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The Scientific World Journal
Volume 2013, Article ID 931034, 7 pages
http://dx.doi.org/10.1155/2013/931034
Research Article

Chemical Effect on Wellbore Instability of Nahr Umr Shale

1State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China
2Exploration & Production Research Institute, CNPC, Beijing 100011, China

Received 15 July 2013; Accepted 8 September 2013

Academic Editors: A. M. Efstathiou and A. Vorontsov

Copyright © 2013 Baohua Yu 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

Wellbore instability is one of the major problems that hamper the drilling speed in Halfaya Oilfield. Comprehensive analysis of geological and engineering data indicates that Halfaya Oilfield features fractured shale in the Nahr Umr Formation. Complex accidents such as wellbore collapse and sticking emerged frequently in this formation. Tests and theoretical analysis revealed that wellbore instability in the Halfaya Oilfield was influenced by chemical effect of fractured shale and the formation water with high ionic concentration. The influence of three types of drilling fluids on the rock mechanical properties of Nahr Umr Shale is tested, and time-dependent collapse pressure is calculated. Finally, we put forward engineering countermeasures for safety drilling in Halfaya Oilfield and point out that increasing the ionic concentration and improving the sealing capacity of the drilling fluid are the way to keep the wellbore stable.