A Mechanical Analysis of BHA Used in Casing-Window-Milling for Sidetracking

Abstract

As more and more sidetracking old wells are required in mature fields, a lot of applications in casing window milling technology, such as drilling for unconventional oil and gas, multi-lateral wells and laterals, are applied. In this paper, the mechanical properties of the BHA in different stages of window milling for sidetracking are analyzed in detail. Based on the commonly-used vertical and horizontal bending analysis, mechanical analysis models of BHA with three bits for windows milling are proposed. With these mechanical analysis models, different mechanical parameters of window milling BHA at different stages during the window operation can easily be calculated. The research achievement in this paper is helpful not only to understand the relationship between drilling parameters and drill string, stress and deformation of bits, but also to predict the side force and direction of bits and to determine the size of the drill string deformation. It can also provide references to BHA design and the selection of sidetracking operation parameters.