Interference testing is the oldest, but still the most effective, way of establishing communication between wells and determining the interwell reservoir transmissibility. However, these tests are not frequently run because the results are commonly difficult to analyze due to unforeseen complications.

This paper presents several practical methods to design and interpret effective interference tests based on the properties of the line-source solution. In single-well transient tests, early-time features of the exponential integral function occur at times that are too early to be observed. However, the distinctive pressure transient derivative features appear at an observation well much later during an interference test, and can be used to estimate the storativity and transmissibility ratios of the reservoir. The pressure response and the log-derivative of the pressure intersect on the log-log diagnostic plot for the observation well and the pressure response itself exhibits an inflection point. Based on these characteristics, simple geometrical methods are proposed to estimate reservoir parameters. Moreover, we formulate a new expression for the "travel time", or delay in the response. The particular case of fall-off or buildup is studied in detail, as the time lag in reservoir response can bring extra information. A field example is included to demonstrate the application of these methods in a field case and their usefulness to a practicing well test engineer.

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