Vertical permeability magnitude is critical to well trajectory and/or completion design whenever the oil is either overlain by a gas cap or underlain by an aquifer or whenever a slanted or horizontal well is planned. Various authors have provided ways to determine horizontal and vertical permeability from a pressure transient test in a well with a limited entry completion. However, none indicate a test design that will ensure that the vertical permeability can be determined.

This paper provides the necessary test design considerations for horizontal and vertical permeability determination from a conventional pressure buildup test. A standard limited entry model for the pressure transient behavior is used to determine timing for the start and end of key flow regimes for the transient interpretation. Equations that can be used to design a test for vertical permeability determination are also used to indicate ranges of reservoir, fluid and well properties that result in a successful test.

A quick look analysis procedure enables estimation of horizontal and vertical permeability directly from a log-log diagnostic plot of pressure change and its logarithmic derivative. Examples illustrate test design and interpretation applications and demonstrate that determination of vertical permeability is possible even when wellbore storage masks early radial flow and an overlying gas cap and/or underlying aquifer prevent the appearance of late radial flow.

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