To ensure high efficiency of well workover using coiled tubing rigs it is important to correctly choose process fluids and modes of injection. One of the findings of the hydraulic analysis of the circulation system of the coiled tubing rig is that due to the small run-in clearance of the coiled tubing considerable hydraulic pressure losses occur. Coiled tubing with the external diameter of 38.1÷50.8 mm are most commonly used in Russia. Furthermore, they are practically unaffected by the well depth which is due to the design features of the coiled tubing rig which provides for the pumping of the process fluids through the whole CT string including the CT that is on the reel. Additional hydraulic resistances caused by the curvature of the reeled CT are small due to the high ratio between the diameters of the spool and the tubing, hence, they can be ignored.

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