Wireline tool such as logging tool, slick line tool can be stuck in the hole therefore we need to understand about wireline recovery tool. This article demonstrate typical wireline fishing / recovery tool. Common wireline tool issues center around the cable being tangled or wadded in the hole, as well as the fact that attempts at fishing can pull the wireline out of the rope socket or part, further complicating tool retrieval.
Stuck Cable or Tools
As soon as a wireline assembly becomes stuck, the operator will need to determine whether the problem is in the cable or the tool. Usually, one would apply normal logging tension on the cable and allow it to sit for a few minutes. During this time, four things should be recorded:
- the current depth of the tool
- the type and size of the cable
- the surface tension of the cable just prior to becoming stuck
- the cable-head’s weakpoint rating
The cable will be marked at the rotary table, and a T-bar clamp will also be securely fitted to the cable just above the table. Should the cable break, then the clamp holds on to the cable end at the surface, so that the whole cable does not fall down the hole and cause additional blockage. The operator will hen need to apply 1000 lbf of tension on the cable, and make a note of the distance that the cable mark moves at the rotary table. This figure shows the stretch produced in the elastic cable. It is then possible to estimate the length of free cable, using a stretch chart or from prior knowledge of the cable’s stretch coefficient. Should the length of free cable be the same as the current logging depth, then the problem does not lie with the cable; rather, the tool is stuck, and not the cable. If the length of free cable is less than current logging depth, then the cable is stuck at some higher point in the hole.
If it is the tool which is stuck, and not the cable, then pulling on the cable will cause one of three results. The tool may come free, the weakpoint can break and the tool will remain in the hole but the cable can be removed, or the cable will break at the point of maximum tension.
Causes of Sticking
When the cable cuts through mudcake, differential pressure sticking may occur. This is because one side of the cable is exposed to some degree of formation pressure, whereas the other is exposed to the hydrostatic mud column. Due to this significant difference in pressure, the cable will be pressed harshly into the formation, and friction against the formation stops the cable from moving any longer. Other reasons why sticking may occur include ledges, particularly severe doglegs, borehole caving, or the borehole becoming corkscrewed. As the length of the tool increases, as well as when there has been a long amount of time since the last conditioning trip, the chances of sticking will go up.
When a wireline tool or cable gets stuck, there are several different ways that they can be recovered.
One option is a side-door overshot as shown in Figure 1. This method is similar to a regular overshot, except that it features a removable side door, so that the tool can be put together around the wireline at the well head itself. It is then possible to run the tool on some tubing or on the drillpipe, downhole alongside the wireline in order to make direct contact with the tool. This stops the wireline from being at risk of parting.
It is not recommended that side-door overshots are used with deep open hole intervals. This is because it introduces the potential for keyseating, or differential sticking in the mud cake.
Throughout modern drilling, the most successful method to retrieve stuck logging tools is through the cut-and-thread method. This involves cutting the wireline at the surface, and then threading it through a pipe string while the pipe is lowered, until it engages with the logging tool. The line must be secured at the surface, and rope sockets need to be fitted to each end to form a spearhead both emerging from the top of the well, and a spearhead overshot at the logging end. A stand of pipe will then be hung in the derrick, allowing enough of an overshot at the bottom to catch the logging tool, or at least the wireline rope socket. When the upper end of the line is spooled down through the interior of the pipe until the overshot connects with the spearhead at the bottom, then the pipe will be run into the hole. This is repeated with additional stands until the bottom of the string is close enough to the fish. When this is achieved, the spearhead overshot can be disengaged and the overshot can be circulated clean, before it engages with the tool. When the fish has been grasped securely, the wireline will be pulled free from the rope socket, and then spooled out of the hole, and the tool itself recovered with the fishing string. Although the cut-and-thread method takes a lot of time, and comes with a certain amount of risk, it vastly improves the chances of recovering the wireline and tool fully, and is much quicker than trying to engage with the wireline in an open hole.
If it is not possible to use either a side-door overshot or a cut-and-thread, then an alternative is to break the weakpoint, and then recover the cable and use the drill pipe to fish for the logging tool. If tool recovery is not an option, then a last resort is to push it to the very bottom of the hole, and then plug it using cement.
Wireline Barb (Rope Spear)
Wirelines that are wadded or tangled can be retrieved with a wireline barb or rope spear. This penetrates the debris, engages with it, and then allows the debris to be pulled away, as shown in Figure 2. This is one of the most basic forms of fishing tool, and gives strong results when used in the right way.
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