Drilling & Well Completion

run casing

Running Casing: A Critical Step in Drilling & Well Completion

Running casing, also known as "running pipe," is a crucial stage in both drilling and well completion operations. It involves carefully lowering a string of steel casing into the borehole, creating a robust and sealed conduit that protects the wellbore, prevents fluid loss, and supports the well structure.

Why Run Casing?

Casing serves several critical functions in drilling and well completion:

  • Wellbore Stability: Casing provides structural support to the wellbore, preventing collapses and ensuring stability. This is especially important in areas with challenging geological formations.
  • Fluid Control: Casing creates a barrier between different formations, preventing the mixing of fluids and ensuring the efficient flow of production fluids.
  • Isolation of Zones: Casing can isolate specific zones within the wellbore, allowing for selective production or injection of fluids.
  • Protection from Corrosion: The protective coating on the casing prevents corrosion and extends the well's lifespan.
  • Enhanced Safety: Casing helps to contain pressure within the wellbore, preventing blowouts and ensuring worker safety.

The Running Casing Process:

Running casing involves a sequence of steps:

  1. Preparation: The casing string, which consists of individual sections of pipe joined together, is prepared by attaching various components like a running shoe, centralizers, and a casing head.
  2. Lowering the String: The prepared casing string is carefully lowered into the borehole using a drilling rig's hoisting system. The process is closely monitored and controlled to ensure smooth and efficient deployment.
  3. Cementing: Once the casing reaches its desired depth, cement is pumped into the annulus (the space between the casing and the borehole wall). This creates a strong bond between the casing and the formation, ensuring the well's integrity.
  4. Testing: After cementing, the casing is pressure tested to ensure its integrity and confirm the successful creation of a sealed system.

Types of Casing:

There are various types of casing used in drilling and well completion, each designed for specific functions and conditions:

  • Conductor Casing: The first string of casing to be run, providing initial wellbore stability and protecting the surface environment.
  • Surface Casing: Provides isolation of freshwater aquifers and protection of surface environment.
  • Intermediate Casing: Used to isolate specific formations and support the wellbore further.
  • Production Casing: The final string of casing, designed to produce hydrocarbons or other fluids from the reservoir.

Challenges in Running Casing:

Running casing can pose challenges, including:

  • Difficult Formations: Running casing in complex geological formations, such as those containing shale or tight formations, can be challenging.
  • Pressure Control: Maintaining pressure control during the casing operation is crucial to prevent blowouts and accidents.
  • Casing Integrity: Ensuring the casing's integrity is paramount to prevent leaks and ensure the well's long-term performance.

Conclusion:

Running casing is a critical step in drilling and well completion operations, requiring careful planning, execution, and monitoring. The process ensures wellbore stability, fluid control, and protection, contributing significantly to successful and efficient hydrocarbon production or other well operations. Understanding the intricacies of running casing is crucial for anyone involved in the oil and gas industry.

Test Your Knowledge

Running Casing Quiz:

Instructions: Choose the best answer for each question.

1. What is the primary function of casing in drilling and well completion?

(a) To provide a conduit for drilling fluid circulation. (b) To protect the wellbore from collapse and fluid loss. (c) To facilitate the installation of production equipment. (d) To increase the production rate of the well.

Answer

(b) To protect the wellbore from collapse and fluid loss.

2. Which type of casing is typically used to isolate freshwater aquifers?

(a) Conductor Casing (b) Surface Casing (c) Intermediate Casing (d) Production Casing

Answer

(b) Surface Casing

3. What is the space between the casing and the borehole wall called?

(a) Annulus (b) Cement sheath (c) Casing head (d) Running shoe

Answer

(a) Annulus

4. Why is cementing the casing important?

(a) To prevent corrosion of the casing. (b) To create a strong bond between the casing and the formation. (c) To enhance the flow of production fluids. (d) To increase the well's production rate.

Answer

(b) To create a strong bond between the casing and the formation.

5. Which of these is NOT a challenge encountered while running casing?

(a) Difficult formations (b) Pressure control (c) Casing integrity (d) Increasing wellbore diameter

Answer

(d) Increasing wellbore diameter

Running Casing Exercise:

Scenario: A well is being drilled in a shale formation. The wellbore depth is 10,000 feet. You are tasked with recommending the type and size of casing needed for each stage of the drilling and completion process.

Instructions:

  1. Identify the types of casing required for this well (conductor, surface, intermediate, production).
  2. Determine the appropriate size and grade of each type of casing, considering the geological conditions and expected pressures.
  3. Explain your rationale for each decision.

Exercice Correction

Here's a possible solution:

**1. Types of Casing:**

  • **Conductor Casing:** This will be the first string of casing to be run. It needs to provide initial stability and protect the surface environment.
  • **Surface Casing:** This casing is crucial to isolate freshwater aquifers and protect the surface environment.
  • **Intermediate Casing:** Since the well is in a shale formation, there may be challenging geological conditions. An intermediate casing may be necessary to provide additional stability and zonal isolation.
  • **Production Casing:** This will be the final string of casing used to produce hydrocarbons.

**2. Size and Grade:**

  • **Conductor Casing:** A typical size is 16 inches in diameter, but this can vary depending on the surface environment. A grade of N-80 or higher is recommended to withstand potential surface loads.
  • **Surface Casing:** The size will depend on the depth of the freshwater aquifer. A typical size could be 10 inches, with a grade of N-80 or higher.
  • **Intermediate Casing:** The size and grade will depend on the formation pressures and the specific challenges encountered. A size of 8 inches with a grade of L-80 or higher might be appropriate.
  • **Production Casing:** The size will be determined by the expected production rate and the well's overall design. A typical size could be 5.5 inches, with a grade of P-110 or higher.

**3. Rationale:**

  • **Conductor Casing:** This is the initial casing, so it needs to be strong enough to handle potential surface loads and provide stability.
  • **Surface Casing:** It needs to be strong enough to withstand the pressures of the freshwater aquifer and provide isolation.
  • **Intermediate Casing:** Shale formations can be challenging, so intermediate casing is often used to provide additional support and zonal isolation.
  • **Production Casing:** This needs to be strong enough to withstand the pressures of the reservoir and provide a safe and efficient conduit for hydrocarbon production.

**Note:** This is just a general guideline. The specific size and grade of casing will depend on the specific well design and the geological conditions. Consulting with experienced engineers and geologists is crucial to determine the appropriate casing for each well.

Books

  • "Drilling Engineering" by J.P. Brill: A comprehensive textbook covering drilling and well completion, including a dedicated section on casing design and running operations.
  • "Petroleum Engineering Handbook" by SPE: A definitive reference guide for petroleum engineers, containing extensive information on casing design, running, cementing, and testing.
  • "Well Completion Design and Operations" by W.F. Roberts: A practical guide to well completion techniques, with chapters dedicated to casing selection, running, and installation.

Articles


Online Resources

  • Society of Petroleum Engineers (SPE): The SPE website offers a wealth of technical information, training resources, and case studies on various aspects of drilling and well completion, including casing operations.
  • Schlumberger: Schlumberger's website provides a library of technical documents, videos, and case studies on casing design, running, cementing, and testing.
  • Halliburton: Halliburton, another major oilfield services company, offers online resources and information related to casing design, running, and well completion operations.

Search Tips

  • "Running Casing" + "Drilling & Well Completion": This query helps to narrow down search results to relevant content related to the process in a drilling and completion context.
  • "Casing Design" + "API Spec 5CT": This query reveals information on casing specifications, material requirements, and industry standards (API Spec 5CT is a key standard for casing).
  • "Casing Running Procedures" + "Operator Name": Use the name of a specific oil and gas operator to find relevant internal procedures or case studies related to their casing operations.

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