Flow rates occurring during production and interference tests are seldom constant. This paper presents an analytical method of solving for pressure as a function of time for variable flow rates. The cases examined are for linear, exponential and harmonic production declines.

The analysis of a variable flow rate can provide more information than the analysis of a constant rate. The procedure is simple and does not require the the application of superposition. To force a well to produce at a constant rate or to assume that it produced in a step like manner may complicate the arithmetic, induce errors and often restrict the number of parameters that can be solved.

The variable rate technique is particularly useful where the flow rate is continuously monitored. A common case is a drill stem test where the production can be determined accurately as the fluid level rises in the string and the rate is continuously changing with time. In the case where a well dies during a test this technique has proved very useful.

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