Experimental study on borehole size effect and prediction of breakout initiation stress

Published on Jun 1, 2021in International Journal of Rock Mechanics and Mining Sciences7.135
· DOI :10.1016/J.IJRMMS.2021.104762
H. Lin3
Estimated H-index: 3
(UNSW: University of New South Wales),
Joung Oh16
Estimated H-index: 16
(UNSW: University of New South Wales)
+ 3 AuthorsStuart D.C. Walsh24
Estimated H-index: 24
(Monash University)
Source
Abstract
Abstract Borehole breakout initiation stress is critical for mining and geotechnical engineering as it indicates horizontal stress magnitudes and rock quality in a specific layer. This stress can be significantly intensified under laboratory conditions where the borehole size is small, although the specimen sizes in previous studies varied. This may result in inaccurate experimental results as the sample itself is affected by the scale effect. In this paper, two series of normal compression tests (constant borehole–specimen ratio and constant specimen size) were conducted on various borehole radii (6 mm–12.5 mm) to study the influence of specimen size as well as borehole size on breakout initiation stress. Experimental results revealed that specimen size does not have an obvious influence on the breakout initiation stress when specimen to hole ratio is over 10, suggesting that data collected from previous studies in the literature are also valid and can be used for future breakout analysis. A comparative analysis of the stress averaging concept, failure criteria considering pressure-dependency and an empirical model was conducted to predict breakout initiation stress. Results showed that the stress averaging concept was not reliable for experimental data, whereas the linear fracture initiation criterion produced the most accurate results, although its parameters are dubious and difficult to obtain. An empirical relationship, derived from literature data under normal compression tests, also showed promising results in estimating breakout initiation stress. Due to its simplicity and reliability, it may be used in future studies with more validation.
References52
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Last. Panos Papanastasiou (UCY: University of Cyprus)H-Index: 24
view all 3 authors...
Abstract A computational micromechanical analysis based on zero thickness interface elements for modelling solid prediction in hydrocarbon reservoir sandstones is presented. The model is capable of modelling localization of deformation, disintegration and cracking of cemented rock formation that leads to initiation and continuous sand production during hydrocarbon production and reservoir depletion. Using only few physical parameters, the model is calibrated at the macroscale by reproducing the ...
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#1H. Lin (UNSW: University of New South Wales)H-Index: 3
#2Joung Oh (UNSW: University of New South Wales)H-Index: 16
Last. T.R. Stacey (University of the Witwatersrand)H-Index: 9
view all 4 authors...
Borehole breakout is a natural phenomenon in boreholes drilled in rock due to the induced stress concentration. Many researchers have attempted to correlate this phenomenon with in situ stress magnitudes. In this paper, a series of true triaxial tests on sandstone blocks (120 × 120 × 120 mm3) with different diameter pre-drilled holes have been carried out. Results confirmed that breakout geometries (angular span and depth) are dependent on the relative stress magnitudes. It is also noticed that ...
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#1H. Lin (UNSW: University of New South Wales)H-Index: 3
#2Won-Hee Kang (USYD: University of Sydney)H-Index: 16
Last. Ismet Canbulat (UNSW: University of New South Wales)H-Index: 12
view all 4 authors...
Abstract This paper presents a technique for in-situ horizontal stress prediction in vertical boreholes based on borehole breakout data using a machine learning-based meta-modelling technique, i.e. Kriging. This model is generated based on the deterministic mean function and a stationary Gaussian process function derived from the 106 data points from published experimental studies. To examine the reliability of the model, a leave-one-out cross-validation process is conducted against the publishe...
Source
#1D. Garolera (UPC: Polytechnic University of Catalonia)H-Index: 3
#2Ignacio Carol (UPC: Polytechnic University of Catalonia)H-Index: 36
Last. Panos Papanastasiou (UCY: University of Cyprus)H-Index: 24
view all 3 authors...
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Source
It is desirable to combine the stress measurement data produced by different methods to obtain a more reliable estimation of in situ stress. We present a regional case study of integrated in situ stress estimation by hydraulic fracturing, observations of borehole breakouts and drilling-induced fractures, and numerical modeling of a 1 km-deep borehole (EXP-1) in Pohang, South Korea. Prior to measuring the stress, World Stress Map (WSM) and modern field data in the Korean Peninsula are used to con...
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view all 3 authors...
A series of laboratory drilling experiments were conducted on two arkosic sandstones (Tenino and Tablerock) under polyaxial far-field stress conditions (σ h ≠ σ H ≠ σ v ). V-shaped breakouts, aligned with the σ h direction and revealing stress-dependent dimensions (width and length), were observed in the sandstones. The microscale damage pattern leading to the breakouts, however, is different between the two, which is attributed to the difference in their cementation. The dominant micromechanism...
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#1Hossein Masoumi (UNSW: University of New South Wales)H-Index: 12
#2Serkan Saydam (UNSW: University of New South Wales)H-Index: 15
Last. Paul C. Hagan (UNSW: University of New South Wales)H-Index: 18
view all 3 authors...
AbstractA suite of laboratory testing was performed on Gosford sandstone samples having a range of sizes, including point-load and uniaxial compressive tests. A unified size-effect law (USEL), based on the work by Zdenek Bazant, involving fracture energy as well as fractal theories, was introduced. It was shown that USEL correlates well with the ascending and descending uniaxial compressive strength trends obtained from Gosford sandstone as well as five other rock types reported by Brian Hawkins...
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Abstract We performed a series of borehole breakout tests on Posidonia shale to study the influence of borehole diameter on borehole stability in unconventional black shale. Thick-walled cylindrical samples (20–80 mm long, 10–50 mm in diameter) with varying borehole diameters of 1–19 mm drilled perpendicular to bedding were loaded under increasing hydrostatic pressures until formation of borehole breakouts. The critical hydrostatic pressure for breakout formation decreased significantly from abo...
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#2M. Thiercelin (UCY: University of Cyprus)H-Index: 1
In this paper the writers examine a borehole failure model that is based on fracture mechanics and layer buckling theories and compare its predictions with experimental data. The model assumes that the main failure mechanism of borehole collapse takes place in the form of (preexisting or formed) layers buckling. The model introduces a combination of fracture mechanics parameters with length dimension that scales the size of the holes, thus allowing for size effect predictions. The writers review...
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