Abstract
This paper presents a systematic workflow/methodology developed to evaluate the milling operations using coiled tubing to remove frac plugs in a well with deformed liner, post hydraulic fracturing. This paper also presents the challenges encountered during intervention and steps on how they were mitigated.
The well was completed by hydraulic fracturing of five stages, each separated by a frac plug. Post stimulation, coiled tubing was mobilized to mill the plugs and provide a full bore to begin production. After spending substantial time while attempting to mill in the initial run, decision was made to POOH and inspect the BHA. It was observed that the mill had significant metal loss on the outer periphery with no damage to the mill face, which thereby concluded the presence of liner damage. A strategy was developed on how to remediate this challenge. Multiple coiled tubing diagnostic runs were performed with real-time coiled tubing capabilities, which included cleanout, camera and caliper runs.
Results of each coiled tubing run performed was carefully evaluated to estimate the extent of liner damage. The caliper and video camera runs were important to determine the new reduced ID of the liner. An initial milling attempt with a 3.33" OD mill was performed, which was the smallest size based on the plug manufacturers recommendation. However due to the specific nature of liner damage it could not pass through the restriction. After further discussions, a calculated risk was taken to run with a 3.125" OD mill, which was significantly smaller than the manufacturer's recommendation, and posed an inherent threat of milling through the core of the plug, while leaving the slips intact. This however did not happen, and all four plugs were successfully milled out from the liner, allowing full bore access and well to be flowed back.
This paper will act as a guideline on how to design and execute an intervention operation in deformed liners.
