First Time Coiled Tubing Milling in 7-in. Monobore Gas Well Using Downhole Real-Time Measurements
Authors: Tapia W. R. , Erkol Z. , Ramondenc P. , Houdaidon M. , Shaaban A. , Trummer S. 
Published: March 2018

One of the biggest sources of dry gas in the world is located in the Middle East. Every project in this field faces challenges that require good-quality downhole data to be properly addressed. In the present case, the risks involved when milling inside a 7-in. monobore completion with 2 3/8-in. coiled tubing (CT) in gas conditions motivated the use of a state-of-the-art bottomhole assembly capable of providing real-time downhole parameters to operate the mill both safely and efficiently.

The project, which included an extensive integration between the CT and downhole tools providers, consisted of various innovative stages. First, a stimulation vessel was used to deliver enough pumping capacity to inject the fiber optics carrier into the CT pipe located on the rig. Then, a customized surface acquisition system was implemented to comply with strict zoning requirements, and protocols and hardware were designed for communication between the software of all parties to transmit downhole and surface data in real time. Finally, a thorough analysis was conducted to identify the safest method to deploy and run the milling tools to achieve the job objective.

This successful milling operation in 7-in. monobore completion and gas conditions was the result of several achievements made throughout the project. The real-time telemetry system served rugged downhole tools, which were being used under these conditions for the first time. They provided downhole torque, pressure (both inside and outside of the milling tool), depth control variables, and weight on bit to the CT control cabin, where the CT operator and milling tool specialist effectively interpreted the data and took actions to mill 100 ft of cement and a drillable plug in three runs. The critical operation to inject the fiber optic carrier in the 2 3/8-in. CT pipe required incorporating extra measurement equipment such as flowmeters and pressure gauges in the system to closely check pumping parameters, which will now be utilized as a standard for other such interventions worldwide. Finally, the design of the communication interface between the software of the different companies proved to be effective at compiling all the critical parameters and became a benchmark for future operations.

Even though well conditions changed during the operation, the job was executed safely based on a detailed decision tree that incorporated several contingencies. Each action was reviewed by all parties based mainly on the downhole data recorded, which allowed getting the best out of the milling bottomhole assembly and the expertise incorporated in the project.

This work shares a vast amount of information collected during the design and execution of the project. The significant effort performed by all the parties to integrate their equipment and technology are detailed within the context of the job's objectives and can be used as a reference by other locations. Contingency plans are also detailed, as well as safety measures and lessons learned.