Cementing Horizontal and High-Angle Sections: Challenges and Best Practices

 

Introduction

"Why is cementing in horizontal wells more complex?" Cementing in horizontal and high-angle well sections presents unique challenges compared to vertical wells. The deviation from the vertical introduces issues with fluid flow, cement placement, and pressure management, which require specialized techniques and tools to ensure well integrity and zonal isolation. Understanding these challenges and best practices is crucial for achieving successful cement jobs in these demanding wellbore configurations.

Challenges in Cementing Deviated and Horizontal Wells

1. Fluid Flow and Cement Placement

In horizontal and high-angle wells, gravity does not work in the same way as in vertical wells. Cement slurry tends to move upward rather than filling the annular space between the casing and the formation. This can result in poor cement bonding in the lower sections, leaving gas or fluid migration paths that compromise well integrity.

• Challenge: Cement does not flow evenly in the wellbore, especially in horizontal sections.
• Key Strategy: Use of centralizers to help push the cement into the lower sections and ensure uniform distribution.

2. Risk of Cement Channeling

Horizontal sections are more prone to cement channeling, which occurs when the cement slurry forms channels or voids within the annular space. This often happens due to insufficient displacement or improper slurry design. As a result, the casing may not be adequately isolated from the formation, leading to gas migration and pressure control problems.

• Challenge: Cement channeling can significantly reduce the effectiveness of the cement job.
• Key Strategy: Use of spacers and washes to ensure proper displacement and reduce the risk of channeling.

3. Pressure Management

In deviated wells, the hydrostatic pressure may not be uniformly distributed due to the well's inclination, making it difficult to manage cement displacement. If pressures aren't balanced properly, the cement slurry can fail to cover the annular space fully, leaving weak spots that can lead to wellbore instability.

• Challenge: Maintaining uniform pressure in a high-angle or horizontal wellbore.
• Key Strategy: Careful management of mud weight, cement pumping rates, and pressure during cementing operations.

4. Hole Cleaning Issues

In horizontal and high-angle wells, the risk of poor hole cleaning increases due to the limited ability of drilling fluids to lift cuttings out of the wellbore effectively. The presence of debris can interfere with cement placement and bonding, leading to incomplete isolation.

• Challenge: Inadequate hole cleaning can prevent proper cement bonding.
• Key Strategy: Ensure that the wellbore is thoroughly cleaned before cementing by using appropriate circulation techniques and fluid additives.

Best Practices for Effective Cement Placement in Horizontal and High-Angle Wells

1. Centralizer and Scratchers Usage

Centralizers are crucial in horizontal and deviated wells to ensure that the casing is kept in the center of the wellbore, which facilitates even cement placement. Scratchers can be used to roughen the casing surface, improving cement bonding to the casing and reducing the likelihood of channeling.

• Best Practice: Use multiple centralizers throughout the wellbore, especially in the horizontal sections, to prevent poor cement placement.
• Best Practice: Employ scratchers where needed to enhance bonding between the casing and cement.

2. Optimal Cement Slurry Design

The design of the cement slurry is critical in deviated and horizontal wells. Slurry rheology should be tailored to ensure good flow properties and prevent settling of heavier particles. The slurry must have the right density and viscosity to achieve proper displacement while maintaining a uniform bond to the casing.

• Best Practice: Design a slurry with a stable rheology that ensures uniform distribution and prevents premature setting in the horizontal section.
• Best Practice: Use retarders and accelerators as needed to adjust thickening time and improve displacement efficiency.

3. Displacement Efficiency

Proper displacement of drilling mud with cement is vital to achieving a good cement bond in horizontal wells. A poor displacement job can leave pockets of mud in the wellbore, which will result in inadequate bonding of the cement and increase the risk of migration of fluids or gas.

• Best Practice: Use high-quality spacer fluids to effectively displace mud from the annulus and maximize cement bonding.
• Best Practice: Calculate and monitor displacement efficiency throughout the cementing process.

4. Use of Washes and Spacers

Washes and spacers are essential in horizontal and deviated wells to ensure that drilling fluid is effectively displaced and to improve cement bond integrity. Washes help remove any remaining mud or debris, and spacers aid in creating a barrier between the mud and the cement.

• Best Practice: Select spacer fluids with the right viscosity to prevent contamination and ensure smooth displacement.
• Best Practice: Use a wash before cementing to clean the wellbore and ensure a high-quality cement job.

5. Real-Time Monitoring and Evaluation

Cementing operations should be continuously monitored using real-time data collection tools like cement bond logs (CBL) and variable density logs (VDL). These tools provide insight into the quality of the cement bond and help identify any weak spots or areas that require remedial cementing.

• Best Practice: Use cement evaluation tools to assess the cement bond quality and integrity after cement placement.
• Best Practice: Perform a cement bond log (CBL) after the cement job to ensure adequate zonal isolation.

Conclusion

Cementing in horizontal and high-angle sections presents several challenges, including poor fluid flow, cement channeling, and pressure management. However, by adopting best practices such as using centralizers, designing optimal slurry formulas, improving displacement efficiency, and monitoring cementing operations in real time, these challenges can be mitigated. Successful cementing in deviated and horizontal wells ensures well integrity, zonal isolation, and long-term production stability.