Estimating Stress at Great Depth from Borehole Breakout

估算钻孔破裂的大深度应力

基本信息

批准号：
09044120
负责人：
HAYASHI Kazuo
金额：
$ 2.3万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09044120/
关键词：
Tectonic Stress In Situ Measurement Borehole Breakout Rock Stress Geothermal Energy HDR ブレイクアウト地圧

项目摘要

The objective of the present study is to clarify the mechanism of nucleation of borehole breakout and to examine the growth process of the borehole breakout, emphasizing the effect of the bottom of the borehole. Firstly, the characteristics of the three-dimensional elastoplastic stress field around the bottom were studied by FEM analysis, paying special attention to the singular stress field around the bottom. Then, a model of a pseudo two-dimensional stress field simulating the three-dimensional stress field was constructed, and the growth process was examined by using the pseudo stress field. The results are summarized as follows :1) Near the bottom of the borehole, stress concentration takes place at a circumferential position that is different from that at a borehole section far from the bottom. The region of stress concentration is very localized.2) Thus, for a rock that is insensitive to a local stress field in fracture nucleation, borehole break out is not formed at the bottom of borehole.3) Variation of the stress field with respect to the distance between the bottom and the observation position, can be seen as the time variation of stress at a fixed depth during drilling. The geometry of borehole breakout calculated by following exactly the loading path just mentioned is almost the same as that estimated by two-dimensional approach.4) Therefore, the breakout can be considered to be formed on the wall of a cylindrical cavity in an elastoplastic medium subjected to a monotonically increasing load at infinity.5) The width of the breakout is almost the same as that estimated by purely elastic stress state, indicating the validity of the hypothesis proposed by Haimson et al. on the relationship between the width and the far field stress.

本研究的目的是阐明钻孔破裂的成核机制并检查钻孔破裂的生长过程，强调钻孔底部的影响。首先，通过有限元分析研究了底部周围三维弹塑性应力场的特征，特别关注底部周围的奇异应力场。然后，构建了模拟三维应力场的伪二维应力场模型，并利用伪应力场研究了生长过程。研究结果如下：1)在靠近井底的位置，应力集中的周向位置与远离井底的井段不同。应力集中区域非常局部化。2) 因此，对于裂缝成核时对局部应力场不敏感的岩石，钻孔底部不会形成井眼破裂。3) 应力场相对于底部到观测位置的距离，可以看作是钻井过程中固定深度处应力随时间的变化。精确遵循刚刚提到的加载路径计算出的钻孔破裂几何形状与二维方法估计的几乎相同。 4）因此，破裂可以被认为是在弹塑性介质中的圆柱形空腔壁上形成的5）突破宽度与纯弹性应力状态估计的宽度几乎相同，表明Haimson等人提出的假设的有效性。宽度与远场应力之间的关系。