Paper: Drill Stem Test Chart Interpretation And Reservoir Evaluation

The Drill Stem Test (DST) is a temporary well completion, which is made in the early production life of a potential reservoir to determine both the quality and quantity of produced reservoir fluids. This can be done prior to completing the well. The drill stem is used to lower the packer(s), downhole valve assemblies and other auxiliary tools to the bottom of the hole. The packer is a device which expands and effects a seal with the wall of the hole and isolates the zone to be tested from the drilling fluid in the annulus. The surface-operated downhole valve assemblies are devices used to relieve the hydrostatic drilling fluid pressure from the face of the formation to be tested, allowing the produced fluids to enter the drill pipe and be trapped so that they may be recovered and measured at the surface. An upper tool valve allows the formation to produce into the drill pipe for a specified time. The tool can then be closed and the formation buildup pressure can be recorded again for a specified time. The opening and closing of the downhole valve can be repeated for two or more flow times and closed-in times. Other tools and accessories are also used in modern drill stem tests. Accurate pressure data are very necessary for the interpretation of the test and analysis of the tool behavior. During DST"s, two or more subsurface pressure recorders should be used. These provide the means for obtaining accurate reservoir pressure records. One recorder should be located below the packer, in a blanked-off position. Since no fluid should flow past this recorder during the test, it will record the pressures directly from the annulus. The other recorder is in the flow stream above the packer but below the tools and bottomhole choke. This arrangement of recorders is necessary to help insure the detection of any anchor, tool and/or choke which could cause plugging, and for obtaining accurate pressure data. Most downhole pressure recordings are under dynamic rather than static conditions.