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Drill-stem Testing

From RitchieWiki

Petroleum Processes

Drill-stem testing (DST) is a procedure used in the petroleum industry to determine the productive capacity,and permeability of a potential petroleum reservoir zone. It is comprised primarily of a flow test on isolated rock formations that indicate the possibility and presence of an oil reservoir. DST, is used primarily on exploratory oil wells and gas wells, to ascertain their commercial productivity.[1]

A typical test is made up of several flow and shut in periods or sequences during which reservoir data is recorded. The most common sequence for a DST test consists of short flow periods of five to ten minutes (pre-flow). This may be followed by a "buildup" period of an hour or more to determine the initial reservoir pressure and then a longer flow period (main flow). This is a longer    time of four to 24 hours to determine both permeability thickness and flow potential. Then the well would be shut in for a longer period  which enables  a more precise look at the reservoir variables (main flow). [2] The main objectives behind drill-stem testing is to maximize oil reserves, accelerate the exploration schedule and reduce oil production costs and risks associated with drilling.[3]

[edit] Process

A DST tool is attached to the bottom of the drill string and lowered to a point opposite the formation to be tested. The DST tool is equipped with expandable seals (packers) that permit the formation being tested to be isolated from the rest of the borehole. The drill pipe is also emptied (run in dry) of all drilling mud so formation fluid can enter into the drill string. When the flow and shut-in time periods have been done, openings(flow valve) in the DST tool are closed off and the drill string is brought up to the surface. The contents inside the drill string are measured. The amount of gas and oil that flow into the drill string during the test and the recorded pressures are analyzed to determine the productive capacity of the formation. Similar type tools exist that can also seal off and test a formation inside a cased well bore or can provide a small sample of the reservoir fluid being produced.[4]

[edit] References

  1. Drillstem test. Schlumberger Oilfield Glossary. 06-04-2009.
  2. Drillstem test. Schlumberger Oilfield Glossary. 06-04-2009.
  3. Drillstem Testing. Northstar Drillstem Testers. 06-04-2009.
  4. Petroleum Production. Well logging and drill-stem testing. Encyclopedia Britannica. 04-06-2009.

www.horizontalwelltesting.com  Ron Craik