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Type: Conference paper
Title: Effect of grain bonding on the stability of a borehole drilled though low cemented formations
Author: Hashemi, S.
Melkoumian, N.
Xu, C.
Citation: Proceedings: the 7th Australasian Congress on Applied Mechanics (ACAM 7), 9-12 December 2012, Adelaide: pp.884-894
Publisher: Engineers Australia
Publisher Place: CDROM / DVDROM
Issue Date: 2012
ISBN: 9781922107619
Conference Name: Australasian Congress on Applied Mechanics (7th : 2012 : Adelaide, S.A.)
Statement of
S. Saeid Hashemi, Noune Melkoumian and Chaoshui Xu
Abstract: Achieving an in-depth understanding of the behaviour of low cemented formations such as running sands around a cylindrical borehole is of significant importance in identifying stability problems, designing adequate borehole supports and choosing an efficient drilling method. This paper presents numerical investigations on failure modes of unsupported vertical cylindrical boreholes drilled through weak formations, i.e. low cemented sands where the movement of individual grains is not restricted by sufficient cementation. Distinct element method (DEM) was used for this study. The method enables to simulate sand grains and control normal and shear bonding between them. To simulate actual condition surrounding a borehole at a depth of 80m, a 2m x 2m x 2m cube made up of spherical particles with diameters ranging from 5mm to 70mm was constructed and analysed in the DEM code, PFC3D. The results showed that stress concentration developed in the ground due to the presence of a borehole leads to the formation of a damage zone around that borehole. When there is not sufficient bonding between the sand grains, the interaction between them results in their movement towards the borehole and the eventual collapse of the borehole wall. The effect of fluid flow on stability of boreholes has been studied as well. The cementation between sand grains is mainly caused by the presence of clay particles in the formation. The bonding strength between sand grains is an intrinsic or micro property of the bonding material and is very difficult to measure in laboratory conditions. The results obtained from current research will help to evaluate the effect of particle bonding on the mechanical behaviour of low cemented formations and develop methods to assess borehole stability during and after drilling through such formations.
Keywords: Borehole stability
distinct element method
particle bonding
unconsolidated formations
Rights: Copyright status unknown
Published version:;dn=129091780891685;res=IELENG
Appears in Collections:Aurora harvest
Civil and Environmental Engineering publications

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