This paper proposes a variation of ‘slug test’ for sucker-rod pumping oil wells. Application of slug testing simply expedites the buildup process. A slug test is conducted by admitting a slug of reservoir liquid such that the hydrostatic head of the wellbore liquid column balances the reservoir pressure; that is, the well kills itself. Bottomhole pressures (BHP) monitored in such a test have been routinely analyzed by the hydrologists and petroleum engineers alike over the past 35 years.

Although a slug test is typically associated with a new well, the same concept can be extended to pumping wells producing for years. A variation of slug test can be conducted on a pumping well by leaving the casinghead valve open and recording pressures either downhole or by using the acoustic method. The data so gathered lends itself to slug test interpretation.

An analysis of wellbore storage phenomenon arising from flow of a two-phase gas/liquid mixture is presented. The analysis shows that a slug test would allow the pressure buildup process to occur much faster than the conventional buildup method wherein a surface shut-in is required. Two tests conducted on the same well by the two methods, using downhole recorders, demonstrate the value of the proposed method. Reservoir parameters computed from the two tests are in very good agreement; thus, lending credence to the method proposed.

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