oil (viscosity 2 cp) as the
nonwetting phase and formation water (viscosity 1 cp) as the wetting phase in granular
media similar to the Aztec sandstone (Table 1). Capillary pressure is neglected in these
simulations, as attempting to include it produced computational problems. The efficient
handling of strong capillary effects may require the modification of some of our
numerical treatments. The simulation results are presented in Figures 7.9 and 7.10.
5.2.1. Results
Figure 7.9 shows equivalent saturation-map snapshots for the two simulations at
approximately 0.03, 0.09 and 0.15 PVI. In both cases, the elliptical patterns of water
infiltration that develop suggest a strong tendency toward preferred transport along the
dominant band trend. Judging from the aspect ratios of the infiltration patterns, the
transport rate along the band trend exceeds that across it by at least a factor of two. This
effect results in early breakthrough of water to the production wells oriented along the
band trend from the injector in Case 1 at < 0.03 PVI (Figure 7.9a). For Case 2, significant
breakthrough does not occur until 0.09 PVI (Figure 7.9b). These diverging results are
clearly reflected at 0.15 PVI (Figure 7.9c), when the substantially greater area of water
infiltration for Case 2 illustrates that 56% more oil has been produced than in Case 1.
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