A technique for analyzing interference test data is presented that employsthe time rate of pressure change - the pD' function. Thisfunction exhibits a maximum value of 0.736 at atD/rD2 of 0.25 for an idealline-source well. Several field examples are included to demonstrate theapplication of this technique in determining transmissibility (kh/µ) andstorage (fch) between a well pair. Introduction It has been pointed out that interference tests1 may be run withgreater ease and may take less time than pulse tests2,3 to developin-situ reservoir properties such as transmissibility (kh/µ) and storage(fch). An interference test consists of recording the transient pressureresponse at an observation well caused by a constant rate change at some sourcewell. The pressure response can help determine formation continuity, fracturesorientation, and areal average transmissibility and storage between a wellpair. Interference pressure data can be analyzed by (1) least-squares regressionanalysis coupled with a two-dimensional single-phase compressible-fluidreservoir simulator4,5 and (2) type curve matching6,7techniques. A rapid hand analysis method1 requires the recognitionof the maximum slope line on pressure response ?p vs. time curve plottedon a rectangular coordinate paper. This slope is used to determine thetransmissibility (kh/µ). The intercept of this line on the time scale isused to obtain storage (fch) between the well pair. The slope of the line gives the maximum value of the time rate of change ofpressure at the observation well. This maximum slope occurs at the inflectionpoint of the ?p vs. time curve. The time to reach this maximum slope ofinflection point is also a characteristic of the system and, therefore, can beused to determine the storage (fch) between the well pair. The examplespresented in this paper will illustrate this technique. In view of the above, it is necessary to develop the behavior ofpD' at an observation well due to a constant-rate source wellfor a proper understanding of interference test behavior. The wellbore storageeffects are assumed to be negligible at this source or active well. This ispresented in the next section in terms of dimensionless quantities forsimplicity. In later discussion, equations in oilfield units are used. It is emphasized here that the pD' function has been usedbefore in petroleum literature for water influx8–10 and wellborestorage11,12 calculations. Further, pD' behaviorhas been employed in detection of reservoir boundaries.13–15 Theseapplications will not be discussed in this report.
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Tiab et al. (1980) studied this question.