Drill stem test (DST) is the conventional method of formation testing and reservoir evaluation which obtains reservoir data under dynamic (rather than static) conditions. A DST is essentially a temporary completion, a method of evaluating reservoir formations without costly and time-consuming completion procedures.
The basic drill stem test tool consists of a packer or packers, valves or ports that may be opened and closed from the surface, and two or more pressure-recording devices. The tool is lowered on the drill string to the zone to be tested. The packer or packers are set to isolate the zone from the drilling fluid column.
The valves or ports are then opened to allow for formation flow while the recorders chart static pressures. A sampling chamber traps clean formation fluids at the end of the test.
Analysis of the pressure charts is an important part of formation testing.
Data attainable from a Drill Stem Test
Normal data recovery from a Drill Stem Test includes items such as fluid recovery and description, blow descriptions test times, mud and hole data and the pressure/time data as recovered from the chart record. These items are reported from the field and recorded on a field data sheet or envelope.
In addition to field data (direct information), additional reservoir characteristics may be calculated utilizing the test data recovered in the field (indirect information). Some of these reservoir characteristics are: