overshot

Overshot: A Lifeline in Drilling & Well Completion

In the unpredictable world of oil and gas drilling, encountering a "fish" – a lost or stuck piece of equipment in the wellbore – is a common challenge. While a variety of fishing tools exist, one of the most reliable and versatile options is the overshot.

What is an Overshot?

An overshot is a specialized fishing tool designed to retrieve lost or stuck tubing, drill pipe, or sucker rods from the wellbore. It's attached to the end of a string of tubing or drill pipe and lowered down the well. The key feature of an overshot is a friction device, typically a basket or a spiral grapple, that engages with the outside wall of the lost pipe. This grip allows the fish to be lifted and pulled back to the surface.

How it Works:

1. Lowering the Overshot: The overshot is attached to the end of the tubing or drill pipe and lowered down the well.
2. Engaging the Fish: As the overshot reaches the fish, the friction device engages with the outside wall of the lost pipe. The basket-type overshot utilizes spring-loaded jaws that grip the pipe, while the spiral grapple uses a series of spiral blades to secure the fish.
3. Retrieving the Fish: Once the overshot has secured the fish, the string is slowly lifted. The friction device maintains a tight grip on the lost pipe, allowing it to be pulled back to the surface.

Advantages of Overshots:

• Versatility: Overshots can be used to retrieve a wide variety of lost equipment, including tubing, drill pipe, and sucker rods.
• Reliability: The friction device design ensures a secure grip on the fish, minimizing the risk of losing the fish again.
• Cost-Effective: Compared to other fishing techniques, overshots are relatively inexpensive.

Types of Overshots:

• Basket Overshots: These overshots feature spring-loaded jaws that grip the outside of the pipe.
• Spiral Grapple Overshots: These overshots use a series of spiral blades that engage with the pipe's outer wall.
• Combination Overshots: These overshots combine features of both basket and spiral grapple designs.

Considerations for Choosing an Overshot:

• Fish Size: The size of the lost equipment will determine the size and type of overshot needed.
• Well Conditions: The conditions of the wellbore, such as the depth, temperature, and pressure, must be considered when choosing an overshot.
• Experience and Expertise: The successful use of an overshot requires experience and expertise.

Conclusion:

The overshot is an invaluable tool in the oil and gas industry, offering a reliable and efficient solution for retrieving lost equipment. Its versatility, cost-effectiveness, and relative ease of use make it a cornerstone of fishing operations, ensuring that lost equipment can be salvaged and well operations can continue smoothly.