The diagram here is just one way a conventional DST may look. It also shows where equipment is run in the testing string.
1. Reverse circulation subs are used to safely circulate out recovered fluids or gas, there are two types of these subs and are available in any connection:
a: Pump-out Sub: the port is opened by applying pressure to the inside of the drill string and pumping out the disk. Used in case of an obstruction in the string or where dropping a bar on the Knockout sub is not an option.
b: Knockout Sub: the ports are opened by dropping a heavy bar/rod inside the Test Head and breaking the pins in the sub which opens the string to the annulus, so reverse circulation can start.
2. Crossover Sub, BJ's DST has xo-subs to x-over to any connection.
3. Flow-thru Subs are used for a variety of reasons, here it is used to catch the bar used in reversing out. Also used as spacer in the interval, or as a place to attach an Electronic Gauge inside or outside.
4. Recorder Carrier, used to carry the mechanical recorders during the test. Can be placed anywhere in the test tool, here it is placed to read the fluid in the pipe without interference from the formation, a recorder in this location is ideal for detecting leaks in the string during the DST.
5. Rotational Shut-in Tool, this is a valve operated from the rig floor used to open and shut the tool during the DST. Available in 2-flows & 2 closes or 3-flows & 3-closes.
6. Sample Chamber, traps pressure, the last fluid and/or gas flowing thru the tool just before the tool is shut for the last time.
7. Hydraulic Tool, this is also a valve, it is closed for the trip in the hole and is set to open in 2 minutes with 30,000# set on it, depending on temperature. It gives an indication at surface when it opens by showing a gain of 7-10,000# on the weight indicator. Weight can be put on for short periods of time without opening the tool before it is time, as soon as the tool is picked up to string weight again the cycle starts over. This gives you a chance to work through tight spots in the hole.
8. Bypass Assembly, it is part of the Hydraulic Tool, the Bypass is open while tripping pipe, it allows displaced annulus fluid to flow thru the perf and thru the I.D. of the packers, safety joint, jars and inside recorder and out the ports of the assembly on the trip in and out of the hole. This minimizes the surging and swabbing effect the packers have on the hole during tripping. It closes at the same time the hydraulic tool opens to begin testing. After the test and before pulling loose the Bypass is opened again to equalize the pressure differential above and below the packers.
9. Recorder Carrier, here it is used to carry the inside pressure recorder. Multiple recorders can be placed here if desired, i.e. electronic, mechanical, all would be inside recorders.
10. Jars, available in various sizes. Aids in pulling loose the DST and working through bad hole conditions.
11. Safety Joint, left hand release, run directly above the packers. Should the tool become stuck in the hole, the Safety Joint is designed to break at 40% of the make up torque. Since using a string shot on a wire-line to back off a tool will not work from the top of the tool to the top of the Jars, this is the place in the string designed to be backed off mechanically.
12. Packers, used to seal off the annulus above or below (straddle test) the formation being tested. BJ's DST. has packers available to fit any hole size. Long packers for poor packer seats and deeper tests, standard length packers for good seats and shallower tests. Extra high temperature, oil base rubber is also available for temperatures above 280° F, or for use in oil base mud.
13. Perforated Anchor, heavy walled anchor (5”OD x 2.375”ID) Since a conventional test sets on the bottom of the hole, the anchor is used to achieve the desired interval from the bottom of the hole to the packer seat. The perforations allow the formation fluid or gas to enter the tool and pipe.
14. Blank-off sub, blanks off the I.D. of the tool, is also used to hang an Outside Electronic Gauge from. Any recorder below the Blank-off sub is an outside recorder.
15. Electronic Recorder, BJ’s DST uses Sunada Electronic Recorders, the recorders can be booted to take a pressure and temperature reading for as low as every 1 second if needed, the standard setting used is one sample every 5-15 seconds. The data is downloaded at the rig to a disk and can be E-mailed almost immediately.
16. Thermometer, mechanical thermometer reads the highest temperature achieved during the test.
17. Outside Recorder, placed here is the outside electronic recorder.
18. Bull-nose, used at the bottom of the tool to help guide the tool in the hole and keep out anything that might plug the tool.
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BJ's Drill Stem Testing