Use of simultaneous flow-rate and pressure measurements to replace isochronal gas well tests

The interpretation of gas well pressure-transient tests differs from that of oilwell tests in two important respects: the nonlinearity of the governing equations and the presence of a rate-dependent (non-Darcy) skin. The nonlinearities are commonly avoided by use of pseudofunctions, and the non-Darcy skin effect is handled by use of flow-after-flow, isochronal, or modified isochronal tests. Recent investigations have shown that the simultaneous measurement of well flow rate with well pressure can significantly shorten the test duration required for accurate interpretation. These methods rely on use of the straight-line approach, however, and in some cases on trial and error. This paper describes a computer-automated interpretation approach that can be applied generally for any type curve without trial and error. The use of this interpretation technique can reduce the test duration to only that required for a standard drawdown or buildup test, and will allow the estimation of the stabilized deliverability potential without flowing the well until stabilization is reached. Examples of use of the method on both simulated and real data demonstrate its effectiveness.