Session on Cement Evaluation: The Basics and Beyond

Introduction

• Hosted by PIO Petro Arab Oil & Gas Academy and SBE Egypt Section
• Moderator: Shahad Behjat, 3rd-year Petroleum Engineering student at KNU in Kurdistan, Iraq
• Four-part webinar series by Mr. Kirk Harris on Cement Evaluation: The Basics and Beyond
• Mr. Harris's background:
  • Graduated from Purdue University with a B.S. in Civil Engineering
  • Career at Halliburton, Occidental Petroleum, Talisman Energy, Repsol, and currently Technical Advisor at ThroughBond LLC
  • Extensive regional experience in cementing operations worldwide

Session Overview

• Week 1: Cement Bond Log (CBL) Basics
• Week 2: Ultrasonic Log
• Week 3: Advanced Interpretation (Log Interpretation)
• Week 4: Shallow Casings and Shoe Tests

Cement Bond Log (CBL)

• CBL Tool Components
  • Transmitter
  • Receivers (3ft and 5ft)
• CBL Interpretation Method called the Five C’s:
  • Construct: Build an understanding of the well construction
  • Compare: Review and compare sections of the log
  • Correlate: Examine changes and correlate with well data
  • Consider: Account for factors impacting the reading
  • Conclude: Arrive at a final interpretation
• Publications Recommended for Further Reading:
  • API Best Practices for Cement Sheath Evaluation
  • Schlumberger's literature on Bond Log Interpretation

Importance of Cement Bond Log

• Determines the success/quality of a cement job
• Used in well abandonment to ensure well integrity
• Controversial due to difficulty in interpretation vs. necessity
• Practical Insights:
  • Trust the cement job data before the log data
  • Importance of observing log patterns

Common Observations and Terms

• Straight Lines: Often indicate free pipe/no cement
• Squiggly Lines: Indicate formation signals
• Casing Ring Effect: Observed at casing collars
• Pressure Pass: Changes in amplitude upon applying pressure can provide useful info

Key Points in CBL Interpretation

• Observe the wellbore isolation
  • CCL (Casing Collar Locator)
  • Gamma Ray Log
  • Transit Time Curve
  • Amplitude Curve
  • Variable Density Log (VDL)
• Identify top of cement, changes in amplitude, and formation signal patterns

Practical Examples and Case Studies

• Free Pipe: Loud signals, straight lines, strong chevron patterns
• Microannulus: Straight lines but dampened collars, presence of formation signals
• Channeling: Straight lines with partial formation signals; commonly observed in poor bonding situations
• Perfect Cement: No straight lines, consistent signals indicating good bond
• Effects of Well Factors: Lightweight cement, new casing, pressure testing—all impacting log readings
• Practical Case Issue: Example of injection well where bond log revealed issues otherwise undetected

Summary & Lessons

• Cement logs are essential but require practice and expert observation for accurate interpretation.
• Discussed potential for machine learning and AI to aid log interpretation.
• Emphasized the importance of constructing wellbore data and collaboration with geologists.

Q&A Highlights

• Cementing with Losses: Best practice to assess and address losses before proceeding to avoid poor cement jobs.
• Amplitude Misinterpretation: Discussed common scenarios where amplitude may give misleading results.
• Channeling vs. Poor Bonding: Interpretation nuances between these conditions.
• Automation of Log Interpretation: Potential for machine learning with expert knowledge input.