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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 977

Last Page: 977

Title: Some Recent Developments in Drill-Stem Test Interpretation Useful to Explorationists in Tight Gas Sand Plays and in Identifying Reservoirs with Linear Geometry: ABSTRACT

Author(s): Hugh W. Reid, Tom B. Davis, Lloyd G. Alexander

Article Type: Meeting abstract


Two major areas of recent development in drill-stem testing are of particular interest to geologists. The first is the use of closed chamber DST's to evaluate the very tight gas sands currently under intense exploration in areas such as Alberta's Deep Basin and various intermontane basins in the United States Rocky Mountain province. Conventional DST's of such zones frequently provide little usable data, especially in very deep wells where the time for gas to fill the drill string, reach surface, and thereby be detected, commonly exceeds allocated flow time. This problem of definitive identification of gas presence and verification of rate is overcome where closed chamber tests are utilized, since downhole gas influx is determined from instantaneous surface pressure chang . Interpretation processes are explained which have enabled initial detection of gas and rate verification, and have sometimes allowed differentiation between truly impermeable and badly damaged zones. Field examples from the Deep Basin of Alberta are shown together with results after completion. Other applications are shown.

The second development is the use of DST data to identify reservoirs with linear flow geometry. Geologic situations where flow into the well bore during a test can be considered linear rather than truly radial include long narrow reservoirs with parallel boundaries such as channel sands, zones bounded by parallel sealing-fault boundaries, or naturally fractured reservoirs where an open fracture intersects the well bore. Many such situations may be identified utilizing simple graphic techniques involving plots of the pressure buildup during shut-in periods versus the square root of various time functions. These plots allow extrapolation to correct reservoir pressure (not possible with conventional Horner plots which assume radial flow, and which sometimes result in false interpretation of depletion).

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Copyright 1997 American Association of Petroleum Geologists