Critical Length Analysis for Linear Growth of Frictional Resistance of Moving Flexible Screen String in Horizontal Borehole

Aiming at the sand control problem of screen in ultra-short radius horizontal well, the influence factors of motion resistance and extension length of flexible screen are studied. Therefore, based on the theory of multi-body dynamics, a mathematical model of the downhole motion resistance of the flexible screen with spherical hinge connection was established, and the simulation model of the motion resistance of the flexible screen was constructed by ADAMS software, and the influence of multiple factors on the model of the pipe string was analyzed. The results show that the motion resistance of flexible screen increases exponentially with the increase of the total length of screen and the friction coefficient. There is a critical length with linear increase of motion resistance, and the main factors affecting the critical length are the length of screen element and the friction coefficient. Under limited thrust, increasing the length of the screen unit and reducing the downhole friction coefficient are beneficial to improve the critical length of flexible screens in downhole operations. In addition, considering the accumulation rate of downhole resistance, a local weight reduction method for flexible screen is proposed, which can not only improve the critical length, but also ensure the reliability and safety of the screen operation. This study aims to provide a theoretical basis for mastering the change law of motion resistance and extension length of flexible screen with spherical hinge connection, and provide a reference for the optimization design of flexible screen.