Dst A Tehcnique For Interpretation

A drill stem test (DST) is a procedure for isolating and testing the surrounding geological formation through the drill stem. The test is a measurement of pressure behavior at the drill stem and is avaluable way to obtain important sampling information on the formation fluid and to establish the probability of commercial production.
In oil and natural gas extraction, the drill stem includesthe drill pipe, drill collars, bottomhole assembly, and drill bit. During normal drilling, fluidis pumped through the drill stem and out the drill bit. In a drill stem test, the drill bit is removed, adrill stem test tool is added, and fluid from the formation is recovered through the drill stem, while several measurements of pressure are being made.[1]
The basic drill stem test tool consists of apacker or packers, valves or ports that may be opened and closed from the surface, and two or more pressure-recording devices. (A packer is an expanding plug which can be used to seal off sections ofthe open or cased well, to isolate them for testing.[2]) The drill stem test tool is lowered on the drill pipe to the zone to be tested. The packer or packers are set to isolate the zone from thedrilling fluid column, the tester valve is opened, and testing begins.
History
Working in El Dorado, Arkansas, in the 1920s, E.C. Johnston and his brother M.O. Johnston developed the first drill stemtester and ran the first commercial drill stem test in 1926. In April 1929, the Johnston Formation Testing Corporation was granted a patent (U.S. Patent 1,709,940) and they subsequently refined thetesting system in the early 1930s.[3]
In the 1950s, Schlumberger introduced a method for testing formations using wireline. The Schlumberger formation-testing tool, placed in operation in 1953, fired ashaped charge through a rubber pad that had been expanded in the hole until it was securely fixed in the hole at the depth required. Formation fluids flowed through the perforation and connecting...