Depth correlation before perforation is crucial in reservoir testing, to minimize the uncertainties about the reservoir being tested. Currently, three main methods are used to correlate to depth: simple pipe tally, tag of a known element in the well, or a wireline gamma ray (GR) log—which is the most accepted method, owing to its precision and track record. Wireline GR correlation, however, requires additional time (6 to 8 hours), translating into cost for the operator. We describe a new depth correlation tool, which is mounted directly in the drillstem test (DST) string and is enabled by a downhole wireless acoustic telemetry system, that provides correlation algorithm in real time without the need for extra wireline intervention. The introduction of a wireless-enabled GR measurement into the DST string radically changes the workflow for DST operations and results in significant reduction of rig time, as shown by one of our latest job campaigns in Qatar.

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