Cementation of Liners: Precision in Challenging Well Conditions

 

Introduction

"What makes liner cementation different from full-string cementing?" The cementation of liners presents unique challenges and opportunities, especially in complex wells such as deviated or horizontal trajectories. This article explores the critical procedures, challenges, and real-world applications of liner cementing.

What is Liner Cementation?

Liner cementation involves placing cement around a casing section that does not extend to the surface, referred to as a liner. The liner is typically hung from the lower end of the previous casing string using a liner hanger.

Key Differences from Full-String Cementing:

• Length: Liners are shorter and do not reach the surface.
• Hanging Mechanism: Requires a liner hanger system for support.
• Applications: Often used in deep wells, sidetracks, and extensions.

Procedures in Liner Cementation

1. Planning and Design

• Data Collection: Gather formation data, pressures, and well trajectory.
• Liner Selection: Choose the appropriate length, diameter, and materials.
• Cement Slurry Design: Optimize for zonal isolation and operational conditions.

2. Installation of the Liner

• Run-In-Hole: Lower the liner into position using a running tool.
• Set the Hanger: Deploy the liner hanger to suspend the liner.

3. Cementing Operations

• Spacer and Cement Slurry Pumping:
  • Pump spacer fluid to displace mud.
  • Follow with cement slurry, ensuring uniform placement.
• Reverse Circulation: Commonly used to minimize pressure on weak formations.
• Wiper Plug: Use to separate cement slurry and displacement fluid.

Challenges in Liner Cementation

1. Deviated and Horizontal Wells

• Challenge: Maintaining cement placement uniformity due to gravity.
• Solution:
  • Use centralizers to improve cement placement.
  • Adjust fluid rheology for effective displacement.

2. Liner Hanger Failure

• Challenge: Improper setting of the hanger can compromise the liner's stability.
• Solution: Perform hanger integrity tests before cementing.

3. Formation Damage Risks

• Challenge: Over-pressurizing weak formations during cementing.
• Solution: Opt for reverse circulation techniques to reduce pressure.

Case Study: Liner Cementing in a Deviated Well

Scenario:

A 1,500 ft liner needed cementation in a deviated offshore well with a 45° inclination.

Challenges Faced:

1. Uneven cement distribution due to deviation.
2. High risk of mud channeling.

Solutions Applied:

• Spacer Design: High-viscosity spacers were used for effective mud removal.
• Centralizer Placement: Centralizers were spaced optimally to keep the liner centered.
• Reverse Circulation: Reduced the risk of over-pressurizing the formation.

Outcome:

The cementing job successfully achieved zonal isolation, supporting long-term well integrity.

Best Practices in Liner Cementation

1. Thorough Pre-Job Planning:
   • Model cement flow and displacement profiles.
2. Use Advanced Tools:
   • Employ centralizers, scratchers, and wiper plugs.
3. Real-Time Monitoring:
   • Monitor pressures and returns to adjust pumping rates dynamically.

Conclusion

Liner cementation is a sophisticated process requiring meticulous planning and execution. With tailored techniques and real-time adaptability, it is possible to overcome challenges and ensure a robust cementing job.