The increasing lateral lengths of wellbore and additional composite frac plugs (CFP) per well has created a need for a more efficient and aggressive post frac millout of plugs using coiled tubing (CT). Economic post job analysis has shown some advantages and drawbacks of using larger diameter coiled tubing and more robust tools, all while developing a better understanding of the impact to the operation. Several complexities exists downhole that are not well understood. Attempts to comprehend downhole conditions are limited by past experiences, pre-job software modeling, and post-job matching through the uses of surface parameter but not actual downhole data.
Monitoring downhole forces applied when performing post frac milling operations, through the use of a memory sub, gives a better understanding of forces that are actually transmitted from the tools to the CFP in the actual wellbore environment. Thru tubing tools selection is based on actual downhole data which translates to an overall increase in efficiency of the operation.
A closer look at the actual downhole parameters, when performing operations with larger diameter CT and extend reach tools, lead to findings that the weight on bit (WOB) applied to a plug in the lateral of a well can be as high as 15,000 lbf. This amount of force far exceeds what is applied at surface and what conventional software modeling shows. This also greatly surpasses the recommended WOB while drilling the CFP. Applying substantial downward force to the CFP results in movement of the plug prior to being completely milled up, which causes significant operational issues. These same forces that cause the aforementioned issues are necessary to aid in having consistent mill times throughout the operation, enough WOB to get CT to reach measure depth (MD), and produce an operation that is completed in a timely and economically sound manner.