Effect of Water Infiltration, Injection Rate and Anisotropy on Hydraulic Fracturing Behavior of Granite
Effect of Water Infiltration, Injection Rate and Anisotropy on Hydraulic Fracturing Behavior of Granite
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DOI：
10.1007/s00603-018-1431-3
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发表时间：
2019-02
影响因子：
6.2
通讯作者：
L. Zhuang;Kwang Yeom Kim;S. Jung;M. Diaz;K. Min
中科院分区：
文献类型：
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作者：
L. Zhuang;Kwang Yeom Kim;S. Jung;M. Diaz;K. Min
在1 ~ 100 mm ~ 3/s的7种不同注入速率下对抱川花岗岩圆柱体进行了水力压裂试验。并与套管压裂试验进行了对比，在套管压裂试验中，钻孔被套管化，从而排除了水渗透的影响。水的入渗对花岗岩的水力劈裂行为有显著影响，而水的入渗与花岗岩中预先存在的微裂纹以及劈理各向异性密切相关。在一定的应力条件下，花岗岩试样破裂存在一个临界注入速率。当注入速率低于临界值时，随着注入压力的缓慢增加，水渗透到花岗岩基质中，试样最终达到完全饱和，不发生破裂。在有水入渗过程中，注入压力随时间呈非线性变化，在无水入渗过程中，注入压力随时间呈近似线性变化。对于水力压裂和套管压裂试验，破裂压力随着注入速率的增加而增加。套管压裂的破裂压力比水力压裂的破裂压力高2倍以上。X射线计算机断层扫描（CT）观察表明，诱导裂缝是沿着较弱的解理平行于垂直应力的方向。在水力压裂试验中，破裂压力越高，裂缝开度越大。
Hydraulic fracturing tests on Pocheon granite cylinders at seven different injection rates varying from 1 to 100 mm3/s were conducted. They were compared with sleeve fracturing tests in which borehole was sleeved, and therefore, water infiltration influence was excluded. Hydraulic fracturing behavior of granite is significantly influenced by water infiltration, which is closely related to the preexisting microcracks in granite as well as the cleavage anisotropy. There was a threshold injection rate to fracture the granite specimen under given stress conditions. When the injection rate is below the threshold, water infiltrated granite matrix with slow increment of injection pressure, and the specimen finally reached a full saturation without fracturing. Injection pressure developed nonlinearly with time during water infiltration, while approximately linearly when infiltration was excluded. For both hydraulic and sleeve fracturing tests, breakdown pressure increases with increasing injection rate. The breakdown pressures by sleeve fracturing were more than two times higher than those in hydraulic fracturing. X-ray computed tomography (CT) observations show that induced fractures are along the weaker cleavage parallel to the direction of the vertical stress. The higher breakdown pressure results in a larger aperture of fractures in hydraulic fracturing tests.