Selection and Application of Ultra-Deep Extended Reach Well Trajectory Design Scheme Based on Entropy Weight Method

During the drilling and completion of ultra-deep Extended-Reach Well(ERW), technical challenges such as high risk of lost circulation, difficulties in well trajectory control, poor hole cleaning, narrow drilling fluid safety density window, and high friction and torque are encountered. The trajectory design of ultra-deep ERW is a key element for it’s safe and efficient drilling which needs a comprehensive analysis and evaluation. In this paper, a model for evaluating the trajectory design scheme of ultra-deep ERW was established based on the entropy weight method, in which the weights are calculated and the schemes are scored by making comprehensive analysis of 25 evaluation indexes of mechanical, hydraulic and long open hole wellbore stability, so that the 3 trajectories of slant profile, catenary profile, pseudo-catenary profile for EP21-X-A1H ultra-deep ERW are quantitatively evaluated and results are elaborated. Pseudo-catenary profile is the best. The well site is carried out in strict accordance with the proposed pseudo-catenary profile trajectory, with a target depth of 9508 m and a step-out ratio of 4.43, making it the deepest well in China's offshore region by now, the trajectories between actual and design are high degree of consistency and rank excellent well scheme quality. The EP21-X-A1H ultra-deep ERW case has been successfully applied the effects of this model. This research not only provides a guidance method for the selection of trajectory design scheme of ERW, but also a technical reference for the subsequent drilling technology optimization and risk evaluation of ERW.