Analytical investigations of in situ stress inversion from borehole breakout geometries  

作　　者：Zizhuo Xiang Taehyun Moon Joung Oh Guangyao Si Ismet Canbulat 

机构地区：[1]School of Minerals and Energy Resources Engineering,University of New South Wales,Sydney,NSW,2052,Australia [2]HNTB Corporation,3505th Ave.,58th Floor,New York,NY10118,USA

出　　处：《Journal of Rock Mechanics and Geotechnical Engineering》2024年第7期2375-2387,共13页岩石力学与岩土工程学报（英文版）

基　　金：funded by the Australian Coal Industry’s Research Program(ACARP,Grant No.C26063).

摘　　要：This study aims to investigate the feasibility of deriving in situ horizontal stresses from the breakout width and depth using the analytical method.Twenty-three breakout data with different borehole sizes were collected and three failure criteria were studied.Based on the Kirsch equations,relatively accurate major horizontal stress(sH)estimations from known minor horizontal stress(sh)were achieved with percentage errors ranging from 0.33%to 44.08%using the breakout width.The Mogi-Coulomb failure criterion(average error:13.1%)outperformed modified Wiebols-Cook(average error:19.09%)and modified Lade(average error:18.09%)failure criteria.However,none of the tested constitutive models could yield reasonable sh predictions from known sH using the same approach due to the analytical expression of the redistributed stress and the nature of the constitutive models.In consideration of this issue,the horizontal stress ratio(sH/sh)is suggested as an alternative input,which could estimate both sH and sh with the same level of accuracy.Moreover,the estimation accuracies for both large-scale and laboratory-scale breakouts are comparable,suggesting the applicability of this approach across different breakout sizes.For breakout depth,conformal mapping and complex variable method were used to calculate the stress concentration around the breakout tip,allowing the expression of redistributed stresses using binomials composed of sH and sh.Nevertheless,analysis of the breakout depth stabilisation mechanism indicates that additional parameters are required to utilise normalised breakout depth for stress estimation compared to breakout width.These parameters are challenging to obtain,especially under field conditions,meaning utilising normalised breakout depth analytically in practical applications faces significant challenges and remains infeasible at this stage.Nonetheless,the normalised breakout depth should still be considered a critical input for any empirical and statistical stress estimation method given its significant correl

关 键 词：Borehole failure In situ stress estimation In situ horizontal stress ratio Conformal mapping Complex variable method Breakout stabilisation 

分 类 号：TU43[建筑科学—岩土工程]