Investigation of failure region around the wellbore based on the extended Mogi-Coulomb criterion for rock matrix

ABSTRACT

In order to investigate the failure region around wellbore under a given mud pressure, three different strength criteria are fit to triaxial experimental data, then the strength criterion with the smallest fitting error is selected to analyse wellbore stability. Based on the investigate of rock strength criteria, a prediction model for the shear failure region around borehole is established. The influence of wellbore trajectory on the shape and position of shear failure region around wellbore, and collapse pressure variation at wellbore wall is analysed. Results indicated that, the area of shear collapse around the well predicted by Mohr-Coulomb criterion (MC) is elliptic, while the same results predicted by extended Mogi-Coulomb criterion (EMG-C) is approximately quadrilateral. The intermediate main stress decreases the collapse pressure and its anisotropy at the wellbore wall, but increases the failure region around the wellbore. The EMG-C takes into account the effect of intermediate principal stress and the nonlinear failure characteristics of rocks in high stress environment, and the prediction position of the shear collapse region around the borehole is quite different from the shape predicted by MC criterion.

KEYWORDS:

• Principal stress space
• intensity criteria
• borehole collapse
• failure region around wellbore
• extended MG-C criterion

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by the National Natural Science Foundation of China [Grant No. 51474185 and 51774246]; the National Key Basic Research and Development Program, (973 Program) China [Grant No. 2013CB228003]; Sichuan academic and technical leaders Training Fund [Grant (2016)183]; Science and Technology Project of CNPC Chuanqing Drlling Engineering Company Limited [Grant No. CQ2019B-8-1-3].