Estimation of horizontal stress magnitudes from borehole breakouts has been an attractive topic in the petroleum and mining industries, although there are critical research gaps that remain unfilled. In this paper, numerical simulation is conducted on Gosford sandstone to investigate the borehole breakout and its associated borehole size effect, including temperature influence. The discrete element method (DEM) model shows that the borehole breakout angular span is constant after the initial formation, whereas its depth propagates along the minimum horizontal stress direction. This indicates that the breakout angular span is a reliable parameter for horizontal stress estimation. The borehole size effect simulations illustrated the importance of borehole size on breakout geometries in which smaller borehole size leads to higher breakout initiation stress as well as the stress re-distribution from borehole wall outwards through micro-cracking. This implies that the stress may be averaged over a distance around the borehole and breakout initiation occurs at the borehole wall rather than some distance into the rock. In addition, the numerical simulation incorporated the thermal effect which is widely encountered in deep geothermal wells. Based on the results, the higher temperature led to lower breakout initiation stress with same borehole size, and more proportion of shear cracks was generated under higher temperature. This indicates that the temperature might contribute to the micro-fracturing mode and hence influences the horizontal stress estimation results from borehole breakout geometries. Numerical simulation showed that breakout shape and dimensions changed considerably under high stress and high temperature conditions, suggesting that the temperature may need to be considered for breakout stress analysis in deep locations.

尽管仍然存在一些关键的研究空白，但从井眼破裂中估计水平应力大小一直是石油和采矿行业的一个有吸引力的话题。在本文中，对Gosford砂岩进行了数值模拟，以研究井眼破裂及其相关的井眼尺寸效应，包括温度影响。离散元法（DEM）模型表明，井眼破裂角跨度在初始形成后是恒定的，而其深度沿最小水平应力方向传播。这表明突围角跨度是用于水平应力估算的可靠参数。井眼尺寸效应模拟说明了井眼尺寸对井眼几何形状的重要性，其中较小的井眼尺寸会导致较高的井眼初始应力以及应力通过井眼微裂缝从井眼壁向外重新分布。这意味着应力可以在整个井眼周围的某个距离上平均，并且在井壁处而不是到岩石中的某个距离处会发生破裂。另外，数值模拟结合了深地热井中广泛遇到的热效应。根据结果​​，在相同的井眼尺寸下，较高的温度导致较低的破裂初始应力，并且在较高的温度下产生更大比例的剪切裂纹。这表明温度可能有助于微裂缝模式，因此会影响井眼破裂几何形状的水平应力估算结果。数值模拟表明，在高应力和高温条件下，突围的形状和尺寸发生了很大变化，这表明在深处进行突围应力分析时可能需要考虑温度。