Paper: Application Of The Pressure Derivative With Acoustic Data

A pressure buildup on a pumping well may be conducted by either of two methods. Direct measurement, of course, involves placing a gauge downhole. This presents special problems, however, for a pumping well. Since this procedure involves pulling the rods and pump in order to get the gauge downhole, it is usually economically infeasible. In addition, this "pulling" process introduces a new transient into the formation which adversely affects the analysis unless the well is restabilized once the gauge is downhole. The second method involves acoustically determining the depth to the gas-liquid interface, measuring the casing pressure, and calculating the downhole pressure from these two measurements. With this method, an appropriate correlation must be selected in order to correct the liquid gradient for the gas in the column. The pressure derivative is an analysis tool which has received considerable attention lately. l-6 The two primary applications of the derivative are (1) identifying the different flow regimes and (2) obtaining a unique type curve match. Since the derivative involves a point-wise pressure difference rather than the pressure rise since the start of the test, it tends to amplify even small changes. For this reason, most examples have used data that was obtained from electronic pressure gauges. The purpose of this paper is to show that the pressure derivative may be applied to acoustic data. Two examples will be presented showing (1) a well with wellbore storage and skin and (2) a fractured well.