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Single-point tests for gas wells
A single-point test for gas well deliverability is an attempt to overcome the limitation of long test times required for flow-after-flow tests. This article discusses the implementation and analysis of single-point testing for gas-well deliverability tests. Both the Rawlins and Schellhardt and Houpeurt analysis techniques are presented in terms of pseudopressures.
Single-point test procedure and analysis
A single-point test is conducted by flowing the well at a single rate until the sandface pressure is stabilized. One limitation of this test is that it requires prior knowledge of the well’s deliverability behavior, either from previous well tests or possibly from correlations with other wells producing in the same field under similar conditions. Ensure that the well has flowed long enough to be out of wellbore storage and in the boundary-dominated or stabilized flow regime. Similarly, for hydraulically fractured wells, the well must be flowed long enough to be in the pseudoradial flow regime and then stabilized.
To analyze a single-point test with the Rawlins-Schellhardt method, n must be known or estimated. An estimate of n can be obtained either from a previous deliverability test on the well or from correlations with similar wells producing from the same formation under similar conditions. The calculation procedure is similar to that presented for flow-after-flow tests. The absolute open flow (AOF) can be estimated graphically by drawing a straight line through the single flow point with a slope of 1/n and extrapolating it to the flow rate at . The AOF can also be calculated with
where C is estimated with
To use the Houpeurt analysis technique, the slope, b, of the line on a plot of
must be known. If a value of b is unavailable, estimate b using Eq. 1. Note that estimates of the formation properties are necessary to use Eq. 1. The remaining analysis procedure is similar to that for flow-after-flow tests.
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