This paper presents a new method of pressure transient analysis for determining the vertical and horizontal permeabilities from a single-well test conducted on partially penetrated or perforated wells. Generally, well testing data from wells with a restricted flow entry potentially carry the information about directional permeability. It has been recognized that the test data can be characterized by two parameters: the ratio of the flow entry to the total thickness of the producing zone, and the ratio of the vertical permeability to the horizontal permeability. Fully-featured pressure drawdown data display two straight-line segments connected by a transition curve when plotted versus the logarithm of time. This paper defines a characteristic time that corresponds to the intersection point of the extrapolations of the two straight lines, and shows that the characteristic time is a function of the penetration ratio and the permeability ratio. By using the slopes of the two straight lines and the characteristic time, one can determine the vertical and horizontal permeabilities, and the net thickness of the producing zone. This paper demonstrates that the slope of the second straight line can be obtained from pressure buildup data. Hence, a full development of the pressure drawdown process is not necessary and the total testing time can be reduced. Also, by applying the real gas pseudo pressure concept, the proposed method can be extended to single-phase, highly compressible fluid flow in reservoir under Darcy's flow conditions. Examples show the test data interpretation procedure for liquid and gas flow problems.

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