WOB Prediction for CT Casing Window Milling

The WOB during window milling in coil tubing(CT) casing is hardly controlled,so motors might be damaged,and undesirable quality of the window might be caused.With the window milling of whipstock as object,the "vertical and horizontal bending method" was used for programming of computer software to calculate forces and deformation of drilling assemblies with specific structures for windowing in coil tubing in the one-dimensional wellbore.With consideration to cutting conditions similar with those encountered in field,three limiting conditions have been clarified,namely,proper functioning of the motor,drilling in accordance with pre-determined trajectory and generation of high-quality window,to predict range of acceptable WOBs during window milling.Research results show that proper prediction of WOB during window milling in coil tubing may be favorable for protection of drilling tools and generation of high-quality window.Such results may provide necessary guidance for on-site application.Since the motor may stall at the stage of initial window milling,minor drilling pressures shall be deployed.