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Glossary of Technical Terms Used in Drilling & Well Completion: overshot

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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.

Test Your Knowledge

Overshot Quiz

Instructions: Choose the best answer for each question.

1. What is the primary function of an overshot in oil and gas drilling?

a) To prevent blowouts. b) To retrieve lost or stuck equipment from the wellbore. c) To drill through hard rock formations. d) To measure the depth of the well.

Answer

b) To retrieve lost or stuck equipment from the wellbore.

2. What type of friction device is commonly used in overshots?

a) A hook b) A magnetic clamp c) A basket or spiral grapple d) A hydraulic piston

Answer

c) A basket or spiral grapple

3. How does a basket-type overshot secure the lost equipment?

a) Using a strong magnet b) By applying pressure with a hydraulic piston c) With spring-loaded jaws that grip the outside of the pipe d) By using a series of spiral blades

Answer

c) With spring-loaded jaws that grip the outside of the pipe

4. Which of the following is NOT an advantage of using overshots?

a) Versatility b) Reliability c) High cost d) Cost-effectiveness

Answer

c) High cost

5. What factor should be considered when choosing an overshot?

a) The color of the lost equipment b) The size of the lost equipment c) The weight of the drilling rig d) The weather forecast

Answer

b) The size of the lost equipment

Overshot Exercise

Scenario: You are working on an oil rig and a piece of drill pipe gets stuck in the wellbore. You need to retrieve the lost pipe using an overshot.

Task: Choose the most appropriate type of overshot for this situation, considering the following:

  • The stuck drill pipe is 5 inches in diameter.
  • The well depth is 10,000 feet.
  • The well conditions are relatively stable with moderate pressure and temperature.

Choices:

  • Basket overshot
  • Spiral grapple overshot
  • Combination overshot

Justify your choice and explain why the other options might not be suitable.

Exercise Correction

The most appropriate overshot for this situation is a **Basket overshot**. Here's why:

  • **Size:** A basket overshot is designed to handle a range of pipe sizes, making it suitable for the 5-inch drill pipe.
  • **Well conditions:** The moderate pressure and temperature conditions in the well are well within the operating range of a basket overshot.
  • **Spiral Grapple:** While spiral grapples are effective, they might be less suitable for a relatively stable wellbore. They work best in challenging conditions with a high risk of the fish getting stuck.
  • **Combination Overshot:** This type of overshot offers versatility, but it might be overkill for this scenario. The basket overshot should be sufficient for the given conditions.

Books

  • Petroleum Engineering Handbook: This comprehensive handbook covers various aspects of oil and gas production, including well completion and fishing operations. You'll find chapters dedicated to fishing tools and techniques, including overshots.
  • Drilling Engineering: This book delves deeper into the technical aspects of drilling operations, including wellbore challenges, fishing procedures, and the use of overshots.
  • Well Completion Engineering: This book focuses specifically on the processes involved in completing a well after drilling, including wellbore equipment, fishing techniques, and tools like overshots.

Articles

  • "Fishing Tools and Techniques" by [Author Name], [Journal Name]: Search for journal articles in publications like the Journal of Petroleum Technology (JPT) or SPE (Society of Petroleum Engineers) publications. Look for articles specific to fishing tools, overshots, and case studies of their use.
  • "Overshot Design and Applications" by [Author Name], [Conference Proceedings]: Check for conference proceedings from SPE or other relevant industry conferences where engineers present research on overshot technology and applications.
  • "Case Study: Successful Retrieval of Lost Tubing Using an Overshot" by [Author Name], [Industry Publication]: Search for case studies in industry magazines or websites that showcase successful applications of overshots in specific situations.

Online Resources

  • Society of Petroleum Engineers (SPE): The SPE website offers a wealth of resources, including technical papers, conference proceedings, and industry news related to drilling, completion, and fishing operations.
  • Oilfield Wiki: This online platform provides detailed information on various oilfield equipment and processes, including fishing tools and techniques.
  • Halliburton, Schlumberger, Baker Hughes websites: Major oilfield service companies offer comprehensive resources on their fishing tools and services, including overshots.

Search Tips

  • Combine keywords: Use keywords like "overshot," "fishing tool," "well completion," "drilling operations," "lost equipment," "oil and gas," and specific brands or manufacturers.
  • Use quotation marks: Enclose specific phrases like "basket overshot" or "spiral grapple overshot" in quotation marks to get more precise results.
  • Refine your search: Use operators like "site:spe.org" to limit your search to a specific website, or "filetype:pdf" to find PDF documents.
  • Explore images and videos: Use Google Images and YouTube to visualize different types of overshots and their functionalities.
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