Methods To Obtain Quick Estimates of Formation Parameters in Interference Tests Derived From Features of the Line-Source Solution—Theory and Application

Abstract

Summary Interference testing is the oldest, but still the most effective, way of establishing communication between wells and determining the interwell-reservoir transmissibility. Yet these tests are not run frequently because often the results are difficult to analyze as a result of unforeseen complications. This paper presents practical methods derived from the properties of the line-source solution that is used to design and interpret effective interference tests. In single-well transient tests, early-time features of the exponential integral function occur too early to be observed. However, these features appear much later in an interference test and can be used in an observation well 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, and the pressure response itself exhibits an inflection point. With these characteristics, simple geometrical methods are proposed to estimate reservoir parameters. Moreover, a new expression of the “lag time,” or delay in the response, is formulated. The particular case of falloff or buildup is studied in detail, because the time lag in the reservoir response can bring extra information. A field example is included to demonstrate the application of these methods to actual data and their usefulness to a practicing well-test engineer.