Also known as Drill Stem Testing, a DST is a procedure to determine the productive capacity, pressure, permeability or extent of an oil or gas reservoir. A DST is essentially a flow test, which is performed on isolated formations of interest to determine the fluids or gases present and the rate at which they can be produced. It is a valuable and cost-effective method of determining the viability and commercial productivity of a well within an accelerated time line as well as providing lower financial risk compared to conventional well testing methods.
A basic DST consists of:
Packer/s: which act as an expanding plug to be used to isolate sections of the well for the testing process;
Valves: that may be opened or closed from the surface during the test;
Recorders: used to document pressure during the test; and a
Sampler: which traps a sample of formation fluids from the last flow (used for analysis).
In addition to packers, a down hole valve is used to open and close the formation to measure reservoir characteristics such as pressure and temperature which are charted on down hole recorders within the BHA.
Drillstem testing can be performed on wells with both open and cased holes. An open hole DST is usually more economical because it's performed before casing is run.