Average pressure and permeability values from formation and well tests apply within the area or volume investigated. To integrate these measurements with each other and with other measurements sensitive to permeability and reservoir heterogeneity, it is essential to understand where these values are meaningful. From the practical point of view, the pressure gauge sensitivity is also a consideration.

The conventional approach for a well test is computation of the test radius of investigation. This technique has no application for tests that terminate in a nonradial geometry. Field data that have been published illustrate tests that have terminated in spherical flow (partially completed well), linear or bilinear flow (hydraulically fractured or horizontal well), pseudoradial flow (hydraulically fractured or horizontal well, well near a linear boundary), linear flow (well in elongated reservoir), and pseudosteady state flow. The test radius of investigation concept is equally unworkable for formation tests.

Simple formulas extend the concept of test radius of investigation to nonradial flow geometries. This approach permits meaningful integration of transient test interpretation results (permeability and average pressure estimates, and characterization of inner and outer boundary geometries) in reservoir characterization and in well productivity evaluation.

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