Experimental and Analytical Investigations of the Effect of Hole Size on Borehole Breakout Geometries for Estimation of In Situ Stresses
Experimental and Analytical Investigations of the Effect of Hole Size on Borehole Breakout Geometries for Estimation of In Situ Stresses
复制标题
孔径尺寸对钻孔破裂几何形状影响的实验和分析研究，用于估计地应力
DOI：
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发表时间：
2019
影响因子：
6.2
通讯作者：
T. R. Stacey
中科院分区：
文献类型：
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作者：
H. Lin;J. Oh;I. Canbulat;T. R. Stacey
钻孔崩落是岩石钻孔中由于诱发应力集中而产生的一种自然现象。许多研究人员试图将这种现象与原地应力大小联系起来。本文对不同孔径预钻孔砂岩块体（120 × 120 × 120 mm 3）进行了真三轴试验。结果证实，断裂几何形状（角度跨度和深度）取决于相对应力大小。还注意到，较大的孔尺寸（孔半径）产生较宽的角跨度和较深的归一化深度（崩落深度/孔尺寸），这表明孔尺寸是崩落几何形状的重要参数。此外，对以往实验研究的分析表明，两种崩落几何形状之间的关系不是唯一的，并且受水平应力大小的影响很大。对现有模型的分析还表明，在一定的应力强度条件下，角跨度可以随着水平应力比的增大而变窄。这两种分析表明，崩落的几何形状不仅相互依赖，而且还取决于水平应力大小。这导致了一个初步的结论，崩落几何形状可能不是多余的因素，并可能用于水平应力估计。
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 mm 3 ) 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 a larger hole size (hole radius) yielded a wider angular span and deeper normalised depth (breakout depth/hole size), which indicates that hole size is an important parameter for breakout geometries. In addition, the analysis on previous experimental studies suggested that the relationship between two breakout geometries is not unique and is heavily influenced by the horizontal stress magnitudes. The analysis of the existing model also revealed the angular span may be narrowed with increasing horizontal stress ratio under a certain stress–strength condition. Both analyses indicate the breakout geometries are not only dependent on each other but also on the horizontal stress magnitudes. This leads to a tentative conclusion that breakout geometries may not be redundant factors and might be used for horizontal stress estimation.