Straddle Test Tool Configuration
A Conventional Straddle Test Tool sets on the bottom of the hole or a cement plug. A straddle test is used when a potential pay zone needs to be isolated both above and below the zone. Other types of straddle test tools such as a Hook Wall tool are designed to set against the wall of the hole, where the Hook Wall tool would be placed somewhere under the bottom set of packers depending on the gauge of the hole. An Inflatable Straddle Test is one that uses inflatable packers that once inflated, set against the wall of the hole. In the Williston Basin the conventional straddle test is the most commonly used straddle test, and is the most reliable.
The diagram at the left shows one way a conventional straddle may look. The tool above the Hanger Sub is made up similar to the tool above the packers in the diagram of the Conventional Test Tool.
19. Hanger Sub, this sub is used hang the equalization pipe from. It ports the annulus pressure above the packers to the equalization pipe. It also has a flow through I.D. allowing Formation fluid to pass through to the tool above.
20. Pressure Equalization Pipe (By-pass Pipe), this pipe transfers the hydrostatic pressure above the top packers to below the bottom packers, thus equalizing the pressure above and below the tested interval and minimizing the pressure differential across the bottom packers when pulling loose. When using this pipe on a straddle test it will give you an indication at surface if the bottom packers are holding, it also makes it possible to pull the tool loose when the test is finished by minimizing the pressure differential. Without this pipe at depths of 8,000’ or more it is almost impossible to pull a straddle test loose without extensive jarring or pull rates that exceed 100,000# over string weight. BJ's DST. recommends using this pipe below 8,000’ in depth or when hydrostatic pressure reaches 4200 PSI.
21. Receiver Sub, is run in the interval and is there for the equalization pipe to sting into. From there the hydrostatic pressure is directed below the tested interval.
22. Standard Packer Assembly, a shorter rubber than the long packer, the standard packer is 20” long and the long element is 36” long.
23. Blank Anchor, (5” O.D. x 2 3/8” I.D.) used for spacing an interval, or where outside annulus fluid is not wanted in the I.D. of the tool. Same as a 5” O.D. drill collar only shorter and comes in various lengths.
24. Recorder Carrier, used here to read pressure under the tested interval, shows equalization pipe working or in the case of no equalization pipe it shows if the bottom packers held during the straddle test.
(If no equalization pipe is used)
A Blank-off Sub (14) would be used in place of the Receiver Sub (21) and no Hanger Sub (19) would be needed. This would seal off the I.D. below the interval, which is needed during a straddle test.
25. Drill Collars, used as spacing depending on length needed. (optional)
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BJ's Drill Stem Testing