The fluid flow in porous media has been addressed in literature for obvious reasons. A large portion of petroleum engineering literature was focused on developing solutions for different flow/well models. Composite reservoir model has drawn attention of well testing researchers. The complexity of oil reservoirs in the field make the use of developed models limited. A composite reservoir is made up of two or more regions. Each region has its own rock and fluid properties. A composite system can occur naturally or may be artificially created. Aquifers with two different permeabilities forming two regions, oil and water regions or gas and oil regions with different properties in a reservoir are examples of naturally occurring two-region composite systems. For a well in a radial composite reservoir, the reservoir model usually considered is the radial composite model, in which the well is centered in a circular region of mobility M1 and storativity S1. Beyond this inner zone, the reservoir has mobility M2 and storativity S2. The outer zone mobility may be either higher or lower than that of the inner zone. Field engineers are inclined to use oil flow models for interpreting well tests as long as these wells produce dry. The fluid fractional flow in formation, however, changes as more water encroaches toward the producing well.

This paper presents a study focusing on an important application of the use of analytical solutions of composite reservoir model to evaluate the impact of non-unit mobility flow. This is of paramount importance in fields with big differential of mobilities of oil and water as in this study. This research work is to highlight the significance of consideration of water flow impact in formation before wells start cutting water. The solutions were validated with other semi analytical solution and supported by field data.

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