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Abstract In North America, refracturing existing fracked shale wells, is carried out by installing smaller liners with the already proven success of using frac plugs for zonal isolation. Post stimulation, intervention operation is carried out to remove the plugs via milling on coiled tubing. Due to restricted Internal Diameter (ID) of the smaller liner, it was critical to deploy slim hole downhole tools which is fishable but still allows higher flow rate capacities with lowest pressure drops to maximize clean out efficiency. Smaller casing/liner, smaller Coiled Tubing (CT) Outer Diameter (OD), higher wellhead pressures, higher circulating pressures, smaller OD Bottomhole Assembly/s (BHA), tougher frac plugs etc. make wellbore cleanout more challenging than a newly completed well. Under normal circumstances, a 2" OD CT in a smaller casing/liner ID, should be able to provide the desired Weight on Bit (WOB) for millout, however in this case based on modelling, it was determined that an extended reach tool would be required to achieve the objective. This paper will discuss the steps incorporated to configure slim hole BHA at higher flow rates, which includes the workover motor and the extended reach tool, to successfully remove frac plugs inside refrac liner. Several dynamometer flow tests on the motors were conducted at higher than published design flow rate and post disassembly inspections were made to ensure the motor maintained full integrity and reliability at higher flow rates. The extended reach tool vendor modified the tool for higher flow rate capacity to provide maximum traction force. This tailor-made approach eliminated the need for a diverter sub, historically used in these applications to achieve higher flow rates of ~2. 6 Barrels Per Minute (BPM). Excluding the diverter sub, assured no compromise to the motor's power delivery, or the traction force of the extended reach tool. By maintaining 2. 6 BPM, it increased annular velocities by 30% resulting in improved solid transport for efficient clean out in three wells each with ~ 16, 500 ft Measured Depth (MD). This approach has resulted in an overall time saving of 65 hours to the operator compared to previous jobs allowing to save up to 130k USD in three well pad with average wellhead pressures of 4, 000 psi inside 3-1/4" 7. 9 lb/ft liner.
Unnikrishnan et al. (Tue,) studied this question.