ÿþ<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <title>Analysis of stuck pipe in deviated boreholes Bernt S. Aadnøya,*, Kenneth Larsenb, Per C. Bergn</title> <meta http-equiv="content-type" content="text/html;charset=windows-1251"> <link rel="stylesheet" type="text/css" href="../master_style.css"> <meta name="ROBOTS" content="noindex, nofollow"> </head> <body> <h2 align="center"><b>Analysis of stuck pipe in deviated boreholes Bernt S. Aadnøya, Kenneth Larsenb, Per C. Berg</b></h2> <h4 align="center">S.B. Smithsona, F. Wenzelb, Y.V. Ganchina, I.B. Morozov</h4> <HR> <p align="center"color="mediumstateblue"> <br><h3>Abstract</h3> <div align="justify" style="margin-left: 20px; margin-right: 20px; font-weight: normal"; ><font size=4> <img src="../a.gif" width=20 height=1><p>&nbsp &nbsp &nbsp <div align="justify" style="margin-left: 20px; margin-right: 20px; font-weight: normal"; ><font size=4> <img src="../a.gif" width=20 height=1><p>&nbsp &nbsp &nbsp 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.</p></div> <br><h3>1. Introduction<br><h3> <div align="justify" style="margin-left: 20px; margin-right: 20px; font-weight: normal"; ><font size=4> <p>&nbsp &nbsp &nbspThe complexity of the wells has increased significantly in later years. Their reach has more than doubled, and high-inclination and fully 3-D well paths are common. However, statistics shows that sidetracking the boreholes due to stuck pipe has also shown a significant increase and is presently a high-cost factor. The margins between success and failure are now much smaller. When a drill string gets stuck during drilling, operational procedures are applied to release the drill. string. These procedures include working the drill string up or down, attempting to rotate the string and pumping mud through the drill bit to aid pipe release. One may also place different fluids around the stick area and use a drilling jar. Although sound and justified, today s practices lack engineering calculations. Current stuck point formulae neglect well friction and deviation and are, therefore, valid for vertical wells only. A free-point indicator can be run to determine the stuck point, but this operation takes considerable time. As a result of the limitation with the current operational practices, a larger study was initiated to understand the stuck pipe situation better and to develop improved procedures. A mechanistic approach was chosen. The following elements were analyzed: (1) the forces developed during differential sticking; (2) pipe strength under combined loads: tension, torque and pressure; (3) effects of buoyancy under various conditions like equal or different mud densities in drill pipe and annulus; and (4) wellbore friction as related to torque and drag.<br> </body> </html><br><br>