Wireline Tool String
The tool string is attached to the rope socket at the end of the wireline. Besides connecting to the wireline, the tool string must also provide:
1, the ability to provide weight so that the wireline is held in tension and can be run into the well at an acceptable speed.
2, the activity to accommodate fairly rapid changes in inclination within the tubing string particularly in deviated wellbores.
3, the ability to provide a jolt upwards or downwards on the work tool by upwards or downwards jarring.
4, the correct running or pulling tool to install or retrieve the wireline component within the tubing string. Alternatively an auxiliary function tool such as a paraffin cutter may be conveyed.
-Stem bar:
When a wireline tool string is run into the well, there are two forces which oppose the tool string:
-the frictional force as the wireline is pulled downwards through the packing elements of the stuffing box.
-a differential force acting upwards on the tool string due to the difference in the plane end areas of the top and bottom of the tool string due to the diameter of the wireline itself.
-Jars:
Since the operation of all wireline equipment is affected by mechanical impact, it is essential that the tool string can deliver the weight of the stem bar as a jolt or jar to the operating tool. This is accomplished by placing a set of jars immediately below the stem.
Most frequently, mechanical jars, are employed and these can be used to create a jarring force in either the upwards or downwards direction. The action is such that these jars are sometimes referred to as stroke jars.
In addition, it is possible to run a set of hydraulic jars immediately above the mechanical jars, but these only provide a jarring capability in the upwards direction.
If hydraulic jars are used in shallow well operations an accelerator is frequently added which helps to maintain a steady pull on the hydraulic jar as it starts to open.
-Knuckle joint:
The knuckle joint is a ball and socket joint which is run above the operating toll and helps to align it with the tubing string.
The alignment is critical, to assist in the centralisation of the operating tool in, for example, the nipple prior to its installation by jarring downwards.
