Drilling & Well Completion

Sidetrack

Sidetracking: A Second Chance in Drilling & Well Completion

In the world of oil and gas exploration, drilling a wellbore is a complex and expensive undertaking. Sometimes, unforeseen circumstances can lead to complications that render the initial wellbore unusable. This is where sidetracking comes in – a technique that allows drilling engineers to salvage the situation and continue their quest for hydrocarbons.

What is Sidetracking?

Sidetracking refers to the process of drilling a new wellbore, called a sidetrack, from an existing wellbore. This technique is typically employed when the initial wellbore encounters:

  • Unforeseen geological formations: A well may encounter impenetrable rock layers, faults, or other unexpected geological features that hinder further drilling.
  • Lost circulation: The drilling fluid may be lost into the surrounding formation, making it difficult to maintain pressure and control the drilling process.
  • Stuck pipe: The drill string may become stuck inside the wellbore, rendering it impossible to continue drilling.
  • Wellbore collapse: The wellbore walls may collapse, creating instability and compromising the integrity of the well.

Types of Sidetracking:

There are two primary types of sidetracking:

  1. Conventional Sidetracking: This involves drilling a new wellbore from the existing wellbore at a specific depth, typically at the bottom of the initial wellbore. The sidetrack is then drilled in a new direction to reach the target zone.
  2. Parallel Sidetracking: In this type, the new wellbore is drilled parallel to the original wellbore, typically at a shallower depth. This technique is used when the primary wellbore needs to be re-entered or when the target zone is located at a different level.

Why Choose Sidetracking?

Sidetracking offers several advantages over completely abandoning the initial wellbore and starting afresh:

  • Cost Savings: Sidetracking allows drilling engineers to utilize the existing wellbore structure and infrastructure, significantly reducing the time and cost required to reach the target zone.
  • Enhanced Safety: Sidetracking minimizes the risks associated with re-drilling the entire wellbore, reducing the possibility of encountering the same geological issues that led to the initial problems.
  • Increased Efficiency: The existing wellbore acts as a guide for the new wellbore, allowing for a more efficient and accurate drilling process.

The Challenges of Sidetracking:

Sidetracking isn't without its challenges:

  • Wellbore Integrity: The existing wellbore must be stable enough to support the drilling operations of the sidetrack.
  • Wellbore Geometry: The size and shape of the existing wellbore can limit the size and direction of the sidetrack.
  • Technical Expertise: Sidetracking requires specialized equipment and highly skilled engineers to execute the drilling process successfully.

Conclusion:

Sidetracking is a valuable tool in the oil and gas industry, providing a second chance to reach valuable hydrocarbon reserves despite unexpected challenges encountered during initial drilling. By leveraging existing infrastructure and technical expertise, sidetracking offers a cost-effective and efficient solution for overcoming drilling obstacles and maximizing the success of exploration projects.

Test Your Knowledge

Sidetracking Quiz

Instructions: Choose the best answer for each question.

1. What is sidetracking in the context of drilling and well completion?

a) Drilling a new wellbore entirely independent of any existing wellbores. b) Drilling a new wellbore from an existing wellbore to reach a different target zone. c) A technique to increase the diameter of an existing wellbore. d) A method used to stabilize the wellbore walls during drilling.

Answer

b) Drilling a new wellbore from an existing wellbore to reach a different target zone.

2. Which of the following scenarios is NOT a common reason for using sidetracking?

a) Encountering impenetrable rock layers. b) Successful completion of the initial wellbore. c) Lost circulation of drilling fluid. d) Stuck pipe in the wellbore.

Answer

b) Successful completion of the initial wellbore.

3. What is the key difference between conventional and parallel sidetracking?

a) Conventional sidetracking is more expensive. b) Parallel sidetracking is used for deeper targets. c) Conventional sidetracking drills the new wellbore from the bottom of the existing wellbore. d) Parallel sidetracking is less risky than conventional sidetracking.

Answer

c) Conventional sidetracking drills the new wellbore from the bottom of the existing wellbore.

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

a) Cost savings compared to completely abandoning the initial wellbore. b) Reduced risk of encountering the same drilling issues. c) Increased efficiency due to the existing wellbore acting as a guide. d) Guaranteed success in reaching the target zone.

Answer

d) Guaranteed success in reaching the target zone.

5. What is one of the main challenges associated with sidetracking?

a) The need for specialized equipment. b) The availability of skilled engineers. c) The possibility of encountering unforeseen geological formations. d) All of the above.

Answer

d) All of the above.

Sidetracking Exercise

Scenario: An oil company is drilling a well to reach a hydrocarbon reservoir at a depth of 10,000 feet. However, at a depth of 6,000 feet, the drill string gets stuck due to a geological formation. The company decides to implement sidetracking.

Task: Describe the two possible types of sidetracking that could be used in this scenario and explain which option would be more suitable and why.

Exercice Correction

The company could choose between:

1. **Conventional Sidetracking:** Drill a new wellbore from the bottom of the existing wellbore (at 6,000 feet) in a new direction to reach the target reservoir at 10,000 feet.

2. **Parallel Sidetracking:** Drill a new wellbore parallel to the existing wellbore at a shallower depth, aiming to reach the reservoir at a different horizontal position.

In this scenario, **conventional sidetracking** would be more suitable. This is because the objective is to reach the same target reservoir at the same depth. Conventional sidetracking allows for a direct path to the target zone, avoiding the need to re-drill to the same depth as the original wellbore. Parallel sidetracking would be less effective in this case as it would potentially lead to a different horizontal location within the reservoir.

Books

  • Petroleum Engineering Handbook: This comprehensive handbook offers detailed information on various aspects of drilling, including sidetracking techniques.
  • Drilling Engineering: A Comprehensive Approach: This book provides in-depth knowledge of drilling practices and technologies, including a section on sidetracking and its applications.
  • Well Completion Engineering: This book focuses on the post-drilling phase and covers different techniques for completing wells, including sidetracking.

Articles

  • "Sidetracking: A Cost-Effective Way to Achieve Wellbore Success" by SPE: This article delves into the economic and operational benefits of using sidetracking techniques in drilling operations.
  • "Sidetracking Techniques for Challenging Wellbore Conditions" by Oilfield Technology: This article explores various sidetracking techniques and their applications in different drilling scenarios.
  • "Sidetracking: A Tool for Re-Entry and Reservoir Access" by Schlumberger: This article highlights the role of sidetracking in re-entering wells and accessing different reservoir zones.

Online Resources

  • SPE (Society of Petroleum Engineers): The SPE website offers a vast library of publications, technical papers, and presentations on sidetracking and other drilling-related topics.
  • *Schlumberger: * This leading oilfield services company provides valuable insights into various drilling technologies, including sidetracking, on its website.
  • Baker Hughes: Another major oilfield services company, Baker Hughes offers resources on drilling and well completion technologies, including information on sidetracking.

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  • "Sidetracking well completion"
  • "Sidetracking cost analysis"
  • "Types of sidetracking"
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Techniques

Chapter 1: Techniques

Sidetracking Techniques: A Guide to Drilling Beyond Obstacles

Sidetracking, as discussed previously, is a valuable tool in the oil and gas industry, allowing engineers to navigate unforeseen drilling complications. This chapter delves deeper into the various techniques employed in sidetracking, providing a comprehensive understanding of the process.

1.1 Conventional Sidetracking:

  • Process: This method involves drilling a new wellbore from the existing wellbore at a specific depth, typically at the bottom of the initial wellbore. This new wellbore, the sidetrack, is then drilled in a new direction to reach the target zone.
  • Tools:
    • Whipstock: A wedge-shaped tool placed inside the existing wellbore to initiate the new bore path.
    • Jetting: Using high-pressure jets to create a path for the drill bit.
    • Directional Drilling: Utilizing advanced drilling tools and techniques to control the direction and trajectory of the sidetrack.
  • Advantages:
    • Relatively straightforward execution.
    • Suitable for various geological challenges.
  • Disadvantages:
    • Requires sufficient space at the bottom of the initial wellbore.
    • May be limited in terms of directional changes.

1.2 Parallel Sidetracking:

  • Process: The new wellbore is drilled parallel to the original wellbore, typically at a shallower depth. This method is preferred when re-entering the primary wellbore or targeting a zone at a different level.
  • Tools:
    • Pilot Hole: A small hole drilled to establish the path for the sidetrack.
    • Casing: Steel pipes used to support and seal the wellbore.
  • Advantages:
    • Allows for re-entry into the existing wellbore.
    • Enables targeting zones at different depths.
  • Disadvantages:
    • May require larger wellhead structures.
    • May not be suitable for complex geological formations.

1.3 Other Techniques:

  • Open-hole Sidetracking: Drilling the sidetrack directly through the existing wellbore. This technique is risky and is only used in specific circumstances.
  • Cased-hole Sidetracking: Drilling the sidetrack through a casing string that has already been installed. This method offers greater stability and control.

1.4 Considerations:

  • Wellbore Integrity: The existing wellbore must be stable and able to withstand the pressure and forces associated with sidetracking.
  • Wellbore Geometry: The size and shape of the existing wellbore impact the feasibility of sidetracking.
  • Target Zone Location: The location of the target zone dictates the direction and length of the sidetrack.
  • Drilling Fluids: The type and properties of drilling fluids used are crucial for maintaining wellbore stability and minimizing formation damage.

1.5 Conclusion:

Choosing the appropriate sidetracking technique depends on the specific circumstances of each well. By understanding the various techniques and their advantages and disadvantages, engineers can choose the most effective method to overcome drilling obstacles and achieve exploration success.

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