Table of Contents
Journal of Petroleum Engineering
Volume 2014 (2014), Article ID 126167, 8 pages
http://dx.doi.org/10.1155/2014/126167
Research Article

The Mechanism of Wellbore Weakening in Worn Casing-Cement-Formation System

1Texas A&M University, College Station, TX 77843, USA
2University of North Dakota, Grand Forks, ND 58202, USA

Received 25 February 2014; Accepted 3 June 2014; Published 24 June 2014

Academic Editor: Guillaume Galliero

Copyright © 2014 Zheng Shen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Maintaining casing integrity, in terms of downhole zonal isolations and well stability, is extremely important in oil/gas wells. Casing wear occurs not only in directional drilling, but also in vertical drilling with a slight deviation angle. In most hydrocarbon wells, deteriorated casing was reported from the onset of casing wear by the presence of friction force during the rotation of drillpipe. The friction force against the casing wall causes the reduction of casing strength. Furthermore, the rotation of drillpipe combined with corrosive drilling fluids could dramatically degrade the casing strength. We used a finite element analysis to focus on the stress evolution in worn casings. Comparison study between worn casing and perfect casing was conducted. Our study showed that the thermal load significantly increases the stress concentration of the worn casing in the wellbore. Finite element solutions indicated that the radial stress of the worn casing is not affected as much as the hoop stress. Along with the increased burst pressure or the elevated temperature, the unworn portion of the casing also suffers from severe compression stress. This work is important to broadening the understanding of well engineers through addressing the true stress profile of worn casing in cemented wellbore.