Wire-line Stem or Sinker bar is used as the weight to run a wire-line string (tool-string) down the well and provides the weight required during jarring operations against well pressure and stuffing box friction.
Formula / a rule of thumb to determine the weight of a solid steel stem is:
O.D² x 8/3 = weight (pounds per feet)
The impact force increased by increasing the stem weight that it is delivered by the jars. Do not overweight the tool-strings, as excessive mass dampens the feel and premature shearing of the pins can occur.
Never grip on the fishing neck or this will damage the sharp edge. Should be used and provided flat for wrenches.
Do not lubricate the tool-string threads- they will unscrew down hole during extended jarring. All connection should be clean and dry.
The standard lengths of stem are 2 feet, 3 feet, and 5 feet.
Nominal O.D of stems are 3/4 inches, 1 inches, 1-1/4 inches, 1-1/2 inches, 1-7/8 inches, 2-1/8 inches, 2-1/2 inches.
There are 3 types of stem: solid stem, roller stem, lead filled stem.
The Roller Stem is a valuable, sometimes essential, addition to tool-string for deviated wells to reduce the frictional losses against the tubing wall.
The Lead filled Stem provides massive weight for the same diameter and length. It has a regular steel pin and box, and a tubular steel outer barrel. Inside of stem is filled with lead to provide maximum density.
Filled stem is used primarily to run flowing pressure surveys to obtain maximum weight and minimum cross-sectional area. It is protect against floating or being blown up the hole by pressure surges.
Other high density heavy weight stems which are available include: tungsten, uranium, mallory filled (mercury alloy).
Do not use Lead Filled Stem for jarring as the lead will tend to creep downwards and split the outer barrel.
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