An operator successfully tested an offshore, exploration well in a high-pressure and a high-temperature (HPHT) reservoir, where the pressure exceeds 10, 000 psi and the temperature is approximately 400°F. The tested intervals are behind a 4.5-inch liner. Slimhole drillstem test (DST) tools have been considered but not selected due to the restricted internal diameter and limited intervention capability. Instead, a cased hole DST method has been selected in which DST tools are set in a 7-inch liner, and tubing-conveyed perforating (TCP) guns are run in the 4.5-inch liner on the bottom of a long tailpipe.

The first DST has been successfully completed, with the pressure gauges located at the gauge carriers in the 7-inch liner, several thousand feet above the test interval. Pressure and temperature data from downhole gauges have been analyzed and found to exhibit significant wellbore-phase redistribution effects because of gauge location. This has resulted in significant uncertainty in reservoir characterization. Solutions considering the HPHT and slimhole design have been investigated.

We present a unique method of placing the downhole gauges on top of the perforating gun during an HPHT well test operations where formation temperature exceeded 400°F. Five DSTs have been performed using this technique with successful recording of downhole pressure and temperature data, despite the perforating gun shock and hostile environment encountered.

A comparison of pressure transient interpretations as well as a comparison of data gathered by the gauges located above the guns (immediately above the perforations) with the data from gauges in the 7-inch liner will be presented to show the potential for incorrect interpretation due to the gauge placement. We will also discuss the unseen behavior of flowing gas temperature at perforation depth based on actual temperature data recorded.

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