Analysis of stuck pipe in deviated boreholes

Abstract

This paper presents new equations to determine the depth to the stuck point in deviated wellbores based on pulling tests and torsion tests. In addition, methods to free a stuck pipe are given. In particular, it is shown that bends in the wellbore lead to more friction that, with the new equations, results in a deeper stuck point in a deviated well compared to a similar vertical well. Analytical equations are derived to compute forces in the drill string from top to bottom, including models for wellbore friction and pipe strength. Knowing all the forces involved in a stuck-pipe case, analysis is presented to determine the action that has the largest impact to free the pipe. One of the main conclusions is that the most important element to free the string is to keep the bottom-hole pressure as low as possible. The paper presents three methods to free the pipe, which where developed from the analysis: (1) maximum mechanical force method, (2) minimum density method and (3) maximum buoyancy method. A detailed field case from the Yme field in the North Sea will demonstrate these methods and show the effect on the stuck point using each method. It is believed that introducing a more analytical approach to stuck pipe problems will lead to more efficient drilling and improved well economy.