Introduction

Infill drilling (i.e., drilling of additional wells after initial primary and/or secondary development of a field) played an important role in improving waterflood recovery in West Texas in the 1970s. Infill drilling would essentially result in acceleration of production in an ideal homogeneous reservoir but no incremental recovery. However, additional recovery can be obtained in heterogeneous reservoir without reservoir continuity.

Figure 6-1 shows a plot of oil production rate vs. time for decline curve prior to infill drilling (base case), acceleration, and incremental recovery cases. In case of acceleration, the area under the acceleration curve is equal to the area under the decline curve. Also, the areas A and B between the acceleration and decline curves are equal. In case of incremental recovery, the area under the incremental recovery curve is greater than the area under the decline curve. Also, the area C between the incremental recovery and decline curves is greater than the area D between the incremental recovery and decline curves.

Figure 6-1: Production Rate vs. Time

Figure 6-2 shows a schematic of discontinuous layered reservoirs with injectors and producers. The layer connectivity and waterflood recovery potential are given in Table 6-1. Ideally speaking for optimum recovery, the injectors and producers need to penetrate all the oil bearing layers which require closer spacing.