System and methodology for determining appropriate rate of penetration in downhole applications

A method, comprising:

• positioning a downhole well tool of a well system on coiled tubing to form a coiled tubing string;
• obtaining sensor data as the downhole well tool is moved along a wellbore by the coiled tubing, wherein the sensor data comprises a load cell measurement acting on the coiled tubing string;
• using the sensor data to determine a coefficient of friction (COF) value based on friction acting on the coiled tubing string;
• updating the COF value based on the sensor data to obtain updated COF values when the downhole well tool is moved to different positions in the wellbore;
• and
• controlling an injector head of the well system to automatically adjust a hanging weight of the coiled tubing based at least in part on the updated COF value to achieve a desired rate of penetration (ROP).

A system, comprising:

• a coiled tubing string having a milling tool deployed downhole in a wellbore of a well system via coiled tubing;
• a sensor system having one or more surface sensors and one or more downhole sensors, the one or more downhole sensors being mounted on the coiled tubing string;
• and
• a processing system that receives sensor data from the sensor system in substantially real time at a plurality of locations along the wellbore, determines a coefficient of friction (COF) value acting on the coiled tubing string at each of the plurality of locations along the wellbore based at least in part on the sensor data, and automatically controls an injector head of the well system to optimize a rate of penetration (ROP) during a milling operation based at least in part on the COF values determined at the plurality of locations along the wellbore.