When do we perform Fishing operations during drilling?

It is better to begin with a definition of Fish.

Imagine that during drilling, a section of the drillstring—located several hundred meters downhole and transmitting rotary torque to the bit—breaks for any reason (which we will not discuss here), causing it to become disconnected from the upper part of the string. Alternatively, part of a logging tool may break and fall to the bottom of the hole. In such cases, and in similar situations, we say that “we have left a Fish in the hole.”

Thus, in drilling operations, a Fish refers to any object or piece of equipment that unintentionally remains inside the wellbore, including tools that accidentally fall into the hole due to human error during drilling operations. Naturally, drilling cannot continue until these items are removed.

Fishing operations are in fact one of the common causes of delays in drilling projects.

The set of activities carried out with special tools to remove the Fish from the well is called Fishing.

Because Fish can have various shapes and forms (for example, part of the drillstring or casing, logging tools, or even a piece of a bit that has broken off), a wide variety of fishing tools have been designed and are used in such operations.

We will not go into the details of each fishing tool here; instead, to help colleagues working in upstream oil and gas contracts who may hear these tool names in technical meetings, we provide a general classification of the most important tools:

1-External Catch Tools

Tools that engage the external diameter of the Fish. Examples include:

• Overshots
• Die Collars (Boxtaps)

 2-Internal Catch Tools

Tools that engage the Fish from the inside. Examples include:

• Taper Tap
• Packer Retriever
• Pears

3- Junk Catch Tools

Tools used to remove debris and broken pieces from the well. Examples include:

• Junk Basket
• Magnet
• Junk Subs

4-Milling & Cutting Tools

• Tools used to grind or cut the Fish.

Fishing operations may take several hours or even several days, depending on several factors such as the type of Fish and the tools selected.

With this introduction, Petrollex Channel sharing with you a training manual prepared in 2004 (1383) by  the Central Iranian Oilfields Company, published by the Training Department, along with Weatherford’s Fishing Operational Guidelines for further study.