A new downhole machining system has been developed for lightweight intervention applications to remove wellbore obstructions and stuck valves, combining the precision of real-time bit position measurement with the power of push-pull forces up to 40,000 lbf. This tool builds on existing hardware from proven milling and shifting services, with added software features for advanced automation and control. This paper describes the new machining system and benefits for the operator to enable a reliable and robust contingency machining service.

Conventional wireline milling tools use a tractor tool for weight-on-bit and torque reaction. These tractorbased milling systems can be efficient for removing obstructions over a long interval, but they are not ideal for milling hard metal targets. For example, a nipple milling operation might require many hours to mill, during which time the operator has no indication that the milling operation is progressing as planned since the tractor does not provide any measurement of milling progress. The new machining system provides the operator with a real-time measurement of milling progress with resolution down to 1/100-in. to quickly diagnose and correct any problems due to bit damage, engagement with the target, or cuttings accumulation. For known targets of multiple materials or interrupted geometry, or for bits with staged cutting features, the direct measurement of bit position enables automatic machining programs that can autonomously execute a predefined sequence of cutting parameters (weight, speed, and torque) that change with measured bit position. The machining progress and quality indicators are displayed in real time at surface using a graphic interface showing the machining target and current bit position.

The machining tool uses the same anchor and linear actuator modules from wireline shifting service tools, combined with the same rotary motor and gearing modules from wireline milling service tools. Torque from the bit is transferred across the linear actuator module using a sleeve that is keyed above and below the piston. Both the linear actuator hydraulic motor and the rotary motor are equipped with rotor position and torque feedback and powered by a downhole inverter for maximum power efficiency, precise control of hydraulic pressure and bit position, and reverse operation for stall prevention and recovery.

Test data are shared in this paper to compare the performance of the new machining tool with a high-performing tractor-based milling service tool. Examples are given for both isolation valve machining and nipple machining.