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Mesoscale numerical study on the evolution of borehole breakout in heterogeneous rocks
Author(s) -
Li Yingchun,
Qu Yaodong,
He Qiangyuan,
Tang Chunan
Publication year - 2020
Publication title -
international journal for numerical and analytical methods in geomechanics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.419
H-Index - 91
eISSN - 1096-9853
pISSN - 0363-9061
DOI - 10.1002/nag.3058
Subject(s) - borehole , geology , breakout , geotechnical engineering , mesoscale meteorology , anisotropy , hydrostatic equilibrium , stress (linguistics) , stress field , rock mechanics , finite element method , structural engineering , engineering , linguistics , philosophy , physics , finance , climatology , quantum mechanics , economics
Summary Inherent heterogeneity of a rock strongly affects its mechanical behavior. We numerically study the mechanisms governing the initiation, propagation, and ultimate pattern of borehole breakouts in heterogeneous rocks. A two‐dimensional finite element model incorporating material heterogeneity is established to systematically examine the effects of several key factors on borehole failure, including borehole diameter, far‐field stress, and rock heterogeneity. The inherent heterogeneity of a rock is explicitly characterized by prescribing the rock mechanical properties of mesoscale elements statistically obeying the Weibull distribution. Elastic damage mechanics is used to represent the constitutive law of the mesoscale element. We find that borehole diameter reduction remarkably changes the crack failure from tensile to shear and elevates the critical hydrostatic pressure. Far‐field stress anisotropy strongly affects the shape of the borehole breakout. Rock heterogeneity dictates the location of the preferred crack under the hydrostatic stress, which leads to local stress concentration, and determines the types of breakouts around the borehole. Our findings facilitate in‐depth understanding of the classic borehole stability problems in heterogeneous rocks.