Page 75 - Principles of Applied Reservoir Simulation 2E

60 Principles of Applied Reservoir Simulation

The ratio of the number of producing wells to the number of injection wells is
shown in Table 7-1. The patterns depicted in Table 7-1 and Figure 7-1 are
symmetric patterns that are especially effective for reservoirs with relatively
small dip and large areal extent. The injectors and producers are generally
interspersed. Other patterns in which injectors and producers are grouped
together may be needed for reservoirs with significant dip. For example, a
peripheral or flank injection pattern may be needed to effectively flood an
anticlinal or monoclinal reservoir.

Table 7-1
Producer-to-Injector Ratios for Common Well Patterns
Well Pattern Producer : Injector Ratio
Four-Spot 2

Five-Spot 1
Direct Line-drive 1

Staggered Line-drive 1
Seven-Spot 1/2
Nine- Spot 1/3

The location of injection wells depends on factors such as reservoir
structure, injected fluid type, and displacement mechanism. For example,
upstructure gas injection can be an effective displacement process for producing
a monoclinal reservoir containing oil. It relies on the movement of a gas-oil
contact and the displacement of oil to downstrucrure production wells. On the
other hand, downstructure peripheral injection of water can be used to displace
oil to upstructure producers in an anticlinal reservoir. In this case, downstructure
water injection is used to move the oil-water contact upstructure and displace
oil to upstructure production wells. The same displacement concept applies to
production of an anticlinal oil reservoir with strong aquifer support.
In addition to reservoir geometry and displacement process, the well
pattern depends on the distribution of existing production wells and the desired
spacing of wells. Well spacing is an estimate of the area being drained by a