An unsuccessful cement job left a well in the Sultanate of Oman with 4,000 meters of undesired cement plug, putting customer investment at risk. The cement obstruction required an extended intervention operation to complete the well for a planned hydraulic fracturing treatment. Concerns were raised about the potential operation duration and the number of motors and mills to be deployed. Preliminary estimates indicated that 90 days would be required to reach TD.

Real-Time Hybrid Coiled Tubing (RTHCT) with an unlimited power supply was proposed to provide downhole insight through real-time weight on bit and torque readings to optimize the motor performance and minimize the number of runs and motors. Planning for such an operation was crucial, including having all Bottom Hole Assembly (BHA) components available to cover all planned runs and expected contingencies such as stuck pipe. The first run was planned with a junk mill to help mill the top plug and cement, followed by a bear claw mill to help improve the penetration rate, and then a standard polycrystalline diamond compact bit for cement milling. A variety of different size taper mills were also made available to clear any required restrictions.

The cement milling operation was successfully completed in four (4) runs, averaging four (4) days per run. The RTHCT helped drive the decision-making process on location by pulling out of hole only when motor torque was insufficient. 1,460 m and 1,550 m were achieved on the first and second runs utilizing the three planned mills. The downhole sensors in the BHA provided real-time insight to optimize the motor performance, evaluate the motor life, and maximize results on every run. The job was completed without a single motor stall and approximately seven (7) times higher overall Rate of Penetration (ROP) than conventional CT milling operations. After successful milling, a high-pressure rotating jet nozzle was run to help ensure no cement sheath remained that could jeopardize future interventions. Research indicates that 4,000 m of cement milling is greater than any other CT operation has achieved globally in a single well.

The RTHCT combined intervention and diagnostic capabilities to provide real-time downhole insight for a precise decision-making process to achieve the operation's success. The operator saved a high investment well along with the rig costs that would normally be associated with such an operation.

This paper discusses the collaborative efforts from planning and design to executing this successful operation, including the contingency plans that were crucial in reducing the time to plan resources during unexpected events.

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