CTD milling is a specialized intervention technique used in oil and gas wells to remove obstructions, clean out debris, or mill through stuck objects such as scale, cement, or metal components. A CTD milling servicing test is conducted to evaluate the performance and reliability of the milling operation before deploying it in a live well environment.
Objectives of a CTD Milling Servicing Test
- Validate Equipment Performance – Ensuring that the coiled tubing unit, downhole motor, and milling bit function correctly under simulated conditions.
- Assess Milling Efficiency – Measuring the ability of the milling tool to cut through specific materials and produce manageable cuttings.
- Verify Fluid Circulation – Testing the fluid system to ensure proper cooling, lubrication, and debris removal.
- Check Tool String Integrity – Ensuring that all downhole components (motors, jars, and mills) can withstand the expected loads and torque.
- Simulate Well Conditions – Running tests under conditions similar to the target well, including pressure, temperature, and fluid properties.
Typical Steps in a CTD Milling Servicing Test:
- Equipment Setup & Inspection:
Verify coiled tubing integrity and fatigue life.
Check motor performance and torque output.
Inspect milling bit for wear and material compatibility. - Surface Milling Test:
Conduct milling on a test block (e.g., steel, cement) to analyze penetration rate and debris size.
Monitor tool vibration and stability. - Circulation & Flow Rate Testing:
Pump fluid through the coiled tubing to check flow rate and hole-cleaning efficiency.
Evaluate hydraulic horsepower and downhole pressure behavior. - Torque & Weight-on-Bit Analysis:
Adjust weight-on-bit (WOB) and rotation speed to optimize milling performance.
Measure torque response to avoid excessive stress on the toolstring. - Real-Time Monitoring & Data Logging:
Collect downhole sensor data (if available) to monitor vibrations, temperature, and pressure.
Adjust operational parameters based on test results. - Post-Test Inspection & Analysis:
Retrieve and inspect the tool string for wear and damage.
Evaluate the effectiveness of the milling operation based on debris analysis.
Determine necessary adjustments for field deployment.
Benefits of Conducting a CTD Milling Servicing Test:
Reduces operational risks and potential downhole failures.
Improves efficiency by optimizing milling parameters before deployment.
Enhances tool life and reduces non-productive time (NPT).
Ensures compliance with well control and safety standards.